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Python OpenSSL Manual
__________________________________________________________________
Python OpenSSL Manual
Jean-Paul Calderone
exarkun@twistedmatrix.com
Abstract:
This module is a rather thin wrapper around (a subset of) the OpenSSL
library. With thin wrapper I mean that a lot of the object methods do
nothing more than calling a corresponding function in the OpenSSL
library.
Contents
* 1 Introduction
* 2 Building and Installing
+ 2.1 Building the Module on a Unix System
+ 2.2 Building the Module on a Windows System
* 3 OpenSSL -- Python interface to OpenSSL
+ 3.1 crypto -- Generic cryptographic module
+ 3.2 rand -- An interface to the OpenSSL pseudo random number
generator
+ 3.3 SSL -- An interface to the SSL-specific parts of OpenSSL
* 4 Internals
+ 4.1 Exceptions
+ 4.2 Callbacks
+ 4.3 Acessing Socket Methods
1 Introduction
The reason pyOpenSSL was created is that the SSL support in the socket
module in Python 2.1 (the contemporary version of Python when the
pyOpenSSL project was begun) was severely limited. Other OpenSSL
wrappers for Python at the time were also limited, though in different
ways. Unfortunately, Python's standard library SSL support has remained
weak, although other packages (such as M2Crypto^1) have made great
advances and now equal or exceed pyOpenSSL's functionality.
The reason pyOpenSSL continues to be maintained is that there is a
significant user community around it, as well as a large amount of
software which depends on it. It is a great benefit to many people for
pyOpenSSL to continue to exist and advance.
2 Building and Installing
These instructions can also be found in the file INSTALL.
I have tested this on Debian Linux systems (woody and sid), Solaris 2.6
and 2.7. Others have successfully compiled it on Windows and NT.
2.1 Building the Module on a Unix System
pyOpenSSL uses distutils, so there really shouldn't be any problems. To
build the library:
python setup.py build
If your OpenSSL header files aren't in /usr/include, you may need to
supply the -I flag to let the setup script know where to look. The same
goes for the libraries of course, use the -L flag. Note that build
won't accept these flags, so you have to run first build_ext and then
build! Example:
python setup.py build_ext -I/usr/local/ssl/include -L/usr/local/ssl/lib
python setup.py build
Now you should have a directory called OpenSSL that contains e.g.
SSL.so and __init__.py somewhere in the build dicrectory, so just:
python setup.py install
If you, for some arcane reason, don't want the module to appear in the
site-packages directory, use the --prefix option.
You can, of course, do
python setup.py --help
to find out more about how to use the script.
2.2 Building the Module on a Windows System
Big thanks to Itamar Shtull-Trauring and Oleg Orlov for their help with
Windows build instructions. Same as for Unix systems, we have to
separate the build_ext and the build.
Building the library:
setup.py build_ext -I ...\openssl\inc32 -L ...\openssl\out32dll
setup.py build
Where ...\openssl is of course the location of your OpenSSL
installation.
Installation is the same as for Unix systems:
setup.py install
And similarily, you can do
setup.py --help
to get more information.
3 OpenSSL -- Python interface to OpenSSL
This package provides a high-level interface to the functions in the
OpenSSL library. The following modules are defined:
crypto
Generic cryptographic module. Note that if anything is
incomplete, this module is!
rand
An interface to the OpenSSL pseudo random number generator.
SSL
An interface to the SSL-specific parts of OpenSSL.
3.1 crypto -- Generic cryptographic module
X509Type
See X509.
class X509()
A class representing X.509 certificates.
X509NameType
See X509Name.
class X509Name(x509name)
A class representing X.509 Distinguished Names.
This constructor creates a copy of x509name which should be an
instance of X509Name.
X509ReqType
See X509Req.
class X509Req()
A class representing X.509 certificate requests.
X509StoreType
A Python type object representing the X509Store object type.
PKeyType
See PKey.
class PKey()
A class representing DSA or RSA keys.
PKCS7Type
A Python type object representing the PKCS7 object type.
PKCS12Type
A Python type object representing the PKCS12 object type.
X509ExtensionType
See X509Extension.
class X509Extension(typename, critical, value[, subject][, issuer])
A class representing an X.509 v3 certificate extensions. See
http://openssl.org/docs/apps/x509v3_config.html#STANDARD_EXTENSI
ONSfor typename strings and their options. Optional parameters
subject and issuer must be X509 objects.
NetscapeSPKIType
See NetscapeSPKI.
class NetscapeSPKI([enc])
A class representing Netscape SPKI objects.
If the enc argument is present, it should be a base64-encoded
string representing a NetscapeSPKI object, as returned by the
b64_encode method.
class CRL()
A class representing Certifcate Revocation List objects.
class Revoked()
A class representing Revocation objects of CRL.
FILETYPE_PEM
FILETYPE_ASN1
File type constants.
TYPE_RSA
TYPE_DSA
Key type constants.
exception Error
Generic exception used in the crypto module.
dump_certificate(type, cert)
Dump the certificate cert into a buffer string encoded with the
type type.
dump_certificate_request(type, req)
Dump the certificate request req into a buffer string encoded
with the type type.
dump_privatekey(type, pkey[, cipher, passphrase])
Dump the private key pkey into a buffer string encoded with the
type type, optionally (if type is FILETYPE_PEM) encrypting it
using cipher and passphrase.
passphrase must be either a string or a callback for providing
the pass phrase.
load_certificate(type, buffer)
Load a certificate (X509) from the string buffer encoded with
the type type.
load_certificate_request(type, buffer)
Load a certificate request (X509Req) from the string buffer
encoded with the type type.
load_privatekey(type, buffer[, passphrase])
Load a private key (PKey) from the string buffer encoded with
the type type (must be one of FILETYPE_PEM and FILETYPE_ASN1).
passphrase must be either a string or a callback for providing
the pass phrase.
load_crl(type, buffer)
Load Certificate Revocation List (CRL) data from a string
buffer. buffer encoded with the type type. The type type must
either FILETYPE_PEM or FILETYPE_ASN1).
load_pkcs7_data(type, buffer)
Load pkcs7 data from the string buffer encoded with the type
type.
load_pkcs12(buffer[, passphrase])
Load pkcs12 data from the string buffer. If the pkcs12 structure
is encrypted, a passphrase must be included. The MAC is always
checked and thus required.
See also the man page for the C function PKCS12_parse.
sign(key, data, digest)
Sign a data string using the given key and message digest.
key is a PKey instance. data is a str instance. digest is a str
naming a supported message digest type, for example ``sha1''.
New in version 0.11.
verify(certificate, signature, data, digest)
Verify the signature for a data string.
certificate is a X509 instance corresponding to the private key
which generated the signature. signature is a str instance
giving the signature itself. data is a str instance giving the
data to which the signature applies. digest is a str instance
naming the message digest type of the signature, for example
``sha1''. New in version 0.11.
3.1.1 X509Extension objects
X509Extension objects have the following methods:
get_short_name()
Retrieve the short descriptive name for this extension.
The result is a byte string like ``basicConstraints''. New in
version 0.12.
get_data()
Retrieve the data for this extension.
The result is the ASN.1 encoded form of the extension data as a
byte string. New in version 0.12.
3.1.2 X509 objects
X509 objects have the following methods:
get_issuer()
Return an X509Name object representing the issuer of the
certificate.
get_pubkey()
Return a PKey object representing the public key of the
certificate.
get_serial_number()
Return the certificate serial number.
get_subject()
Return an X509Name object representing the subject of the
certificate.
get_version()
Return the certificate version.
get_notBefore()
Return a string giving the time before which the certificate is
not valid. The string is formatted as an ASN1 GENERALIZEDTIME:
YYYYMMDDhhmmssZ
YYYYMMDDhhmmss+hhmm
YYYYMMDDhhmmss-hhmm
If no value exists for this field, None is returned.
get_notAfter()
Return a string giving the time after which the certificate is
not valid. The string is formatted as an ASN1 GENERALIZEDTIME:
YYYYMMDDhhmmssZ
YYYYMMDDhhmmss+hhmm
YYYYMMDDhhmmss-hhmm
If no value exists for this field, None is returned.
set_notBefore(when)
Change the time before which the certificate is not valid. when
is a string formatted as an ASN1 GENERALIZEDTIME:
YYYYMMDDhhmmssZ
YYYYMMDDhhmmss+hhmm
YYYYMMDDhhmmss-hhmm
set_notAfter(when)
Change the time after which the certificate is not valid. when
is a string formatted as an ASN1 GENERALIZEDTIME:
YYYYMMDDhhmmssZ
YYYYMMDDhhmmss+hhmm
YYYYMMDDhhmmss-hhmm
gmtime_adj_notBefore(time)
Adjust the timestamp (in GMT) when the certificate starts being
valid.
gmtime_adj_notAfter(time)
Adjust the timestamp (in GMT) when the certificate stops being
valid.
has_expired()
Checks the certificate's time stamp against current time.
Returns true if the certificate has expired and false otherwise.
set_issuer(issuer)
Set the issuer of the certificate to issuer.
set_pubkey(pkey)
Set the public key of the certificate to pkey.
set_serial_number(serialno)
Set the serial number of the certificate to serialno.
set_subject(subject)
Set the subject of the certificate to subject.
set_version(version)
Set the certificate version to version.
sign(pkey, digest)
Sign the certificate, using the key pkey and the message digest
algorithm identified by the string digest.
subject_name_hash()
Return the hash of the certificate subject.
digest(digest_name)
Return a digest of the certificate, using the digest_name
method. digest_name must be a string describing a digest
algorithm supported by OpenSSL (by EVP_get_digestbyname,
specifically). For example, "md5" or "sha1".
add_extensions(extensions)
Add the extensions in the sequence extensions to the
certificate.
get_extension_count()
Return the number of extensions on this certificate. New in
version 0.12.
get_extension(index)
Retrieve the extension on this certificate at the given index.
Extensions on a certificate are kept in order. The index
parameter selects which extension will be returned. The returned
object will be an X509Extension instance. New in version 0.12.
3.1.3 X509Name objects
X509Name objects have the following methods:
hash()
Return an integer giving the first four bytes of the MD5 digest
of the DER representation of the name.
der()
Return a string giving the DER representation of the name.
get_components()
Return a list of two-tuples of strings giving the components of
the name.
X509Name objects have the following members:
countryName
The country of the entity. C may be used as an alias for
countryName.
stateOrProvinceName
The state or province of the entity. ST may be used as an alias
for stateOrProvinceName·
localityName
The locality of the entity. L may be used as an alias for
localityName.
organizationName
The organization name of the entity. O may be used as an alias
for organizationName.
organizationalUnitName
The organizational unit of the entity. OU may be used as an
alias for organizationalUnitName.
commonName
The common name of the entity. CN may be used as an alias for
commonName.
emailAddress
The e-mail address of the entity.
3.1.4 X509Req objects
X509Req objects have the following methods:
get_pubkey()
Return a PKey object representing the public key of the
certificate request.
get_subject()
Return an X509Name object representing the subject of the
certificate.
set_pubkey(pkey)
Set the public key of the certificate request to pkey.
sign(pkey, digest)
Sign the certificate request, using the key pkey and the message
digest algorithm identified by the string digest.
verify(pkey)
Verify a certificate request using the public key pkey.
set_version(version)
Set the version (RFC 2459, 4.1.2.1) of the certificate request
to version.
get_version()
Get the version (RFC 2459, 4.1.2.1) of the certificate request.
3.1.5 X509Store objects
The X509Store object has currently just one method:
add_cert(cert)
Add the certificate cert to the certificate store.
3.1.6 PKey objects
The PKey object has the following methods:
bits()
Return the number of bits of the key.
generate_key(type, bits)
Generate a public/private key pair of the type type (one of
TYPE_RSA and TYPE_DSA) with the size bits.
type()
Return the type of the key.
3.1.7 PKCS7 objects
PKCS7 objects have the following methods:
type_is_signed()
FIXME
type_is_enveloped()
FIXME
type_is_signedAndEnveloped()
FIXME
type_is_data()
FIXME
get_type_name()
Get the type name of the PKCS7.
3.1.8 PKCS12 objects
PKCS12 objects have the following methods:
export([passphrase=None][, iter=2048][, maciter=1])
Returns a PKCS12 object as a string.
The optional passphrase must be a string not a callback.
See also the man page for the C function PKCS12_create.
get_ca_certificates()
Return CA certificates within the PKCS12 object as a tuple.
Returns None if no CA certificates are present.
get_certificate()
Return certificate portion of the PKCS12 structure.
get_friendlyname()
Return friendlyName portion of the PKCS12 structure.
get_privatekey()
Return private key portion of the PKCS12 structure
set_ca_certificates(cacerts)
Replace or set the CA certificates within the PKCS12 object with
the sequence cacerts.
Set cacerts to None to remove all CA certificates.
set_certificate(cert)
Replace or set the certificate portion of the PKCS12 structure.
set_friendlyname(name)
Replace or set the friendlyName portion of the PKCS12 structure.
set_privatekey(pkey)
Replace or set private key portion of the PKCS12 structure
3.1.9 X509Extension objects
X509Extension objects have several methods:
get_critical()
Return the critical field of the extension object.
get_short_name()
Return the short type name of the extension object.
3.1.10 NetscapeSPKI objects
NetscapeSPKI objects have the following methods:
b64_encode()
Return a base64-encoded string representation of the object.
get_pubkey()
Return the public key of object.
set_pubkey(key)
Set the public key of the object to key.
sign(key, digest_name)
Sign the NetscapeSPKI object using the given key and
digest_name. digest_name must be a string describing a digest
algorithm supported by OpenSSL (by EVP_get_digestbyname,
specifically). For example, "md5" or "sha1".
verify(key)
Verify the NetscapeSPKI object using the given key.
3.1.11 CRL objects
CRL objects have the following methods:
add_revoked(revoked)
Add a Revoked object to the CRL, by value not reference.
export(cert, key[, type=FILETYPE_PEM][, days=100])
Use cert and key to sign the CRL and return the CRL as a string.
days is the number of days before the next CRL is due.
get_revoked()
Return a tuple of Revoked objects, by value not reference.
3.1.12 Revoked objects
Revoked objects have the following methods:
all_reasons()
Return a list of all supported reasons.
get_reason()
Return the revocation reason as a str. Can be None, which
differs from "Unspecified".
get_rev_date()
Return the revocation date as a str. The string is formatted as
an ASN1 GENERALIZEDTIME.
get_serial()
Return a str containing a hex number of the serial of the
revoked certificate.
set_reason(reason)
Set the revocation reason. reason must be None or a string, but
the values are limited. Spaces and case are ignored. See
all_reasons.
set_rev_date(date)
Set the revocation date. The string is formatted as an ASN1
GENERALIZEDTIME.
set_serial(serial)
serial is a string containing a hex number of the serial of the
revoked certificate.
3.2 rand -- An interface to the OpenSSL pseudo random number generator
This module handles the OpenSSL pseudo random number generator (PRNG)
and declares the following:
add(string, entropy)
Mix bytes from string into the PRNG state. The entropy argument
is (the lower bound of) an estimate of how much randomness is
contained in string, measured in bytes. For more information,
see e.g. RFC 1750.
bytes(num_bytes)
Get some random bytes from the PRNG as a string.
This is a wrapper for the C function RAND_bytes.
cleanup()
Erase the memory used by the PRNG.
This is a wrapper for the C function RAND_cleanup.
egd(path[, bytes])
Query the Entropy Gathering Daemon^2 on socket path for bytes
bytes of random data and and uses add to seed the PRNG. The
default value of bytes is 255.
load_file(path[, bytes])
Read bytes bytes (or all of it, if bytes is negative) of data
from the file path to seed the PRNG. The default value of bytes
is -1.
screen()
Add the current contents of the screen to the PRNG state.
Availability: Windows.
seed(string)
This is equivalent to calling add with entropy as the length of
the string.
status()
Returns true if the PRNG has been seeded with enough data, and
false otherwise.
write_file(path)
Write a number of random bytes (currently 1024) to the file
path. This file can then be used with load_file to seed the PRNG
again.
exception Error
If the current RAND method supports any errors, this is raised
when needed. The default method does not raise this when the
entropy pool is depleted.
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.
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.
ContextType
See Context.
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.
ConnectionType
See Connection.
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).
3.3.1 Context objects
Context objects have the following methods:
check_privatekey()
Check if the private key (loaded with use_privatekey[_file])
matches the certificate (loaded with use_certificate[_file]).
Returns None if they match, raises Error otherwise.
get_app_data()
Retrieve application data as set by set_app_data.
get_cert_store()
Retrieve the certificate store (a X509Store object) that the
context uses. This can be used to add "trusted" certificates
without using the. load_verify_locations() method.
get_timeout()
Retrieve session timeout, as set by set_timeout. The default is
300 seconds.
get_verify_depth()
Retrieve the Context object's verify depth, as set by
set_verify_depth.
get_verify_mode()
Retrieve the Context object's verify mode, as set by set_verify.
load_client_ca(pemfile)
Read a file with PEM-formatted certificates that will be sent to
the client when requesting a client certificate.
set_client_ca_list(certificate_authorities)
Replace the current list of preferred certificate signers that
would be sent to the client when requesting a client certificate
with the certificate_authorities sequence of
OpenSSL.crypto.X509Names.
New in version 0.10.
add_client_ca(certificate_authority)
Extract a OpenSSL.crypto.X509Name from the certificate_authority
OpenSSL.crypto.X509 certificate and add it to the list of
preferred certificate signers sent to the client when requesting
a client certificate.
New in version 0.10.
load_verify_locations(pemfile, capath)
Specify where CA certificates for verification purposes are
located. These are trusted certificates. Note that the
certificates have to be in PEM format. If capath is passed, it
must be a directory prepared using the c_rehash tool included
with OpenSSL. Either, but not both, of pemfile or capath may be
None.
set_default_verify_paths()
Specify that the platform provided CA certificates are to be
used for verification purposes. This method may not work
properly on OS X.
load_tmp_dh(dhfile)
Load parameters for Ephemeral Diffie-Hellman from dhfile.
set_app_data(data)
Associate data with this Context object. data can be retrieved
later using the get_app_data method.
set_cipher_list(ciphers)
Set the list of ciphers to be used in this context. See the
OpenSSL manual for more information (e.g. ciphers(1))
set_info_callback(callback)
Set the information callback to callback. This function will be
called from time to time during SSL handshakes. callback should
take three arguments: a Connection object and two integers. The
first integer specifies where in the SSL handshake the function
was called, and the other the return code from a (possibly
failed) internal function call.
set_options(options)
Add SSL options. Options you have set before are not cleared!
This method should be used with the OP_* constants.
set_passwd_cb(callback[, userdata])
Set the passphrase callback to callback. This function will be
called when a private key with a passphrase is loaded. callback
must accept three positional arguments. First, an integer giving
the maximum length of the passphrase it may return. If the
returned passphrase is longer than this, it will be truncated.
Second, a boolean value which will be true if the user should be
prompted for the passphrase twice and the callback should verify
that the two values supplied are equal. Third, the value given
as the userdata parameter to set_passwd_cb. If an error occurs,
callback should return a false value (e.g. an empty string).
set_session_id(name)
Set the context name within which a session can be reused for
this Context object. This is needed when doing session
resumption, because there is no way for a stored session to know
which Context object it is associated with. name may be any
binary data.
set_timeout(timeout)
Set the timeout for newly created sessions for this Context
object to timeout. timeout must be given in (whole) seconds. The
default value is 300 seconds. See the OpenSSL manual for more
information (e.g. SSL_CTX_set_timeout(3)).
set_verify(mode, callback)
Set the verification flags for this Context object to mode and
specify that callback should be used for verification callbacks.
mode should be one of VERIFY_NONE and VERIFY_PEER. If
VERIFY_PEER is used, mode can be OR:ed with
VERIFY_FAIL_IF_NO_PEER_CERT and VERIFY_CLIENT_ONCE to further
control the behaviour. callback should take five arguments: A
Connection object, an X509 object, and three integer variables,
which are in turn potential error number, error depth and return
code. callback should return true if verification passes and
false otherwise.
set_verify_depth(depth)
Set the maximum depth for the certificate chain verification
that shall be allowed for this Context object.
use_certificate(cert)
Use the certificate cert which has to be a X509 object.
add_extra_chain_cert(cert)
Adds the certificate cert, which has to be a X509 object, to the
certificate chain presented together with the certificate.
use_certificate_chain_file(file)
Load a certificate chain from file which must be PEM encoded.
use_privatekey(pkey)
Use the private key pkey which has to be a PKey object.
use_certificate_file(file[, format])
Load the first certificate found in file. The certificate must
be in the format specified by format, which is either
FILETYPE_PEM or FILETYPE_ASN1. The default is FILETYPE_PEM.
use_privatekey_file(file[, format])
Load the first private key found in file. The private key must
be in the format specified by format, which is either
FILETYPE_PEM or FILETYPE_ASN1. The default is FILETYPE_PEM.
3.3.2 Connection objects
Connection objects have the following methods:
accept()
Call the accept method of the underlying socket and set up SSL
on the returned socket, using the Context object supplied to
this Connection object at creation. Returns a pair (conn,
address). where conn is the new Connection object created, and
address is as returned by the socket's accept.
bind(address)
Call the bind method of the underlying socket.
close()
Call the close method of the underlying socket. Note: If you
want correct SSL closure, you need to call the shutdown method
first.
connect(address)
Call the connect method of the underlying socket and set up SSL
on the socket, using the Context object supplied to this
Connection object at creation.
connect_ex(address)
Call the connect_ex method of the underlying socket and set up
SSL on the socket, using the Context object supplied to this
Connection object at creation. Note that if the connect_ex
method of the socket doesn't return 0, SSL won't be initialized.
do_handshake()
Perform an SSL handshake (usually called after renegotiate or
one of set_accept_state or set_accept_state). This can raise the
same exceptions as send and recv.
fileno()
Retrieve the file descriptor number for the underlying socket.
listen(backlog)
Call the listen method of the underlying socket.
get_app_data()
Retrieve application data as set by set_app_data.
get_cipher_list()
Retrieve the list of ciphers used by the Connection object.
WARNING: This API has changed. It used to take an optional
parameter and just return a string, but not it returns the
entire list in one go.
get_client_ca_list()
Retrieve the list of preferred client certificate issuers sent
by the server as OpenSSL.crypto.X509Name objects.
If this is a client Connection, the list will be empty until the
connection with the server is established.
If this is a server Connection, return the list of certificate
authorities that will be sent or has been sent to the client, as
controlled by this Connection's Context.
New in version 0.10.
get_context()
Retrieve the Context object associated with this Connection.
get_peer_certificate()
Retrieve the other side's certificate (if any)
getpeername()
Call the getpeername method of the underlying socket.
getsockname()
Call the getsockname method of the underlying socket.
getsockopt(level, optname[, buflen])
Call the getsockopt method of the underlying socket.
pending()
Retrieve the number of bytes that can be safely read from the
SSL buffer (not the underlying transport buffer).
recv(bufsize)
Receive data from the Connection. The return value is a string
representing the data received. The maximum amount of data to be
received at once, is specified by bufsize.
bio_write(bytes)
If the Connection was created with a memory BIO, this method can
be used to add bytes to the read end of that memory BIO. The
Connection can then read the bytes (for example, in response to
a call to recv).
renegotiate()
Renegotiate the SSL session. Call this if you wish to change
cipher suites or anything like that.
send(string)
Send the string data to the Connection.
bio_read(bufsize)
If the Connection was created with a memory BIO, this method can
be used to read bytes from the write end of that memory BIO.
Many Connection methods will add bytes which must be read in
this manner or the buffer will eventually fill up and the
Connection will be able to take no further actions.
sendall(string)
Send all of the string data to the Connection. This calls send
repeatedly until all data is sent. If an error occurs, it's
impossible to tell how much data has been sent.
set_accept_state()
Set the connection to work in server mode. The handshake will be
handled automatically by read/write.
set_app_data(data)
Associate data with this Connection object. data can be
retrieved later using the get_app_data method.
set_connect_state()
Set the connection to work in client mode. The handshake will be
handled automatically by read/write.
setblocking(flag)
Call the setblocking method of the underlying socket.
setsockopt(level, optname, value)
Call the setsockopt method of the underlying socket.
shutdown()
Send the shutdown message to the Connection. Returns true if the
shutdown message exchange is completed and false otherwise (in
which case you call recv() or send() when the connection becomes
readable/writeable.
get_shutdown()
Get the shutdown state of the Connection. Returns a bitvector of
either or both of SENT_SHUTDOWN and RECEIVED_SHUTDOWN.
set_shutdown(state)
Set the shutdown state of the Connection. state is a bitvector
of either or both of SENT_SHUTDOWN and RECEIVED_SHUTDOWN.
sock_shutdown(how)
Call the shutdown method of the underlying socket.
bio_shutdown()
If the Connection was created with a memory BIO, this method can
be used to indicate that ``end of file'' has been reached on the
read end of that memory BIO.
state_string()
Retrieve a verbose string detailing the state of the Connection.
client_random()
Retrieve the random value used with the client hello message.
server_random()
Retrieve the random value used with the server hello message.
master_key()
Retrieve the value of the master key for this session.
want_read()
Checks if more data has to be read from the transport layer to
complete an operation.
want_write()
Checks if there is data to write to the transport layer to
complete an operation.
4 Internals
We ran into three main problems developing this: Exceptions, callbacks
and accessing socket methods. This is what this chapter is about.
4.1 Exceptions
We realized early that most of the exceptions would be raised by the
I/O functions of OpenSSL, so it felt natural to mimic OpenSSL's error
code system, translating them into Python exceptions. This naturally
gives us the exceptions SSL.ZeroReturnError, SSL.WantReadError,
SSL.WantWriteError, SSL.WantX509LookupError and SSL.SysCallError.
For more information about this, see section 3.3.
4.2 Callbacks
There are a number of problems with callbacks. First of all, OpenSSL is
written as a C library, it's not meant to have Python callbacks, so a
way around that is needed. Another problem is thread support. A lot of
the OpenSSL I/O functions can block if the socket is in blocking mode,
and then you want other Python threads to be able to do other things.
The real trouble is if you've released the global CPython interpreter
lock to do a potentially blocking operation, and the operation calls a
callback. Then we must take the GIL back, since calling Python APIs
without holding it is not allowed.
There are two solutions to the first problem, both of which are
necessary. The first solution to use is if the C callback allows
''userdata'' to be passed to it (an arbitrary pointer normally). This
is great! We can set our Python function object as the real userdata
and emulate userdata for the Python function in another way. The other
solution can be used if an object with an ''app_data'' system always is
passed to the callback. For example, the SSL object in OpenSSL has
app_data functions and in e.g. the verification callbacks, you can
retrieve the related SSL object. What we do is to set our wrapper
Connection object as app_data for the SSL object, and we can easily
find the Python callback.
The other problem is solved using thread local variables. Whenever the
GIL is released before calling into an OpenSSL API, the PyThreadState
pointer returned by PyEval_SaveState is stored in a global thread local
variable (using Python's own TLS API, PyThread_set_key_value). When it
is necessary to re-acquire the GIL, either after the OpenSSL API
returns or in a C callback invoked by that OpenSSL API, the value of
the thread local variable is retrieved (PyThread_get_key_value) and
used to re-acquire the GIL. This allows Python threads to execute while
OpenSSL APIs are running and allows use of any particular pyOpenSSL
object from any Python thread, since there is no per-thread state
associated with any of these objects and since OpenSSL is threadsafe
(as long as properly initialized, as pyOpenSSL initializes it).
4.3 Acessing Socket Methods
We quickly saw the benefit of wrapping socket methods in the
SSL.Connection class, for an easy transition into using SSL. The
problem here is that the socket module lacks a C API, and all the
methods are declared static. One approach would be to have OpenSSL as a
submodule to the socket module, placing all the code in socketmodule.c,
but this is obviously not a good solution, since you might not want to
import tonnes of extra stuff you're not going to use when importing the
socket module. The other approach is to somehow get a pointer to the
method to be called, either the C function, or a callable Python
object. This is not really a good solution either, since there's a lot
of lookups involved.
The way it works is that you have to supply a ``socket-like'' transport
object to the SSL.Connection. The only requirement of this object is
that it has a fileno() method that returns a file descriptor that's
valid at the C level (i.e. you can use the system calls read and
write). If you want to use the connect() or accept() methods of the
SSL.Connection object, the transport object has to supply such methods
too. Apart from them, any method lookups in the SSL.Connection object
that fail are passed on to the underlying transport object.
Future changes might be to allow Python-level transport objects, that
instead of having fileno() methods, have read() and write() methods, so
more advanced features of Python can be used. This would probably
entail some sort of OpenSSL ``BIOs'', but converting Python strings
back and forth is expensive, so this shouldn't be used unless
necessary. Other nice things would be to be able to pass in different
transport objects for reading and writing, but then the fileno() method
of SSL.Connection becomes virtually useless. Also, should the method
resolution be used on the read-transport or the write-transport?
About this document ...
Python OpenSSL Manual
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Footnotes
... M2Crypto^1
See http://chandlerproject.org/Projects/MeTooCrypto
... Daemon^2
See http://www.lothar.com/tech/crypto/
... 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!
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Python OpenSSL Manual
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Release 0.12.