3.1.1 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_signature_algorithm()
- 
Return the signature algorithm used in the certificate.  If the algorithm is
undefined, raise ValueError.
- 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,Noneis 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,Noneis 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.