ssl --- 套接字对象的 TLS/SSL 包装器

源代码: Lib/ssl.py

---

本模块保证了对传安全传输层协议（TLS）的访问 (SSL)加密，并且提供客户端和服务端层面的网络嵌套字层面的对等连接认证技术。本模块使用OpenSSL库。适用于所有现代Unix系统、Windows以及Mac OS X。只要Open SSL存在的系统，都有机会正常使用。

注解

某些行为可能具有平台依赖，因为调用是根据操作系统的嵌套字API。不同版本的Open SSL也会引起差异：例如Open SSL版本1.0.1 自带TLSv1.1 和 TLSv1.2

警告

在阅读 Security considerations 前不要使用此模块。 这样做可能会导致虚假的安全感，因为ssl模块的默认设置不一定适合你的应用程序。

本文档记录"ssl"模块的对象和函数；更多关于TLS,SSL,和证书的信息，请参阅下方的“详情”选项

本模块提供了一个类 ssl.SSLSocket，它派生自 socket.socket 类型，并提供类似套接字的包装器，也能够对通过带 SSL 套接字的数据进行加密和解密。 它支持一些额外方法例如 getpeercert()，该方法可从连接的另一端获取证书，还有 cipher()，该方法可获取安全连接所使用的密码。

对于更复杂的应用程序，ssl.SSLContext 类有助于管理设置项和证书，进而可以被使用 SSLContext.wrap_socket() 方法创建的 SSL 套接字继承。

在 3.5.3 版更改: 更新以支持和 OpenSSL 1.1.0 的链接

在 3.6 版更改: OpenSSL 0.9.8、1.0.0 和 1.0.1 已过时，将不再被支持。在 ssl 模块未来的版本中，最低需要 OpenSSL 1.0.2 或 1.1.0。

方法、常量和异常处理

套接字创建

从 Python 3.2 和 2.7.9 开始，建议使用 SSLContext 实例的 SSLContext.wrap_socket() 来将套接字包装为 SSLSocket 对象。 辅助函数 create_default_context() 会返回一个新的带有安全默认设置的上下文。 旧的 wrap_socket() 函数已被弃用，因为它效率较差并且不支持服务器名称提示（SNI）和主机匹配。

客户端套接字实例，采用默认上下文和IPv4/IPv6双栈:

import socket
import ssl

hostname = 'www.python.org'
context = ssl.create_default_context()

with socket.create_connection((hostname, 443)) as sock:
    with context.wrap_socket(sock, server_hostname=hostname) as ssock:
        print(ssock.version())

客户端套接字示例，带有自定义上下文和IPv4:

hostname = 'www.python.org'
# PROTOCOL_TLS_CLIENT requires valid cert chain and hostname
context = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
context.load_verify_locations('path/to/cabundle.pem')

with socket.socket(socket.AF_INET, socket.SOCK_STREAM, 0) as sock:
    with context.wrap_socket(sock, server_hostname=hostname) as ssock:
        print(ssock.version())

服务器套接字实例，在localhost上监听IPv4:

context = ssl.SSLContext(ssl.PROTOCOL_TLS_SERVER)
context.load_cert_chain('/path/to/certchain.pem', '/path/to/private.key')

with socket.socket(socket.AF_INET, socket.SOCK_STREAM, 0) as sock:
    sock.bind(('127.0.0.1', 8443))
    sock.listen(5)
    with context.wrap_socket(sock, server_side=True) as ssock:
        conn, addr = ssock.accept()
        ...

上下文创建

便捷函数，可以帮助创建 SSLContext 对象，用于常见的目的。

ssl.create_default_context(purpose=Purpose.SERVER_AUTH, cafile=None, capath=None, cadata=None)

返回一个新的 SSLContext 对象，使用给定 purpose 的默认设置。 该设置由 ssl 模块选择，并且通常是代表一个比直接调用 SSLContext 构造器时更高的安全等级。

cafile, capath, cadata 代表用于进行证书核验的可选受信任 CA 证书，与 SSLContext.load_verify_locations() 的一致。 如果三个参数均为 None，此函数可以转而选择信任系统的默认 CA 证书。

设置包括: PROTOCOL_TLS, OP_NO_SSLv2 以及 OP_NO_SSLv3，具有不带 RC4 和不带无身份验证密码套件的高度加密密码套件。 传入 SERVER_AUTH 作为 purpose 会把 verify_mode 设为 CERT_REQUIRED 并且加载指定 CA 证书（当给出 cafile, capath 和 cadata 中的至少一个）或者使用 SSLContext.load_default_certs() 来加载默认 CA 证书。

当 keylog_filename 受支持并且设置了环境变量 SSLKEYLOGFILE 时，create_default_context() 会启用密钥日志记录。

注解

协议、选项、密码和其他设置可随时更改为更具约束性的值而无须事先弃用。 这些值代表了兼容性和安全性之间的合理平衡。

如果你的应用需要特定的设置，你应当创建一个 SSLContext 并自行应用设置。

注解

如果你发现当某些较旧的客户端或服务器尝试与用此函数创建的 SSLContext 进行连接时收到了报错提示 "Protocol or cipher suite mismatch"，这可能是因为它们只支持 SSL3.0 而它被此函数用 OP_NO_SSLv3 排除掉了。 SSL3.0 被广泛认为 完全不可用。 如果你仍希望继续使用此函数但仍允许 SSL 3.0 连接，你可以使用以下代码重新启用它们:

ctx = ssl.create_default_context(Purpose.CLIENT_AUTH)
ctx.options &= ~ssl.OP_NO_SSLv3

3.4 新版功能.

在 3.4.4 版更改: RC4 被从默认密码字符串中丢弃。

在 3.6 版更改: ChaCha20/Poly1305 被添加到默认密码字符串中。

3DES 被从默认密码字符串中丢弃。

在 3.8 版更改: 增加了对密钥日志记录至 SSLKEYLOGFILE 的支持。

异常

exception ssl.SSLError

引发此异常以提示来自下层 SSL 实现（目前由 OpenSSL 库提供）的错误。 它表示在下层网络连接之上叠加的高层级加密和验证层存在某种问题。 此错误是 OSError 的一个子类型。 SSLError 实例的错误和消息是由 OpenSSL 库提供的。

在 3.3 版更改: SSLError 曾经是 socket.error 的一个子类型。

library

一个字符串形式的助记符，用来指明发生错误的 OpenSSL 子模块，例如 SSL, PEM 或 X509。 可能的取值范围依赖于 OpenSSL 的版本。

3.3 新版功能.

reason

一个字符串形式的助记符，用来指明发生错误的原因，例如 CERTIFICATE_VERIFY_FAILED。 可能的取值范围依赖于 OpenSSL 的版本。

3.3 新版功能.

exception ssl.SSLZeroReturnError

SSLError 的子类，当尝试读取或写入且 SSL 连接已被完全关闭时会被引发。 请注意这并不意味着下层的传输（读取 TCP）已被关闭。

3.3 新版功能.

exception ssl.SSLWantReadError

SSLError 的子类，当尝试读取或写入数据，但在请求被满足之前还需要在下层的 TCP 传输上接收更多数据时会被 非阻塞型 SSL 套接字 引发。

3.3 新版功能.

exception ssl.SSLWantWriteError

SSLError 的子类，当尝试读取或写入数据，但在请求被满足之前还需要在下层的 TCP 传输上发送更多数据时会被 非阻塞型 SSL 套接字 引发。

3.3 新版功能.

exception ssl.SSLSyscallError

SSLError 的子类，当尝试在 SSL 套接字上执行操作时遇到系统错误时会被引发。 不幸的是，没有简单的方式能检查原始 errno 编号。

3.3 新版功能.

exception ssl.SSLEOFError

SSLError 的子类，当 SSL 连接被突然终止时会被引发。 通常，当遇到此错误时你不应再尝试重用下层的传输。

3.3 新版功能.

exception ssl.SSLCertVerificationError

SSLError 的子类，当证书验证失败时会被引发。

3.7 新版功能.

verify_code

一个数字形式的错误编号，用于表示验证错误。

verify_message

用于表示验证错误的人类可读的字符串。

exception ssl.CertificateError

SSLCertVerificationError 的别名。

在 3.7 版更改: 此异常现在是 SSLCertVerificationError 的别名。

随机生成

ssl.RAND_bytes(num)

返回 num 个高加密强度伪随机字节数据。 如果 PRNG 未使用足够的数据作为随机种子或者如果当前 RAND 方法不支持该操作则会引发 SSLError。 RAND_status() 可被用来检查 PRNG 的状态而 RAND_add() 可被用来为 PRNG 设置随机种子。

对于几乎所有应用程序都更推荐使用 os.urandom()。

请阅读维基百科文章 Cryptographically secure pseudorandom number generator (CSPRNG) 以了解对于高加密强度生成器的具体要求。

3.3 新版功能.

ssl.RAND_pseudo_bytes(num)

返回 (bytes, is_cryptographic): bytes 是 num 个伪随机字节数据，如果所生成的字节数据为高加密强度则 is_cryptographic 为 True。 如果当前 RAND 方法不支持此操作则会引发 SSLError。

所生成的伪随机字节序列如果具有足够的长度则将会具有唯一性，并是并非不可预测。 它们可被用于非加密目的以及加密协议中的特定目的，但通常不可被用于密钥生成等目的。

对于几乎所有应用程序都更推荐使用 os.urandom()。

3.3 新版功能.

3.6 版后已移除: OpenSSL 已弃用了 ssl.RAND_pseudo_bytes()，请改用 ssl.RAND_bytes()。

ssl.RAND_status()

如果 SSL 伪随机数生成器已使用‘足够的’随机性作为种子则返回 True，否则返回 False。 你可以使用 ssl.RAND_egd() 和 ssl.RAND_add() 来增加伪随机数生成器的随机性。

ssl.RAND_egd(path)

如果你在某处运行了一个熵收集守护程序（EGD），且 path 是向其打开的套接字连接路径名，此函数将从该套接字读取 256 个字节的随机性数据，并将其添加到 SSL 伪随机数生成器以增加所生成密钥的安全性。 此操作通常只在没有更好随机性源的系统上才是必要的。

请查看 http://egd.sourceforge.net/ 或 http://prngd.sourceforge.net/ 来了解有关熵收集守护程序源的信息。

可用性: 对于 LibreSSL 和 OpenSSL > 1.1.0 不可用。

ssl.RAND_add(bytes, entropy)

将给定的 bytes 混合到 SSL 伪随机数生成器中。 形参 entropy (float 类型) 是数据所包含的熵的下界 (因此你可以总是使用 0.0)。 请查看 RFC 1750 了解有关熵源的更多信息。

在 3.5 版更改: 现在接受可写的 字节类对象。

证书处理

ssl.match_hostname(cert, hostname)

验证 cert (使用 SSLSocket.getpeercert() 所返回的已解码格式) 是否匹配给定的 hostname。 所应用的规则是在 RFC 2818, RFC 5280 和 RFC 6125 中描述的检查 HTTPS 服务器身份的规则。 除了 HTTPS，此函数还应当适用于各种基于 SSL 协议的服务器身份检查操作，例如 FTPS, IMAPS, POPS 等等。

失败时引发 CertificateError。 成功时此函数无返回值:

>>> cert = {'subject': ((('commonName', 'example.com'),),)}
>>> ssl.match_hostname(cert, "example.com")
>>> ssl.match_hostname(cert, "example.org")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/py3k/Lib/ssl.py", line 130, in match_hostname
ssl.CertificateError: hostname 'example.org' doesn't match 'example.com'

3.2 新版功能.

在 3.3.3 版更改: 此函数现在遵循 RFC 6125, 6.4.3 小节，它不会匹配多个通配符 (例如 *.*.com 或 *a*.example.org) 也不匹配国际化域名 (IDN) 片段内部的通配符。 IDN A 标签例如 www*.xn--pthon-kva.org 仍然受支持，但 x*.python.org 不再能匹配 xn--tda.python.org。

在 3.5 版更改: 现在支持匹配存在于证书的 subjectAltName 字段中的 IP 地址。

在 3.7 版更改: 此函数不再被用于 TLS 连接。 主机匹配现在是由 OpenSSL 执行的。

允许位于段的最左端且为唯一字符的通配符。 部分通配符例如 www*.example.com 已不再受支持。

3.7 版后已移除.

ssl.cert_time_to_seconds(cert_time)

Return the time in seconds since the Epoch, given the cert_time string representing the "notBefore" or "notAfter" date from a certificate in "%b %d %H:%M:%S %Y %Z" strptime format (C locale).

Here's an example:

>>> import ssl
>>> timestamp = ssl.cert_time_to_seconds("Jan  5 09:34:43 2018 GMT")
>>> timestamp  
1515144883
>>> from datetime import datetime
>>> print(datetime.utcfromtimestamp(timestamp))  
2018-01-05 09:34:43

"notBefore" or "notAfter" dates must use GMT (RFC 5280).

在 3.5 版更改: Interpret the input time as a time in UTC as specified by 'GMT' timezone in the input string. Local timezone was used previously. Return an integer (no fractions of a second in the input format)

ssl.get_server_certificate(addr, ssl_version=PROTOCOL_TLS, ca_certs=None)

Given the address addr of an SSL-protected server, as a (hostname, port-number) pair, fetches the server's certificate, and returns it as a PEM-encoded string. If ssl_version is specified, uses that version of the SSL protocol to attempt to connect to the server. If ca_certs is specified, it should be a file containing a list of root certificates, the same format as used for the same parameter in SSLContext.wrap_socket(). The call will attempt to validate the server certificate against that set of root certificates, and will fail if the validation attempt fails.

在 3.3 版更改: This function is now IPv6-compatible.

在 3.5 版更改: The default ssl_version is changed from PROTOCOL_SSLv3 to PROTOCOL_TLS for maximum compatibility with modern servers.

ssl.DER_cert_to_PEM_cert(DER_cert_bytes)

Given a certificate as a DER-encoded blob of bytes, returns a PEM-encoded string version of the same certificate.

ssl.PEM_cert_to_DER_cert(PEM_cert_string)

Given a certificate as an ASCII PEM string, returns a DER-encoded sequence of bytes for that same certificate.

ssl.get_default_verify_paths()

Returns a named tuple with paths to OpenSSL's default cafile and capath. The paths are the same as used by SSLContext.set_default_verify_paths(). The return value is a named tuple DefaultVerifyPaths:

• cafile - resolved path to cafile or None if the file doesn't exist,

• capath - resolved path to capath or None if the directory doesn't exist,

• openssl_cafile_env - OpenSSL's environment key that points to a cafile,

• openssl_cafile - hard coded path to a cafile,

• openssl_capath_env - OpenSSL's environment key that points to a capath,

• openssl_capath - hard coded path to a capath directory

Availability: LibreSSL ignores the environment vars openssl_cafile_env and openssl_capath_env.

3.4 新版功能.

ssl.enum_certificates(store_name)

Retrieve certificates from Windows' system cert store. store_name may be one of CA, ROOT or MY. Windows may provide additional cert stores, too.

The function returns a list of (cert_bytes, encoding_type, trust) tuples. The encoding_type specifies the encoding of cert_bytes. It is either x509_asn for X.509 ASN.1 data or pkcs_7_asn for PKCS#7 ASN.1 data. Trust specifies the purpose of the certificate as a set of OIDS or exactly True if the certificate is trustworthy for all purposes.

示例:

>>> ssl.enum_certificates("CA")
[(b'data...', 'x509_asn', {'1.3.6.1.5.5.7.3.1', '1.3.6.1.5.5.7.3.2'}),
 (b'data...', 'x509_asn', True)]

可用性: Windows。

3.4 新版功能.

ssl.enum_crls(store_name)

Retrieve CRLs from Windows' system cert store. store_name may be one of CA, ROOT or MY. Windows may provide additional cert stores, too.

The function returns a list of (cert_bytes, encoding_type, trust) tuples. The encoding_type specifies the encoding of cert_bytes. It is either x509_asn for X.509 ASN.1 data or pkcs_7_asn for PKCS#7 ASN.1 data.

可用性: Windows。

3.4 新版功能.

ssl.wrap_socket(sock, keyfile=None, certfile=None, server_side=False, cert_reqs=CERT_NONE, ssl_version=PROTOCOL_TLS, ca_certs=None, do_handshake_on_connect=True, suppress_ragged_eofs=True, ciphers=None)

Takes an instance sock of socket.socket, and returns an instance of ssl.SSLSocket, a subtype of socket.socket, which wraps the underlying socket in an SSL context. sock must be a SOCK_STREAM socket; other socket types are unsupported.

Internally, function creates a SSLContext with protocol ssl_version and SSLContext.options set to cert_reqs. If parameters keyfile, certfile, ca_certs or ciphers are set, then the values are passed to SSLContext.load_cert_chain(), SSLContext.load_verify_locations(), and SSLContext.set_ciphers().

The arguments server_side, do_handshake_on_connect, and suppress_ragged_eofs have the same meaning as SSLContext.wrap_socket().

3.7 版后已移除: Since Python 3.2 and 2.7.9, it is recommended to use the SSLContext.wrap_socket() instead of wrap_socket(). The top-level function is limited and creates an insecure client socket without server name indication or hostname matching.

常数

All constants are now enum.IntEnum or enum.IntFlag collections.

3.6 新版功能.

ssl.CERT_NONE

Possible value for SSLContext.verify_mode, or the cert_reqs parameter to wrap_socket(). Except for PROTOCOL_TLS_CLIENT, it is the default mode. With client-side sockets, just about any cert is accepted. Validation errors, such as untrusted or expired cert, are ignored and do not abort the TLS/SSL handshake.

In server mode, no certificate is requested from the client, so the client does not send any for client cert authentication.

See the discussion of Security considerations below.

ssl.CERT_OPTIONAL

Possible value for SSLContext.verify_mode, or the cert_reqs parameter to wrap_socket(). In client mode, CERT_OPTIONAL has the same meaning as CERT_REQUIRED. It is recommended to use CERT_REQUIRED for client-side sockets instead.

In server mode, a client certificate request is sent to the client. The client may either ignore the request or send a certificate in order perform TLS client cert authentication. If the client chooses to send a certificate, it is verified. Any verification error immediately aborts the TLS handshake.

Use of this setting requires a valid set of CA certificates to be passed, either to SSLContext.load_verify_locations() or as a value of the ca_certs parameter to wrap_socket().

ssl.CERT_REQUIRED

Possible value for SSLContext.verify_mode, or the cert_reqs parameter to wrap_socket(). In this mode, certificates are required from the other side of the socket connection; an SSLError will be raised if no certificate is provided, or if its validation fails. This mode is not sufficient to verify a certificate in client mode as it does not match hostnames. check_hostname must be enabled as well to verify the authenticity of a cert. PROTOCOL_TLS_CLIENT uses CERT_REQUIRED and enables check_hostname by default.

With server socket, this mode provides mandatory TLS client cert authentication. A client certificate request is sent to the client and the client must provide a valid and trusted certificate.

Use of this setting requires a valid set of CA certificates to be passed, either to SSLContext.load_verify_locations() or as a value of the ca_certs parameter to wrap_socket().

class ssl.VerifyMode

enum.IntEnum collection of CERT_* constants.

3.6 新版功能.

ssl.VERIFY_DEFAULT

Possible value for SSLContext.verify_flags. In this mode, certificate revocation lists (CRLs) are not checked. By default OpenSSL does neither require nor verify CRLs.

3.4 新版功能.

ssl.VERIFY_CRL_CHECK_LEAF

Possible value for SSLContext.verify_flags. In this mode, only the peer cert is checked but none of the intermediate CA certificates. The mode requires a valid CRL that is signed by the peer cert's issuer (its direct ancestor CA). If no proper CRL has been loaded with SSLContext.load_verify_locations, validation will fail.

3.4 新版功能.

ssl.VERIFY_CRL_CHECK_CHAIN

Possible value for SSLContext.verify_flags. In this mode, CRLs of all certificates in the peer cert chain are checked.

3.4 新版功能.

ssl.VERIFY_X509_STRICT

Possible value for SSLContext.verify_flags to disable workarounds for broken X.509 certificates.

3.4 新版功能.

ssl.VERIFY_X509_TRUSTED_FIRST

Possible value for SSLContext.verify_flags. It instructs OpenSSL to prefer trusted certificates when building the trust chain to validate a certificate. This flag is enabled by default.

3.4.4 新版功能.

class ssl.VerifyFlags

enum.IntFlag collection of VERIFY_* constants.

3.6 新版功能.

ssl.PROTOCOL_TLS

Selects the highest protocol version that both the client and server support. Despite the name, this option can select both "SSL" and "TLS" protocols.

3.6 新版功能.

ssl.PROTOCOL_TLS_CLIENT

Auto-negotiate the highest protocol version like PROTOCOL_TLS, but only support client-side SSLSocket connections. The protocol enables CERT_REQUIRED and check_hostname by default.

3.6 新版功能.

ssl.PROTOCOL_TLS_SERVER

Auto-negotiate the highest protocol version like PROTOCOL_TLS, but only support server-side SSLSocket connections.

3.6 新版功能.

ssl.PROTOCOL_SSLv23

Alias for PROTOCOL_TLS.

3.6 版后已移除: Use PROTOCOL_TLS instead.

ssl.PROTOCOL_SSLv2

Selects SSL version 2 as the channel encryption protocol.

This protocol is not available if OpenSSL is compiled with the OPENSSL_NO_SSL2 flag.

警告

SSL version 2 is insecure. Its use is highly discouraged.

3.6 版后已移除: OpenSSL has removed support for SSLv2.

ssl.PROTOCOL_SSLv3

Selects SSL version 3 as the channel encryption protocol.

This protocol is not be available if OpenSSL is compiled with the OPENSSL_NO_SSLv3 flag.

警告

SSL version 3 is insecure. Its use is highly discouraged.

3.6 版后已移除: OpenSSL has deprecated all version specific protocols. Use the default protocol PROTOCOL_TLS with flags like OP_NO_SSLv3 instead.

ssl.PROTOCOL_TLSv1

Selects TLS version 1.0 as the channel encryption protocol.

3.6 版后已移除: OpenSSL has deprecated all version specific protocols. Use the default protocol PROTOCOL_TLS with flags like OP_NO_SSLv3 instead.

ssl.PROTOCOL_TLSv1_1

Selects TLS version 1.1 as the channel encryption protocol. Available only with openssl version 1.0.1+.

3.4 新版功能.

3.6 版后已移除: OpenSSL has deprecated all version specific protocols. Use the default protocol PROTOCOL_TLS with flags like OP_NO_SSLv3 instead.

ssl.PROTOCOL_TLSv1_2

Selects TLS version 1.2 as the channel encryption protocol. This is the most modern version, and probably the best choice for maximum protection, if both sides can speak it. Available only with openssl version 1.0.1+.

3.4 新版功能.

3.6 版后已移除: OpenSSL has deprecated all version specific protocols. Use the default protocol PROTOCOL_TLS with flags like OP_NO_SSLv3 instead.

ssl.OP_ALL

Enables workarounds for various bugs present in other SSL implementations. This option is set by default. It does not necessarily set the same flags as OpenSSL's SSL_OP_ALL constant.

3.2 新版功能.

ssl.OP_NO_SSLv2

Prevents an SSLv2 connection. This option is only applicable in conjunction with PROTOCOL_TLS. It prevents the peers from choosing SSLv2 as the protocol version.

3.2 新版功能.

3.6 版后已移除: SSLv2 is deprecated

ssl.OP_NO_SSLv3

Prevents an SSLv3 connection. This option is only applicable in conjunction with PROTOCOL_TLS. It prevents the peers from choosing SSLv3 as the protocol version.

3.2 新版功能.

3.6 版后已移除: SSLv3 is deprecated

ssl.OP_NO_TLSv1

Prevents a TLSv1 connection. This option is only applicable in conjunction with PROTOCOL_TLS. It prevents the peers from choosing TLSv1 as the protocol version.

3.2 新版功能.

3.7 版后已移除: The option is deprecated since OpenSSL 1.1.0, use the new SSLContext.minimum_version and SSLContext.maximum_version instead.

ssl.OP_NO_TLSv1_1

Prevents a TLSv1.1 connection. This option is only applicable in conjunction with PROTOCOL_TLS. It prevents the peers from choosing TLSv1.1 as the protocol version. Available only with openssl version 1.0.1+.

3.4 新版功能.

3.7 版后已移除: The option is deprecated since OpenSSL 1.1.0.

ssl.OP_NO_TLSv1_2

Prevents a TLSv1.2 connection. This option is only applicable in conjunction with PROTOCOL_TLS. It prevents the peers from choosing TLSv1.2 as the protocol version. Available only with openssl version 1.0.1+.

3.4 新版功能.

3.7 版后已移除: The option is deprecated since OpenSSL 1.1.0.

ssl.OP_NO_TLSv1_3

Prevents a TLSv1.3 connection. This option is only applicable in conjunction with PROTOCOL_TLS. It prevents the peers from choosing TLSv1.3 as the protocol version. TLS 1.3 is available with OpenSSL 1.1.1 or later. When Python has been compiled against an older version of OpenSSL, the flag defaults to 0.

3.7 新版功能.

3.7 版后已移除: The option is deprecated since OpenSSL 1.1.0. It was added to 2.7.15, 3.6.3 and 3.7.0 for backwards compatibility with OpenSSL 1.0.2.

ssl.OP_NO_RENEGOTIATION

Disable all renegotiation in TLSv1.2 and earlier. Do not send HelloRequest messages, and ignore renegotiation requests via ClientHello.

This option is only available with OpenSSL 1.1.0h and later.

3.7 新版功能.

ssl.OP_CIPHER_SERVER_PREFERENCE

Use the server's cipher ordering preference, rather than the client's. This option has no effect on client sockets and SSLv2 server sockets.

3.3 新版功能.

ssl.OP_SINGLE_DH_USE

Prevents re-use of the same DH key for distinct SSL sessions. This improves forward secrecy but requires more computational resources. This option only applies to server sockets.

3.3 新版功能.

ssl.OP_SINGLE_ECDH_USE

Prevents re-use of the same ECDH key for distinct SSL sessions. This improves forward secrecy but requires more computational resources. This option only applies to server sockets.

3.3 新版功能.

ssl.OP_ENABLE_MIDDLEBOX_COMPAT

Send dummy Change Cipher Spec (CCS) messages in TLS 1.3 handshake to make a TLS 1.3 connection look more like a TLS 1.2 connection.

This option is only available with OpenSSL 1.1.1 and later.

3.8 新版功能.

ssl.OP_NO_COMPRESSION

Disable compression on the SSL channel. This is useful if the application protocol supports its own compression scheme.

This option is only available with OpenSSL 1.0.0 and later.

3.3 新版功能.

class ssl.Options

enum.IntFlag collection of OP_* constants.

ssl.OP_NO_TICKET

Prevent client side from requesting a session ticket.

3.6 新版功能.

ssl.HAS_ALPN

Whether the OpenSSL library has built-in support for the Application-Layer Protocol Negotiation TLS extension as described in RFC 7301.

3.5 新版功能.

ssl.HAS_NEVER_CHECK_COMMON_NAME

Whether the OpenSSL library has built-in support not checking subject common name and SSLContext.hostname_checks_common_name is writeable.

3.7 新版功能.

ssl.HAS_ECDH

Whether the OpenSSL library has built-in support for the Elliptic Curve-based Diffie-Hellman key exchange. This should be true unless the feature was explicitly disabled by the distributor.

3.3 新版功能.

ssl.HAS_SNI

Whether the OpenSSL library has built-in support for the Server Name Indication extension (as defined in RFC 6066).

3.2 新版功能.

ssl.HAS_NPN

Whether the OpenSSL library has built-in support for the Next Protocol Negotiation as described in the Application Layer Protocol Negotiation. When true, you can use the SSLContext.set_npn_protocols() method to advertise which protocols you want to support.

3.3 新版功能.

ssl.HAS_SSLv2

Whether the OpenSSL library has built-in support for the SSL 2.0 protocol.

3.7 新版功能.

ssl.HAS_SSLv3

Whether the OpenSSL library has built-in support for the SSL 3.0 protocol.

3.7 新版功能.

ssl.HAS_TLSv1

Whether the OpenSSL library has built-in support for the TLS 1.0 protocol.

3.7 新版功能.

ssl.HAS_TLSv1_1

Whether the OpenSSL library has built-in support for the TLS 1.1 protocol.

3.7 新版功能.

ssl.HAS_TLSv1_2

Whether the OpenSSL library has built-in support for the TLS 1.2 protocol.

3.7 新版功能.

ssl.HAS_TLSv1_3

Whether the OpenSSL library has built-in support for the TLS 1.3 protocol.

3.7 新版功能.

ssl.CHANNEL_BINDING_TYPES

List of supported TLS channel binding types. Strings in this list can be used as arguments to SSLSocket.get_channel_binding().

3.3 新版功能.

ssl.OPENSSL_VERSION

The version string of the OpenSSL library loaded by the interpreter:

>>> ssl.OPENSSL_VERSION
'OpenSSL 1.0.2k  26 Jan 2017'

3.2 新版功能.

ssl.OPENSSL_VERSION_INFO

A tuple of five integers representing version information about the OpenSSL library:

>>> ssl.OPENSSL_VERSION_INFO
(1, 0, 2, 11, 15)

3.2 新版功能.

ssl.OPENSSL_VERSION_NUMBER

The raw version number of the OpenSSL library, as a single integer:

>>> ssl.OPENSSL_VERSION_NUMBER
268443839
>>> hex(ssl.OPENSSL_VERSION_NUMBER)
'0x100020bf'

3.2 新版功能.

ssl.ALERT_DESCRIPTION_HANDSHAKE_FAILURE

ssl.ALERT_DESCRIPTION_INTERNAL_ERROR

ALERT_DESCRIPTION_*

Alert Descriptions from RFC 5246 and others. The IANA TLS Alert Registry contains this list and references to the RFCs where their meaning is defined.

Used as the return value of the callback function in SSLContext.set_servername_callback().

3.4 新版功能.

class ssl.AlertDescription

enum.IntEnum collection of ALERT_DESCRIPTION_* constants.

3.6 新版功能.

Purpose.SERVER_AUTH

Option for create_default_context() and SSLContext.load_default_certs(). This value indicates that the context may be used to authenticate Web servers (therefore, it will be used to create client-side sockets).

3.4 新版功能.

Purpose.CLIENT_AUTH

Option for create_default_context() and SSLContext.load_default_certs(). This value indicates that the context may be used to authenticate Web clients (therefore, it will be used to create server-side sockets).

3.4 新版功能.

class ssl.SSLErrorNumber

enum.IntEnum collection of SSL_ERROR_* constants.

3.6 新版功能.

class ssl.TLSVersion

enum.IntEnum collection of SSL and TLS versions for SSLContext.maximum_version and SSLContext.minimum_version.

3.7 新版功能.

TLSVersion.MINIMUM_SUPPORTED

TLSVersion.MAXIMUM_SUPPORTED

The minimum or maximum supported SSL or TLS version. These are magic constants. Their values don't reflect the lowest and highest available TLS/SSL versions.

TLSVersion.SSLv3

TLSVersion.TLSv1

TLSVersion.TLSv1_1

TLSVersion.TLSv1_2

TLSVersion.TLSv1_3

SSL 3.0 to TLS 1.3.

SSL Sockets

class ssl.SSLSocket(socket.socket)

SSL sockets provide the following methods of 套接字对象:

• accept()

• bind()

• close()

• connect()

• detach()

• fileno()

• getpeername(), getsockname()

• getsockopt(), setsockopt()

• gettimeout(), settimeout(), setblocking()

• listen()

• makefile()

• recv(), recv_into() (but passing a non-zero flags argument is not allowed)

• send(), sendall() (with the same limitation)

• sendfile() (but os.sendfile will be used for plain-text sockets only, else send() will be used)

• shutdown()

However, since the SSL (and TLS) protocol has its own framing atop of TCP, the SSL sockets abstraction can, in certain respects, diverge from the specification of normal, OS-level sockets. See especially the notes on non-blocking sockets.

Instances of SSLSocket must be created using the SSLContext.wrap_socket() method.

在 3.5 版更改: The sendfile() method was added.

在 3.5 版更改: The shutdown() does not reset the socket timeout each time bytes are received or sent. The socket timeout is now to maximum total duration of the shutdown.

3.6 版后已移除: It is deprecated to create a SSLSocket instance directly, use SSLContext.wrap_socket() to wrap a socket.

在 3.7 版更改: SSLSocket instances must to created with wrap_socket(). In earlier versions, it was possible to create instances directly. This was never documented or officially supported.

SSL sockets also have the following additional methods and attributes:

SSLSocket.read(len=1024, buffer=None)

Read up to len bytes of data from the SSL socket and return the result as a bytes instance. If buffer is specified, then read into the buffer instead, and return the number of bytes read.

Raise SSLWantReadError or SSLWantWriteError if the socket is non-blocking and the read would block.

As at any time a re-negotiation is possible, a call to read() can also cause write operations.

在 3.5 版更改: The socket timeout is no more reset each time bytes are received or sent. The socket timeout is now to maximum total duration to read up to len bytes.

3.6 版后已移除: Use recv() instead of read().

SSLSocket.write(buf)

Write buf to the SSL socket and return the number of bytes written. The buf argument must be an object supporting the buffer interface.

Raise SSLWantReadError or SSLWantWriteError if the socket is non-blocking and the write would block.

As at any time a re-negotiation is possible, a call to write() can also cause read operations.

在 3.5 版更改: The socket timeout is no more reset each time bytes are received or sent. The socket timeout is now to maximum total duration to write buf.

3.6 版后已移除: Use send() instead of write().

注解

The read() and write() methods are the low-level methods that read and write unencrypted, application-level data and decrypt/encrypt it to encrypted, wire-level data. These methods require an active SSL connection, i.e. the handshake was completed and SSLSocket.unwrap() was not called.

Normally you should use the socket API methods like recv() and send() instead of these methods.

SSLSocket.do_handshake()

Perform the SSL setup handshake.

在 3.4 版更改: The handshake method also performs match_hostname() when the check_hostname attribute of the socket's context is true.

在 3.5 版更改: The socket timeout is no more reset each time bytes are received or sent. The socket timeout is now to maximum total duration of the handshake.

在 3.7 版更改: Hostname or IP address is matched by OpenSSL during handshake. The function match_hostname() is no longer used. In case OpenSSL refuses a hostname or IP address, the handshake is aborted early and a TLS alert message is send to the peer.

SSLSocket.getpeercert(binary_form=False)

If there is no certificate for the peer on the other end of the connection, return None. If the SSL handshake hasn't been done yet, raise ValueError.

If the binary_form parameter is False, and a certificate was received from the peer, this method returns a dict instance. If the certificate was not validated, the dict is empty. If the certificate was validated, it returns a dict with several keys, amongst them subject (the principal for which the certificate was issued) and issuer (the principal issuing the certificate). If a certificate contains an instance of the Subject Alternative Name extension (see RFC 3280), there will also be a subjectAltName key in the dictionary.

The subject and issuer fields are tuples containing the sequence of relative distinguished names (RDNs) given in the certificate's data structure for the respective fields, and each RDN is a sequence of name-value pairs. Here is a real-world example:

{'issuer': ((('countryName', 'IL'),),
            (('organizationName', 'StartCom Ltd.'),),
            (('organizationalUnitName',
              'Secure Digital Certificate Signing'),),
            (('commonName',
              'StartCom Class 2 Primary Intermediate Server CA'),)),
 'notAfter': 'Nov 22 08:15:19 2013 GMT',
 'notBefore': 'Nov 21 03:09:52 2011 GMT',
 'serialNumber': '95F0',
 'subject': ((('description', '571208-SLe257oHY9fVQ07Z'),),
             (('countryName', 'US'),),
             (('stateOrProvinceName', 'California'),),
             (('localityName', 'San Francisco'),),
             (('organizationName', 'Electronic Frontier Foundation, Inc.'),),
             (('commonName', '*.eff.org'),),
             (('emailAddress', 'hostmaster@eff.org'),)),
 'subjectAltName': (('DNS', '*.eff.org'), ('DNS', 'eff.org')),
 'version': 3}

注解

To validate a certificate for a particular service, you can use the match_hostname() function.

If the binary_form parameter is True, and a certificate was provided, this method returns the DER-encoded form of the entire certificate as a sequence of bytes, or None if the peer did not provide a certificate. Whether the peer provides a certificate depends on the SSL socket's role:

• for a client SSL socket, the server will always provide a certificate, regardless of whether validation was required;

• for a server SSL socket, the client will only provide a certificate when requested by the server; therefore getpeercert() will return None if you used CERT_NONE (rather than CERT_OPTIONAL or CERT_REQUIRED).

在 3.2 版更改: The returned dictionary includes additional items such as issuer and notBefore.

在 3.4 版更改: ValueError is raised when the handshake isn't done. The returned dictionary includes additional X509v3 extension items such as crlDistributionPoints, caIssuers and OCSP URIs.

在 3.9 版更改: IPv6 address strings no longer have a trailing new line.

SSLSocket.cipher()

Returns a three-value tuple containing the name of the cipher being used, the version of the SSL protocol that defines its use, and the number of secret bits being used. If no connection has been established, returns None.

SSLSocket.shared_ciphers()

Return the list of ciphers shared by the client during the handshake. Each entry of the returned list is a three-value tuple containing the name of the cipher, the version of the SSL protocol that defines its use, and the number of secret bits the cipher uses. shared_ciphers() returns None if no connection has been established or the socket is a client socket.

3.5 新版功能.

SSLSocket.compression()

Return the compression algorithm being used as a string, or None if the connection isn't compressed.

If the higher-level protocol supports its own compression mechanism, you can use OP_NO_COMPRESSION to disable SSL-level compression.

3.3 新版功能.

SSLSocket.get_channel_binding(cb_type="tls-unique")

Get channel binding data for current connection, as a bytes object. Returns None if not connected or the handshake has not been completed.

The cb_type parameter allow selection of the desired channel binding type. Valid channel binding types are listed in the CHANNEL_BINDING_TYPES list. Currently only the 'tls-unique' channel binding, defined by RFC 5929, is supported. ValueError will be raised if an unsupported channel binding type is requested.

3.3 新版功能.

SSLSocket.selected_alpn_protocol()

Return the protocol that was selected during the TLS handshake. If SSLContext.set_alpn_protocols() was not called, if the other party does not support ALPN, if this socket does not support any of the client's proposed protocols, or if the handshake has not happened yet, None is returned.

3.5 新版功能.

SSLSocket.selected_npn_protocol()

Return the higher-level protocol that was selected during the TLS/SSL handshake. If SSLContext.set_npn_protocols() was not called, or if the other party does not support NPN, or if the handshake has not yet happened, this will return None.

3.3 新版功能.

SSLSocket.unwrap()

Performs the SSL shutdown handshake, which removes the TLS layer from the underlying socket, and returns the underlying socket object. This can be used to go from encrypted operation over a connection to unencrypted. The returned socket should always be used for further communication with the other side of the connection, rather than the original socket.

SSLSocket.verify_client_post_handshake()

Requests post-handshake authentication (PHA) from a TLS 1.3 client. PHA can only be initiated for a TLS 1.3 connection from a server-side socket, after the initial TLS handshake and with PHA enabled on both sides, see SSLContext.post_handshake_auth.

The method does not perform a cert exchange immediately. The server-side sends a CertificateRequest during the next write event and expects the client to respond with a certificate on the next read event.

If any precondition isn't met (e.g. not TLS 1.3, PHA not enabled), an SSLError is raised.

注解

Only available with OpenSSL 1.1.1 and TLS 1.3 enabled. Without TLS 1.3 support, the method raises NotImplementedError.

3.8 新版功能.

SSLSocket.version()

Return the actual SSL protocol version negotiated by the connection as a string, or None is no secure connection is established. As of this writing, possible return values include "SSLv2", "SSLv3", "TLSv1", "TLSv1.1" and "TLSv1.2". Recent OpenSSL versions may define more return values.

3.5 新版功能.

SSLSocket.pending()

Returns the number of already decrypted bytes available for read, pending on the connection.

SSLSocket.context

The SSLContext object this SSL socket is tied to. If the SSL socket was created using the deprecated wrap_socket() function (rather than SSLContext.wrap_socket()), this is a custom context object created for this SSL socket.

3.2 新版功能.

SSLSocket.server_side

A boolean which is True for server-side sockets and False for client-side sockets.

3.2 新版功能.

SSLSocket.server_hostname

Hostname of the server: str type, or None for server-side socket or if the hostname was not specified in the constructor.

3.2 新版功能.

在 3.7 版更改: The attribute is now always ASCII text. When server_hostname is an internationalized domain name (IDN), this attribute now stores the A-label form ("xn--pythn-mua.org"), rather than the U-label form ("pythön.org").

SSLSocket.session

The SSLSession for this SSL connection. The session is available for client and server side sockets after the TLS handshake has been performed. For client sockets the session can be set before do_handshake() has been called to reuse a session.

3.6 新版功能.

SSLSocket.session_reused

3.6 新版功能.

SSL Contexts

3.2 新版功能.

An SSL context holds various data longer-lived than single SSL connections, such as SSL configuration options, certificate(s) and private key(s). It also manages a cache of SSL sessions for server-side sockets, in order to speed up repeated connections from the same clients.

class ssl.SSLContext(protocol=PROTOCOL_TLS)

Create a new SSL context. You may pass protocol which must be one of the PROTOCOL_* constants defined in this module. The parameter specifies which version of the SSL protocol to use. Typically, the server chooses a particular protocol version, and the client must adapt to the server's choice. Most of the versions are not interoperable with the other versions. If not specified, the default is PROTOCOL_TLS; it provides the most compatibility with other versions.

Here's a table showing which versions in a client (down the side) can connect to which versions in a server (along the top):

客户端 / 服务器	SSLv2	SSLv3	TLS 3	TLSv1	TLSv1.1	TLSv1.2
SSLv2	是	否	否 1	否	否	否
SSLv3	否	是	否 2	否	否	否
TLS (SSLv23) 3	否 1	否 2	是	是	是	是
TLSv1	否	否	是	是	否	否
TLSv1.1	否	否	是	否	是	否
TLSv1.2	否	否	是	否	否	是

脚注

1(1,2)

SSLContext disables SSLv2 with OP_NO_SSLv2 by default.

2(1,2)

SSLContext disables SSLv3 with OP_NO_SSLv3 by default.

3(1,2)

TLS 1.3 protocol will be available with PROTOCOL_TLS in OpenSSL >= 1.1.1. There is no dedicated PROTOCOL constant for just TLS 1.3.

参见

create_default_context() lets the ssl module choose security settings for a given purpose.

在 3.6 版更改: The context is created with secure default values. The options OP_NO_COMPRESSION, OP_CIPHER_SERVER_PREFERENCE, OP_SINGLE_DH_USE, OP_SINGLE_ECDH_USE, OP_NO_SSLv2 (except for PROTOCOL_SSLv2), and OP_NO_SSLv3 (except for PROTOCOL_SSLv3) are set by default. The initial cipher suite list contains only HIGH ciphers, no NULL ciphers and no MD5 ciphers (except for PROTOCOL_SSLv2).

SSLContext objects have the following methods and attributes:

SSLContext.cert_store_stats()

Get statistics about quantities of loaded X.509 certificates, count of X.509 certificates flagged as CA certificates and certificate revocation lists as dictionary.

Example for a context with one CA cert and one other cert:

>>> context.cert_store_stats()
{'crl': 0, 'x509_ca': 1, 'x509': 2}

3.4 新版功能.

SSLContext.load_cert_chain(certfile, keyfile=None, password=None)

Load a private key and the corresponding certificate. The certfile string must be the path to a single file in PEM format containing the certificate as well as any number of CA certificates needed to establish the certificate's authenticity. The keyfile string, if present, must point to a file containing the private key in. Otherwise the private key will be taken from certfile as well. See the discussion of Certificates for more information on how the certificate is stored in the certfile.

The password argument may be a function to call to get the password for decrypting the private key. It will only be called if the private key is encrypted and a password is necessary. It will be called with no arguments, and it should return a string, bytes, or bytearray. If the return value is a string it will be encoded as UTF-8 before using it to decrypt the key. Alternatively a string, bytes, or bytearray value may be supplied directly as the password argument. It will be ignored if the private key is not encrypted and no password is needed.

If the password argument is not specified and a password is required, OpenSSL's built-in password prompting mechanism will be used to interactively prompt the user for a password.

An SSLError is raised if the private key doesn't match with the certificate.

在 3.3 版更改: New optional argument password.

SSLContext.load_default_certs(purpose=Purpose.SERVER_AUTH)

Load a set of default "certification authority" (CA) certificates from default locations. On Windows it loads CA certs from the CA and ROOT system stores. On other systems it calls SSLContext.set_default_verify_paths(). In the future the method may load CA certificates from other locations, too.

The purpose flag specifies what kind of CA certificates are loaded. The default settings Purpose.SERVER_AUTH loads certificates, that are flagged and trusted for TLS web server authentication (client side sockets). Purpose.CLIENT_AUTH loads CA certificates for client certificate verification on the server side.

3.4 新版功能.

SSLContext.load_verify_locations(cafile=None, capath=None, cadata=None)

Load a set of "certification authority" (CA) certificates used to validate other peers' certificates when verify_mode is other than CERT_NONE. At least one of cafile or capath must be specified.

This method can also load certification revocation lists (CRLs) in PEM or DER format. In order to make use of CRLs, SSLContext.verify_flags must be configured properly.

The cafile string, if present, is the path to a file of concatenated CA certificates in PEM format. See the discussion of Certificates for more information about how to arrange the certificates in this file.

The capath string, if present, is the path to a directory containing several CA certificates in PEM format, following an OpenSSL specific layout.

The cadata object, if present, is either an ASCII string of one or more PEM-encoded certificates or a bytes-like object of DER-encoded certificates. Like with capath extra lines around PEM-encoded certificates are ignored but at least one certificate must be present.

在 3.4 版更改: New optional argument cadata

SSLContext.get_ca_certs(binary_form=False)

Get a list of loaded "certification authority" (CA) certificates. If the binary_form parameter is False each list entry is a dict like the output of SSLSocket.getpeercert(). Otherwise the method returns a list of DER-encoded certificates. The returned list does not contain certificates from capath unless a certificate was requested and loaded by a SSL connection.

注解

Certificates in a capath directory aren't loaded unless they have been used at least once.

3.4 新版功能.

SSLContext.get_ciphers()

Get a list of enabled ciphers. The list is in order of cipher priority. See SSLContext.set_ciphers().

示例:

>>> ctx = ssl.SSLContext(ssl.PROTOCOL_SSLv23)
>>> ctx.set_ciphers('ECDHE+AESGCM:!ECDSA')
>>> ctx.get_ciphers()  # OpenSSL 1.0.x
[{'alg_bits': 256,
  'description': 'ECDHE-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH     Au=RSA  '
                 'Enc=AESGCM(256) Mac=AEAD',
  'id': 50380848,
  'name': 'ECDHE-RSA-AES256-GCM-SHA384',
  'protocol': 'TLSv1/SSLv3',
  'strength_bits': 256},
 {'alg_bits': 128,
  'description': 'ECDHE-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=ECDH     Au=RSA  '
                 'Enc=AESGCM(128) Mac=AEAD',
  'id': 50380847,
  'name': 'ECDHE-RSA-AES128-GCM-SHA256',
  'protocol': 'TLSv1/SSLv3',
  'strength_bits': 128}]

On OpenSSL 1.1 and newer the cipher dict contains additional fields:

>>> ctx.get_ciphers()  # OpenSSL 1.1+
[{'aead': True,
  'alg_bits': 256,
  'auth': 'auth-rsa',
  'description': 'ECDHE-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH     Au=RSA  '
                 'Enc=AESGCM(256) Mac=AEAD',
  'digest': None,
  'id': 50380848,
  'kea': 'kx-ecdhe',
  'name': 'ECDHE-RSA-AES256-GCM-SHA384',
  'protocol': 'TLSv1.2',
  'strength_bits': 256,
  'symmetric': 'aes-256-gcm'},
 {'aead': True,
  'alg_bits': 128,
  'auth': 'auth-rsa',
  'description': 'ECDHE-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=ECDH     Au=RSA  '
                 'Enc=AESGCM(128) Mac=AEAD',
  'digest': None,
  'id': 50380847,
  'kea': 'kx-ecdhe',
  'name': 'ECDHE-RSA-AES128-GCM-SHA256',
  'protocol': 'TLSv1.2',
  'strength_bits': 128,
  'symmetric': 'aes-128-gcm'}]

Availability: OpenSSL 1.0.2+.

3.6 新版功能.

SSLContext.set_default_verify_paths()

Load a set of default "certification authority" (CA) certificates from a filesystem path defined when building the OpenSSL library. Unfortunately, there's no easy way to know whether this method succeeds: no error is returned if no certificates are to be found. When the OpenSSL library is provided as part of the operating system, though, it is likely to be configured properly.

SSLContext.set_ciphers(ciphers)

Set the available ciphers for sockets created with this context. It should be a string in the OpenSSL cipher list format. If no cipher can be selected (because compile-time options or other configuration forbids use of all the specified ciphers), an SSLError will be raised.

注解

when connected, the SSLSocket.cipher() method of SSL sockets will give the currently selected cipher.

OpenSSL 1.1.1 has TLS 1.3 cipher suites enabled by default. The suites cannot be disabled with set_ciphers().

SSLContext.set_alpn_protocols(protocols)

Specify which protocols the socket should advertise during the SSL/TLS handshake. It should be a list of ASCII strings, like ['http/1.1', 'spdy/2'], ordered by preference. The selection of a protocol will happen during the handshake, and will play out according to RFC 7301. After a successful handshake, the SSLSocket.selected_alpn_protocol() method will return the agreed-upon protocol.

This method will raise NotImplementedError if HAS_ALPN is False.

OpenSSL 1.1.0 to 1.1.0e will abort the handshake and raise SSLError when both sides support ALPN but cannot agree on a protocol. 1.1.0f+ behaves like 1.0.2, SSLSocket.selected_alpn_protocol() returns None.

3.5 新版功能.

SSLContext.set_npn_protocols(protocols)

Specify which protocols the socket should advertise during the SSL/TLS handshake. It should be a list of strings, like ['http/1.1', 'spdy/2'], ordered by preference. The selection of a protocol will happen during the handshake, and will play out according to the Application Layer Protocol Negotiation. After a successful handshake, the SSLSocket.selected_npn_protocol() method will return the agreed-upon protocol.

This method will raise NotImplementedError if HAS_NPN is False.

3.3 新版功能.

SSLContext.sni_callback

Register a callback function that will be called after the TLS Client Hello handshake message has been received by the SSL/TLS server when the TLS client specifies a server name indication. The server name indication mechanism is specified in RFC 6066 section 3 - Server Name Indication.

Only one callback can be set per SSLContext. If sni_callback is set to None then the callback is disabled. Calling this function a subsequent time will disable the previously registered callback.

The callback function will be called with three arguments; the first being the ssl.SSLSocket, the second is a string that represents the server name that the client is intending to communicate (or None if the TLS Client Hello does not contain a server name) and the third argument is the original SSLContext. The server name argument is text. For internationalized domain name, the server name is an IDN A-label ("xn--pythn-mua.org").

A typical use of this callback is to change the ssl.SSLSocket's SSLSocket.context attribute to a new object of type SSLContext representing a certificate chain that matches the server name.

Due to the early negotiation phase of the TLS connection, only limited methods and attributes are usable like SSLSocket.selected_alpn_protocol() and SSLSocket.context. SSLSocket.getpeercert(), SSLSocket.getpeercert(), SSLSocket.cipher() and SSLSocket.compress() methods require that the TLS connection has progressed beyond the TLS Client Hello and therefore will not contain return meaningful values nor can they be called safely.

The sni_callback function must return None to allow the TLS negotiation to continue. If a TLS failure is required, a constant ALERT_DESCRIPTION_* can be returned. Other return values will result in a TLS fatal error with ALERT_DESCRIPTION_INTERNAL_ERROR.

If an exception is raised from the sni_callback function the TLS connection will terminate with a fatal TLS alert message ALERT_DESCRIPTION_HANDSHAKE_FAILURE.

This method will raise NotImplementedError if the OpenSSL library had OPENSSL_NO_TLSEXT defined when it was built.

3.7 新版功能.

SSLContext.set_servername_callback(server_name_callback)

This is a legacy API retained for backwards compatibility. When possible, you should use sni_callback instead. The given server_name_callback is similar to sni_callback, except that when the server hostname is an IDN-encoded internationalized domain name, the server_name_callback receives a decoded U-label ("pythön.org").

If there is an decoding error on the server name, the TLS connection will terminate with an ALERT_DESCRIPTION_INTERNAL_ERROR fatal TLS alert message to the client.

3.4 新版功能.

SSLContext.load_dh_params(dhfile)

Load the key generation parameters for Diffie-Hellman (DH) key exchange. Using DH key exchange improves forward secrecy at the expense of computational resources (both on the server and on the client). The dhfile parameter should be the path to a file containing DH parameters in PEM format.

This setting doesn't apply to client sockets. You can also use the OP_SINGLE_DH_USE option to further improve security.

3.3 新版功能.

SSLContext.set_ecdh_curve(curve_name)

Set the curve name for Elliptic Curve-based Diffie-Hellman (ECDH) key exchange. ECDH is significantly faster than regular DH while arguably as secure. The curve_name parameter should be a string describing a well-known elliptic curve, for example prime256v1 for a widely supported curve.

This setting doesn't apply to client sockets. You can also use the OP_SINGLE_ECDH_USE option to further improve security.

This method is not available if HAS_ECDH is False.

3.3 新版功能.

参见

SSL/TLS & Perfect Forward Secrecy

Vincent Bernat.

SSLContext.wrap_socket(sock, server_side=False, do_handshake_on_connect=True, suppress_ragged_eofs=True, server_hostname=None, session=None)

Wrap an existing Python socket sock and return an instance of SSLContext.sslsocket_class (default SSLSocket). The returned SSL socket is tied to the context, its settings and certificates. sock must be a SOCK_STREAM socket; other socket types are unsupported.

The parameter server_side is a boolean which identifies whether server-side or client-side behavior is desired from this socket.

For client-side sockets, the context construction is lazy; if the underlying socket isn't connected yet, the context construction will be performed after connect() is called on the socket. For server-side sockets, if the socket has no remote peer, it is assumed to be a listening socket, and the server-side SSL wrapping is automatically performed on client connections accepted via the accept() method. The method may raise SSLError.

On client connections, the optional parameter server_hostname specifies the hostname of the service which we are connecting to. This allows a single server to host multiple SSL-based services with distinct certificates, quite similarly to HTTP virtual hosts. Specifying server_hostname will raise a ValueError if server_side is true.

The parameter do_handshake_on_connect specifies whether to do the SSL handshake automatically after doing a socket.connect(), or whether the application program will call it explicitly, by invoking the SSLSocket.do_handshake() method. Calling SSLSocket.do_handshake() explicitly gives the program control over the blocking behavior of the socket I/O involved in the handshake.

The parameter suppress_ragged_eofs specifies how the SSLSocket.recv() method should signal unexpected EOF from the other end of the connection. If specified as True (the default), it returns a normal EOF (an empty bytes object) in response to unexpected EOF errors raised from the underlying socket; if False, it will raise the exceptions back to the caller.

session, see session.

在 3.5 版更改: Always allow a server_hostname to be passed, even if OpenSSL does not have SNI.

在 3.6 版更改: session argument was added.

在 3.7 版更改: The method returns on instance of SSLContext.sslsocket_class instead of hard-coded SSLSocket.

SSLContext.sslsocket_class

The return type of SSLContext.wrap_socket(), defaults to SSLSocket. The attribute can be overridden on instance of class in order to return a custom subclass of SSLSocket.

3.7 新版功能.

SSLContext.wrap_bio(incoming, outgoing, server_side=False, server_hostname=None, session=None)

Wrap the BIO objects incoming and outgoing and return an instance of SSLContext.sslobject_class (default SSLObject). The SSL routines will read input data from the incoming BIO and write data to the outgoing BIO.

The server_side, server_hostname and session parameters have the same meaning as in SSLContext.wrap_socket().

在 3.6 版更改: session argument was added.

在 3.7 版更改: The method returns on instance of SSLContext.sslobject_class instead of hard-coded SSLObject.

SSLContext.sslobject_class

The return type of SSLContext.wrap_bio(), defaults to SSLObject. The attribute can be overridden on instance of class in order to return a custom subclass of SSLObject.

3.7 新版功能.

SSLContext.session_stats()

Get statistics about the SSL sessions created or managed by this context. A dictionary is returned which maps the names of each piece of information to their numeric values. For example, here is the total number of hits and misses in the session cache since the context was created:

>>> stats = context.session_stats()
>>> stats['hits'], stats['misses']
(0, 0)

SSLContext.check_hostname

Whether to match the peer cert's hostname with match_hostname() in SSLSocket.do_handshake(). The context's verify_mode must be set to CERT_OPTIONAL or CERT_REQUIRED, and you must pass server_hostname to wrap_socket() in order to match the hostname. Enabling hostname checking automatically sets verify_mode from CERT_NONE to CERT_REQUIRED. It cannot be set back to CERT_NONE as long as hostname checking is enabled. The PROTOCOL_TLS_CLIENT protocol enables hostname checking by default. With other protocols, hostname checking must be enabled explicitly.

示例:

import socket, ssl

context = ssl.SSLContext(ssl.PROTOCOL_TLSv1_2)
context.verify_mode = ssl.CERT_REQUIRED
context.check_hostname = True
context.load_default_certs()

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
ssl_sock = context.wrap_socket(s, server_hostname='www.verisign.com')
ssl_sock.connect(('www.verisign.com', 443))

3.4 新版功能.

在 3.7 版更改: verify_mode is now automatically changed to CERT_REQUIRED when hostname checking is enabled and verify_mode is CERT_NONE. Previously the same operation would have failed with a ValueError.

注解

This features requires OpenSSL 0.9.8f or newer.

SSLContext.keylog_filename

Write TLS keys to a keylog file, whenever key material is generated or received. The keylog file is designed for debugging purposes only. The file format is specified by NSS and used by many traffic analyzers such as Wireshark. The log file is opened in append-only mode. Writes are synchronized between threads, but not between processes.

3.8 新版功能.

注解

This features requires OpenSSL 1.1.1 or newer.

SSLContext.maximum_version

A TLSVersion enum member representing the highest supported TLS version. The value defaults to TLSVersion.MAXIMUM_SUPPORTED. The attribute is read-only for protocols other than PROTOCOL_TLS, PROTOCOL_TLS_CLIENT, and PROTOCOL_TLS_SERVER.

The attributes maximum_version, minimum_version and SSLContext.options all affect the supported SSL and TLS versions of the context. The implementation does not prevent invalid combination. For example a context with OP_NO_TLSv1_2 in options and maximum_version set to TLSVersion.TLSv1_2 will not be able to establish a TLS 1.2 connection.

注解

This attribute is not available unless the ssl module is compiled with OpenSSL 1.1.0g or newer.

3.7 新版功能.

SSLContext.minimum_version

Like SSLContext.maximum_version except it is the lowest supported version or TLSVersion.MINIMUM_SUPPORTED.

注解

This attribute is not available unless the ssl module is compiled with OpenSSL 1.1.0g or newer.

3.7 新版功能.

SSLContext.num_tickets

Control the number of TLS 1.3 session tickets of a TLS_PROTOCOL_SERVER context. The setting has no impact on TLS 1.0 to 1.2 connections.

注解

This attribute is not available unless the ssl module is compiled with OpenSSL 1.1.1 or newer.

3.8 新版功能.

SSLContext.options

An integer representing the set of SSL options enabled on this context. The default value is OP_ALL, but you can specify other options such as OP_NO_SSLv2 by ORing them together.

注解

With versions of OpenSSL older than 0.9.8m, it is only possible to set options, not to clear them. Attempting to clear an option (by resetting the corresponding bits) will raise a ValueError.

在 3.6 版更改: SSLContext.options returns Options flags:

>>> ssl.create_default_context().options  
<Options.OP_ALL|OP_NO_SSLv3|OP_NO_SSLv2|OP_NO_COMPRESSION: 2197947391>

SSLContext.post_handshake_auth

Enable TLS 1.3 post-handshake client authentication. Post-handshake auth is disabled by default and a server can only request a TLS client certificate during the initial handshake. When enabled, a server may request a TLS client certificate at any time after the handshake.

When enabled on client-side sockets, the client signals the server that it supports post-handshake authentication.

When enabled on server-side sockets, SSLContext.verify_mode must be set to CERT_OPTIONAL or CERT_REQUIRED, too. The actual client cert exchange is delayed until SSLSocket.verify_client_post_handshake() is called and some I/O is performed.

注解

Only available with OpenSSL 1.1.1 and TLS 1.3 enabled. Without TLS 1.3 support, the property value is None and can't be modified

3.8 新版功能.

SSLContext.protocol

The protocol version chosen when constructing the context. This attribute is read-only.

SSLContext.hostname_checks_common_name

Whether check_hostname falls back to verify the cert's subject common name in the absence of a subject alternative name extension (default: true).

注解

Only writeable with OpenSSL 1.1.0 or higher.

3.7 新版功能.

SSLContext.verify_flags

The flags for certificate verification operations. You can set flags like VERIFY_CRL_CHECK_LEAF by ORing them together. By default OpenSSL does neither require nor verify certificate revocation lists (CRLs). Available only with openssl version 0.9.8+.

3.4 新版功能.

在 3.6 版更改: SSLContext.verify_flags returns VerifyFlags flags:

>>> ssl.create_default_context().verify_flags  
<VerifyFlags.VERIFY_X509_TRUSTED_FIRST: 32768>

SSLContext.verify_mode

Whether to try to verify other peers' certificates and how to behave if verification fails. This attribute must be one of CERT_NONE, CERT_OPTIONAL or CERT_REQUIRED.

在 3.6 版更改: SSLContext.verify_mode returns VerifyMode enum:

>>> ssl.create_default_context().verify_mode
<VerifyMode.CERT_REQUIRED: 2>

Certificates

Certificates in general are part of a public-key / private-key system. In this system, each principal, (which may be a machine, or a person, or an organization) is assigned a unique two-part encryption key. One part of the key is public, and is called the public key; the other part is kept secret, and is called the private key. The two parts are related, in that if you encrypt a message with one of the parts, you can decrypt it with the other part, and only with the other part.

A certificate contains information about two principals. It contains the name of a subject, and the subject's public key. It also contains a statement by a second principal, the issuer, that the subject is who they claim to be, and that this is indeed the subject's public key. The issuer's statement is signed with the issuer's private key, which only the issuer knows. However, anyone can verify the issuer's statement by finding the issuer's public key, decrypting the statement with it, and comparing it to the other information in the certificate. The certificate also contains information about the time period over which it is valid. This is expressed as two fields, called "notBefore" and "notAfter".

In the Python use of certificates, a client or server can use a certificate to prove who they are. The other side of a network connection can also be required to produce a certificate, and that certificate can be validated to the satisfaction of the client or server that requires such validation. The connection attempt can be set to raise an exception if the validation fails. Validation is done automatically, by the underlying OpenSSL framework; the application need not concern itself with its mechanics. But the application does usually need to provide sets of certificates to allow this process to take place.

Python uses files to contain certificates. They should be formatted as "PEM" (see RFC 1422), which is a base-64 encoded form wrapped with a header line and a footer line:

-----BEGIN CERTIFICATE-----
... (certificate in base64 PEM encoding) ...
-----END CERTIFICATE-----

Certificate chains

The Python files which contain certificates can contain a sequence of certificates, sometimes called a certificate chain. This chain should start with the specific certificate for the principal who "is" the client or server, and then the certificate for the issuer of that certificate, and then the certificate for the issuer of that certificate, and so on up the chain till you get to a certificate which is self-signed, that is, a certificate which has the same subject and issuer, sometimes called a root certificate. The certificates should just be concatenated together in the certificate file. For example, suppose we had a three certificate chain, from our server certificate to the certificate of the certification authority that signed our server certificate, to the root certificate of the agency which issued the certification authority's certificate:

-----BEGIN CERTIFICATE-----
... (certificate for your server)...
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
... (the certificate for the CA)...
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
... (the root certificate for the CA's issuer)...
-----END CERTIFICATE-----

CA certificates

If you are going to require validation of the other side of the connection's certificate, you need to provide a "CA certs" file, filled with the certificate chains for each issuer you are willing to trust. Again, this file just contains these chains concatenated together. For validation, Python will use the first chain it finds in the file which matches. The platform's certificates file can be used by calling SSLContext.load_default_certs(), this is done automatically with create_default_context().

Combined key and certificate

Often the private key is stored in the same file as the certificate; in this case, only the certfile parameter to SSLContext.load_cert_chain() and wrap_socket() needs to be passed. If the private key is stored with the certificate, it should come before the first certificate in the certificate chain:

-----BEGIN RSA PRIVATE KEY-----
... (private key in base64 encoding) ...
-----END RSA PRIVATE KEY-----
-----BEGIN CERTIFICATE-----
... (certificate in base64 PEM encoding) ...
-----END CERTIFICATE-----

Self-signed certificates

If you are going to create a server that provides SSL-encrypted connection services, you will need to acquire a certificate for that service. There are many ways of acquiring appropriate certificates, such as buying one from a certification authority. Another common practice is to generate a self-signed certificate. The simplest way to do this is with the OpenSSL package, using something like the following:

% openssl req -new -x509 -days 365 -nodes -out cert.pem -keyout cert.pem
Generating a 1024 bit RSA private key
.......++++++
.............................++++++
writing new private key to 'cert.pem'
-----
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [AU]:US
State or Province Name (full name) [Some-State]:MyState
Locality Name (eg, city) []:Some City
Organization Name (eg, company) [Internet Widgits Pty Ltd]:My Organization, Inc.
Organizational Unit Name (eg, section) []:My Group
Common Name (eg, YOUR name) []:myserver.mygroup.myorganization.com
Email Address []:ops@myserver.mygroup.myorganization.com
%

The disadvantage of a self-signed certificate is that it is its own root certificate, and no one else will have it in their cache of known (and trusted) root certificates.

示例

Testing for SSL support

To test for the presence of SSL support in a Python installation, user code should use the following idiom:

try:
    import ssl
except ImportError:
    pass
else:
    ...  # do something that requires SSL support

Client-side operation

This example creates a SSL context with the recommended security settings for client sockets, including automatic certificate verification:

>>> context = ssl.create_default_context()

If you prefer to tune security settings yourself, you might create a context from scratch (but beware that you might not get the settings right):

>>> context = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
>>> context.load_verify_locations("/etc/ssl/certs/ca-bundle.crt")

(this snippet assumes your operating system places a bundle of all CA certificates in /etc/ssl/certs/ca-bundle.crt; if not, you'll get an error and have to adjust the location)

The PROTOCOL_TLS_CLIENT protocol configures the context for cert validation and hostname verification. verify_mode is set to CERT_REQUIRED and check_hostname is set to True. All other protocols create SSL contexts with insecure defaults.

When you use the context to connect to a server, CERT_REQUIRED and check_hostname validate the server certificate: it ensures that the server certificate was signed with one of the CA certificates, checks the signature for correctness, and verifies other properties like validity and identity of the hostname:

>>> conn = context.wrap_socket(socket.socket(socket.AF_INET),
...                            server_hostname="www.python.org")
>>> conn.connect(("www.python.org", 443))

You may then fetch the certificate:

>>> cert = conn.getpeercert()

Visual inspection shows that the certificate does identify the desired service (that is, the HTTPS host www.python.org):

>>> pprint.pprint(cert)
{'OCSP': ('http://ocsp.digicert.com',),
 'caIssuers': ('http://cacerts.digicert.com/DigiCertSHA2ExtendedValidationServerCA.crt',),
 'crlDistributionPoints': ('http://crl3.digicert.com/sha2-ev-server-g1.crl',
                           'http://crl4.digicert.com/sha2-ev-server-g1.crl'),
 'issuer': ((('countryName', 'US'),),
            (('organizationName', 'DigiCert Inc'),),
            (('organizationalUnitName', 'www.digicert.com'),),
            (('commonName', 'DigiCert SHA2 Extended Validation Server CA'),)),
 'notAfter': 'Sep  9 12:00:00 2016 GMT',
 'notBefore': 'Sep  5 00:00:00 2014 GMT',
 'serialNumber': '01BB6F00122B177F36CAB49CEA8B6B26',
 'subject': ((('businessCategory', 'Private Organization'),),
             (('1.3.6.1.4.1.311.60.2.1.3', 'US'),),
             (('1.3.6.1.4.1.311.60.2.1.2', 'Delaware'),),
             (('serialNumber', '3359300'),),
             (('streetAddress', '16 Allen Rd'),),
             (('postalCode', '03894-4801'),),
             (('countryName', 'US'),),
             (('stateOrProvinceName', 'NH'),),
             (('localityName', 'Wolfeboro'),),
             (('organizationName', 'Python Software Foundation'),),
             (('commonName', 'www.python.org'),)),
 'subjectAltName': (('DNS', 'www.python.org'),
                    ('DNS', 'python.org'),
                    ('DNS', 'pypi.org'),
                    ('DNS', 'docs.python.org'),
                    ('DNS', 'testpypi.org'),
                    ('DNS', 'bugs.python.org'),
                    ('DNS', 'wiki.python.org'),
                    ('DNS', 'hg.python.org'),
                    ('DNS', 'mail.python.org'),
                    ('DNS', 'packaging.python.org'),
                    ('DNS', 'pythonhosted.org'),
                    ('DNS', 'www.pythonhosted.org'),
                    ('DNS', 'test.pythonhosted.org'),
                    ('DNS', 'us.pycon.org'),
                    ('DNS', 'id.python.org')),
 'version': 3}

Now the SSL channel is established and the certificate verified, you can proceed to talk with the server:

>>> conn.sendall(b"HEAD / HTTP/1.0\r\nHost: linuxfr.org\r\n\r\n")
>>> pprint.pprint(conn.recv(1024).split(b"\r\n"))
[b'HTTP/1.1 200 OK',
 b'Date: Sat, 18 Oct 2014 18:27:20 GMT',
 b'Server: nginx',
 b'Content-Type: text/html; charset=utf-8',
 b'X-Frame-Options: SAMEORIGIN',
 b'Content-Length: 45679',
 b'Accept-Ranges: bytes',
 b'Via: 1.1 varnish',
 b'Age: 2188',
 b'X-Served-By: cache-lcy1134-LCY',
 b'X-Cache: HIT',
 b'X-Cache-Hits: 11',
 b'Vary: Cookie',
 b'Strict-Transport-Security: max-age=63072000; includeSubDomains',
 b'Connection: close',
 b'',
 b'']

See the discussion of Security considerations below.

Server-side operation

For server operation, typically you'll need to have a server certificate, and private key, each in a file. You'll first create a context holding the key and the certificate, so that clients can check your authenticity. Then you'll open a socket, bind it to a port, call listen() on it, and start waiting for clients to connect:

import socket, ssl

context = ssl.create_default_context(ssl.Purpose.CLIENT_AUTH)
context.load_cert_chain(certfile="mycertfile", keyfile="mykeyfile")

bindsocket = socket.socket()
bindsocket.bind(('myaddr.mydomain.com', 10023))
bindsocket.listen(5)

When a client connects, you'll call accept() on the socket to get the new socket from the other end, and use the context's SSLContext.wrap_socket() method to create a server-side SSL socket for the connection:

while True:
    newsocket, fromaddr = bindsocket.accept()
    connstream = context.wrap_socket(newsocket, server_side=True)
    try:
        deal_with_client(connstream)
    finally:
        connstream.shutdown(socket.SHUT_RDWR)
        connstream.close()

Then you'll read data from the connstream and do something with it till you are finished with the client (or the client is finished with you):

def deal_with_client(connstream):
    data = connstream.recv(1024)
    # empty data means the client is finished with us
    while data:
        if not do_something(connstream, data):
            # we'll assume do_something returns False
            # when we're finished with client
            break
        data = connstream.recv(1024)
    # finished with client

And go back to listening for new client connections (of course, a real server would probably handle each client connection in a separate thread, or put the sockets in non-blocking mode and use an event loop).

Notes on non-blocking sockets

SSL sockets behave slightly different than regular sockets in non-blocking mode. When working with non-blocking sockets, there are thus several things you need to be aware of:

• Most SSLSocket methods will raise either SSLWantWriteError or SSLWantReadError instead of BlockingIOError if an I/O operation would block. SSLWantReadError will be raised if a read operation on the underlying socket is necessary, and SSLWantWriteError for a write operation on the underlying socket. Note that attempts to write to an SSL socket may require reading from the underlying socket first, and attempts to read from the SSL socket may require a prior write to the underlying socket.

  在 3.5 版更改: In earlier Python versions, the SSLSocket.send() method returned zero instead of raising SSLWantWriteError or SSLWantReadError.

• Calling select() tells you that the OS-level socket can be read from (or written to), but it does not imply that there is sufficient data at the upper SSL layer. For example, only part of an SSL frame might have arrived. Therefore, you must be ready to handle SSLSocket.recv() and SSLSocket.send() failures, and retry after another call to select().

• Conversely, since the SSL layer has its own framing, a SSL socket may still have data available for reading without select() being aware of it. Therefore, you should first call SSLSocket.recv() to drain any potentially available data, and then only block on a select() call if still necessary.

  (of course, similar provisions apply when using other primitives such as poll(), or those in the selectors module)

• The SSL handshake itself will be non-blocking: the SSLSocket.do_handshake() method has to be retried until it returns successfully. Here is a synopsis using select() to wait for the socket's readiness:

  while True:
      try:
          sock.do_handshake()
          break
      except ssl.SSLWantReadError:
          select.select([sock], [], [])
      except ssl.SSLWantWriteError:
          select.select([], [sock], [])
  

参见

The asyncio module supports non-blocking SSL sockets and provides a higher level API. It polls for events using the selectors module and handles SSLWantWriteError, SSLWantReadError and BlockingIOError exceptions. It runs the SSL handshake asynchronously as well.

Memory BIO Support

3.5 新版功能.

Ever since the SSL module was introduced in Python 2.6, the SSLSocket class has provided two related but distinct areas of functionality:

• SSL protocol handling

• Network IO

The network IO API is identical to that provided by socket.socket, from which SSLSocket also inherits. This allows an SSL socket to be used as a drop-in replacement for a regular socket, making it very easy to add SSL support to an existing application.

Combining SSL protocol handling and network IO usually works well, but there are some cases where it doesn't. An example is async IO frameworks that want to use a different IO multiplexing model than the "select/poll on a file descriptor" (readiness based) model that is assumed by socket.socket and by the internal OpenSSL socket IO routines. This is mostly relevant for platforms like Windows where this model is not efficient. For this purpose, a reduced scope variant of SSLSocket called SSLObject is provided.

class ssl.SSLObject

A reduced-scope variant of SSLSocket representing an SSL protocol instance that does not contain any network IO methods. This class is typically used by framework authors that want to implement asynchronous IO for SSL through memory buffers.

This class implements an interface on top of a low-level SSL object as implemented by OpenSSL. This object captures the state of an SSL connection but does not provide any network IO itself. IO needs to be performed through separate "BIO" objects which are OpenSSL's IO abstraction layer.

This class has no public constructor. An SSLObject instance must be created using the wrap_bio() method. This method will create the SSLObject instance and bind it to a pair of BIOs. The incoming BIO is used to pass data from Python to the SSL protocol instance, while the outgoing BIO is used to pass data the other way around.

可以使用以下方法：

• context

• server_side

• server_hostname

• session

• session_reused

• read()

• write()

• getpeercert()

• selected_alpn_protocol()

• selected_npn_protocol()

• cipher()

• shared_ciphers()

• compression()

• pending()

• do_handshake()

• verify_client_post_handshake()

• unwrap()

• get_channel_binding()

• version()

When compared to SSLSocket, this object lacks the following features:

• Any form of network IO; recv() and send() read and write only to the underlying MemoryBIO buffers.

• There is no do_handshake_on_connect machinery. You must always manually call do_handshake() to start the handshake.

• There is no handling of suppress_ragged_eofs. All end-of-file conditions that are in violation of the protocol are reported via the SSLEOFError exception.

• The method unwrap() call does not return anything, unlike for an SSL socket where it returns the underlying socket.

• The server_name_callback callback passed to SSLContext.set_servername_callback() will get an SSLObject instance instead of a SSLSocket instance as its first parameter.

Some notes related to the use of SSLObject:

• All IO on an SSLObject is non-blocking. This means that for example read() will raise an SSLWantReadError if it needs more data than the incoming BIO has available.

• There is no module-level wrap_bio() call like there is for wrap_socket(). An SSLObject is always created via an SSLContext.

在 3.7 版更改: SSLObject instances must to created with wrap_bio(). In earlier versions, it was possible to create instances directly. This was never documented or officially supported.

An SSLObject communicates with the outside world using memory buffers. The class MemoryBIO provides a memory buffer that can be used for this purpose. It wraps an OpenSSL memory BIO (Basic IO) object:

class ssl.MemoryBIO

A memory buffer that can be used to pass data between Python and an SSL protocol instance.

pending

Return the number of bytes currently in the memory buffer.

eof

A boolean indicating whether the memory BIO is current at the end-of-file position.

read(n=-1)

Read up to n bytes from the memory buffer. If n is not specified or negative, all bytes are returned.

write(buf)

Write the bytes from buf to the memory BIO. The buf argument must be an object supporting the buffer protocol.

The return value is the number of bytes written, which is always equal to the length of buf.

write_eof()

Write an EOF marker to the memory BIO. After this method has been called, it is illegal to call write(). The attribute eof will become true after all data currently in the buffer has been read.

SSL session

3.6 新版功能.

class ssl.SSLSession

Session object used by session.

id

time

timeout

ticket_lifetime_hint

has_ticket

Security considerations

Best defaults

For client use, if you don't have any special requirements for your security policy, it is highly recommended that you use the create_default_context() function to create your SSL context. It will load the system's trusted CA certificates, enable certificate validation and hostname checking, and try to choose reasonably secure protocol and cipher settings.

For example, here is how you would use the smtplib.SMTP class to create a trusted, secure connection to a SMTP server:

>>> import ssl, smtplib
>>> smtp = smtplib.SMTP("mail.python.org", port=587)
>>> context = ssl.create_default_context()
>>> smtp.starttls(context=context)
(220, b'2.0.0 Ready to start TLS')

If a client certificate is needed for the connection, it can be added with SSLContext.load_cert_chain().

By contrast, if you create the SSL context by calling the SSLContext constructor yourself, it will not have certificate validation nor hostname checking enabled by default. If you do so, please read the paragraphs below to achieve a good security level.

Manual settings

Verifying certificates

When calling the SSLContext constructor directly, CERT_NONE is the default. Since it does not authenticate the other peer, it can be insecure, especially in client mode where most of time you would like to ensure the authenticity of the server you're talking to. Therefore, when in client mode, it is highly recommended to use CERT_REQUIRED. However, it is in itself not sufficient; you also have to check that the server certificate, which can be obtained by calling SSLSocket.getpeercert(), matches the desired service. For many protocols and applications, the service can be identified by the hostname; in this case, the match_hostname() function can be used. This common check is automatically performed when SSLContext.check_hostname is enabled.

在 3.7 版更改: Hostname matchings is now performed by OpenSSL. Python no longer uses match_hostname().

In server mode, if you want to authenticate your clients using the SSL layer (rather than using a higher-level authentication mechanism), you'll also have to specify CERT_REQUIRED and similarly check the client certificate.

Protocol versions

SSL versions 2 and 3 are considered insecure and are therefore dangerous to use. If you want maximum compatibility between clients and servers, it is recommended to use PROTOCOL_TLS_CLIENT or PROTOCOL_TLS_SERVER as the protocol version. SSLv2 and SSLv3 are disabled by default.

>>> client_context = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
>>> client_context.options |= ssl.OP_NO_TLSv1
>>> client_context.options |= ssl.OP_NO_TLSv1_1

The SSL context created above will only allow TLSv1.2 and later (if supported by your system) connections to a server. PROTOCOL_TLS_CLIENT implies certificate validation and hostname checks by default. You have to load certificates into the context.

Cipher selection

If you have advanced security requirements, fine-tuning of the ciphers enabled when negotiating a SSL session is possible through the SSLContext.set_ciphers() method. Starting from Python 3.2.3, the ssl module disables certain weak ciphers by default, but you may want to further restrict the cipher choice. Be sure to read OpenSSL's documentation about the cipher list format. If you want to check which ciphers are enabled by a given cipher list, use SSLContext.get_ciphers() or the openssl ciphers command on your system.

Multi-processing

If using this module as part of a multi-processed application (using, for example the multiprocessing or concurrent.futures modules), be aware that OpenSSL's internal random number generator does not properly handle forked processes. Applications must change the PRNG state of the parent process if they use any SSL feature with os.fork(). Any successful call of RAND_add(), RAND_bytes() or RAND_pseudo_bytes() is sufficient.

TLS 1.3

3.7 新版功能.

Python has provisional and experimental support for TLS 1.3 with OpenSSL 1.1.1. The new protocol behaves slightly differently than previous version of TLS/SSL. Some new TLS 1.3 features are not yet available.

• TLS 1.3 uses a disjunct set of cipher suites. All AES-GCM and ChaCha20 cipher suites are enabled by default. The method SSLContext.set_ciphers() cannot enable or disable any TLS 1.3 ciphers yet, but SSLContext.get_ciphers() returns them.

• Session tickets are no longer sent as part of the initial handshake and are handled differently. SSLSocket.session and SSLSession are not compatible with TLS 1.3.

• Client-side certificates are also no longer verified during the initial handshake. A server can request a certificate at any time. Clients process certificate requests while they send or receive application data from the server.

• TLS 1.3 features like early data, deferred TLS client cert request, signature algorithm configuration, and rekeying are not supported yet.

LibreSSL support

LibreSSL is a fork of OpenSSL 1.0.1. The ssl module has limited support for LibreSSL. Some features are not available when the ssl module is compiled with LibreSSL.

• LibreSSL >= 2.6.1 no longer supports NPN. The methods SSLContext.set_npn_protocols() and SSLSocket.selected_npn_protocol() are not available.

• SSLContext.set_default_verify_paths() ignores the env vars SSL_CERT_FILE and SSL_CERT_PATH although get_default_verify_paths() still reports them.

参见

Class socket.socket

Documentation of underlying socket class

SSL/TLS Strong Encryption: An Introduction

Apache HTTP Server文档介绍

RFC 1422: Privacy Enhancement for Internet Electronic Mail: Part II: Certificate-Based Key Management

Steve Kent

RFC 4086: Randomness Requirements for Security

Donald E., Jeffrey I. Schiller

RFC 5280: Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile

D. Cooper

RFC 5246: The Transport Layer Security (TLS) Protocol Version 1.2

T. Dierks et. al.

RFC 6066: Transport Layer Security (TLS) Extensions

D. Eastlake

IANA TLS: Transport Layer Security (TLS) Parameters

IANA

RFC 7525: Recommendations for Secure Use of Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)

IETF

Mozilla's Server Side TLS recommendations

Mozilla