3.3 SSL -- An interface to the SSL-specific parts of OpenSSL

3.3 `SSL` -- An interface to the SSL-specific parts of OpenSSL

This module handles things specific to SSL. There are two objects defined: Context, Connection.

SSLv2_METHOD
SSLv3_METHOD
SSLv23_METHOD
TLSv1_METHOD: These constants represent the different SSL methods to use when creating a context object.

VERIFY_NONE
VERIFY_PEER
VERIFY_FAIL_IF_NO_PEER_CERT: These constants represent the verification mode used by the Context object's set_verify method.

FILETYPE_PEM
FILETYPE_ASN1: File type constants used with the use_certificate_file and use_privatekey_file methods of Context objects.

OP_SINGLE_DH_USE
OP_EPHEMERAL_RSA
OP_NO_SSLv2
OP_NO_SSLv3
OP_NO_TLSv1: Constants used with set_options of Context objects. OP_SINGLE_DH_USE means to always create a new key when using ephemeral Diffie-Hellman. OP_EPHEMERAL_RSA means to always use ephemeral RSA keys when doing RSA operations. OP_NO_SSLv2, OP_NO_SSLv3 and OP_NO_TLSv1 means to disable those specific protocols. This is interesting if you're using e.g. SSLv23_METHOD to get an SSLv2-compatible handshake, but don't want to use SSLv2.

SSLEAY_VERSION
SSLEAY_CFLAGS
SSLEAY_BUILT_ON
SSLEAY_PLATFORM
SSLEAY_DIR: Constants used with SSLeay_version to specify what OpenSSL version information to retrieve. See the man page for the SSLeay_version C API for details.

OPENSSL_VERSION_NUMBER: An integer giving the version number of the OpenSSL library used to build this version of pyOpenSSL. See the man page for the SSLeay_version C API for details.

SSLeay_version(type): Retrieve a string describing some aspect of the underlying OpenSSL version. The type passed in should be one of the SSLEAY_* constants defined in this module.

class Context(method): A class representing SSL contexts. Contexts define the parameters of one or more SSL connections.
method should be SSLv2_METHOD, SSLv3_METHOD, SSLv23_METHOD or TLSv1_METHOD.

class Connection(context, socket): A class representing SSL connections.
context should be an instance of Context and socket should be a socket ³ object. socket may be None; in this case, the Connection is created with a memory BIO: see the bio_read, bio_write, and bio_shutdown methods.

exception Error: This exception is used as a base class for the other SSL-related exceptions, but may also be raised directly.
Whenever this exception is raised directly, it has a list of error messages from the OpenSSL error queue, where each item is a tuple (lib, function, reason). Here lib, function and reason are all strings, describing where and what the problem is. See err(3) for more information.

exception ZeroReturnError: This exception matches the error return code SSL_ERROR_ZERO_RETURN, and is raised when the SSL Connection has been closed. In SSL 3.0 and TLS 1.0, this only occurs if a closure alert has occurred in the protocol, i.e. the connection has been closed cleanly. Note that this does not necessarily mean that the transport layer (e.g. a socket) has been closed.
It may seem a little strange that this is an exception, but it does match an SSL_ERROR code, and is very convenient.

exception WantReadError: The operation did not complete; the same I/O method should be called again later, with the same arguments. Any I/O method can lead to this since new handshakes can occur at any time.
The wanted read is for dirty data sent over the network, not the clean data inside the tunnel. For a socket based SSL connection, read means data coming at us over the network. Until that read succeeds, the attempted OpenSSL.SSL.Connection.recv, OpenSSL.SSL.Connection.send, or OpenSSL.SSL.Connection.do_handshake is prevented or incomplete. You probably want to select() on the socket before trying again.

exception WantWriteError: See WantReadError. The socket send buffer may be too full to write more data.

exception WantX509LookupError: The operation did not complete because an application callback has asked to be called again. The I/O method should be called again later, with the same arguments. Note: This won't occur in this version, as there are no such callbacks in this version.

exception SysCallError: The SysCallError occurs when there's an I/O error and OpenSSL's error queue does not contain any information. This can mean two things: An error in the transport protocol, or an end of file that violates the protocol. The parameter to the exception is always a pair (errnum, errstr).

... socket ³: Actually, all that is required is an object that behaves like a socket, you could even use files, even though it'd be tricky to get the handshakes right!