Issue #1589: Add ssl.match_hostname(), to help implement server identity
verification for higher-level protocols.
diff --git a/Lib/ssl.py b/Lib/ssl.py
index d5e4874..ae8aaef 100644
--- a/Lib/ssl.py
+++ b/Lib/ssl.py
@@ -55,6 +55,7 @@
"""
import textwrap
+import re
import _ssl # if we can't import it, let the error propagate
@@ -85,6 +86,64 @@
import errno
+class CertificateError(ValueError):
+ pass
+
+
+def _dnsname_to_pat(dn):
+ pats = []
+ for frag in dn.split(r'.'):
+ if frag == '*':
+ # When '*' is a fragment by itself, it matches a non-empty dotless
+ # fragment.
+ pats.append('[^.]+')
+ else:
+ # Otherwise, '*' matches any dotless fragment.
+ frag = re.escape(frag)
+ pats.append(frag.replace(r'\*', '[^.]*'))
+ return re.compile(r'\A' + r'\.'.join(pats) + r'\Z', re.IGNORECASE)
+
+
+def match_hostname(cert, hostname):
+ """Verify that *cert* (in decoded format as returned by
+ SSLSocket.getpeercert()) matches the *hostname*. RFC 2818 rules
+ are mostly followed, but IP addresses are not accepted for *hostname*.
+
+ CertificateError is raised on failure. On success, the function
+ returns nothing.
+ """
+ if not cert:
+ raise ValueError("empty or no certificate")
+ dnsnames = []
+ san = cert.get('subjectAltName', ())
+ for key, value in san:
+ if key == 'DNS':
+ if _dnsname_to_pat(value).match(hostname):
+ return
+ dnsnames.append(value)
+ if not san:
+ # The subject is only checked when subjectAltName is empty
+ for sub in cert.get('subject', ()):
+ for key, value in sub:
+ # XXX according to RFC 2818, the most specific Common Name
+ # must be used.
+ if key == 'commonName':
+ if _dnsname_to_pat(value).match(hostname):
+ return
+ dnsnames.append(value)
+ if len(dnsnames) > 1:
+ raise CertificateError("hostname %r "
+ "doesn't match either of %s"
+ % (hostname, ', '.join(map(repr, dnsnames))))
+ elif len(dnsnames) == 1:
+ raise CertificateError("hostname %r "
+ "doesn't match %r"
+ % (hostname, dnsnames[0]))
+ else:
+ raise CertificateError("no appropriate commonName or "
+ "subjectAltName fields were found")
+
+
class SSLContext(_SSLContext):
"""An SSLContext holds various SSL-related configuration options and
data, such as certificates and possibly a private key."""