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Add support for server hostname verification #796

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Add support for server hostname verification #796

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b330cc3
Add support for server hostname verification
kaie Oct 9, 2018
fa858c0
Protect new code with Cryptography_HAS_102_VERIFICATION_PARAMS
kaie Oct 10, 2018
dd473fb
Use SAN only hostname verification, don't fall back to subject. Use f…
kaie Oct 10, 2018
872ab00
drop unnecessary semicolons
kaie Oct 10, 2018
37be205
fix whitespace
kaie Oct 11, 2018
5711348
avoid lines >= 80 chars
kaie Oct 11, 2018
ff6db2c
Fix hanging indent
kaie Oct 11, 2018
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17 changes: 17 additions & 0 deletions src/OpenSSL/SSL.py
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Original file line number Diff line number Diff line change
Expand Up @@ -665,6 +665,12 @@ def explode(*args, **kwargs):
)


_requires_x509_verify = _make_requires(
_lib.Cryptography_HAS_102_VERIFICATION_PARAMS,
"X509 verification not available"
)


class Session(object):
"""
A class representing an SSL session. A session defines certain connection
Expand Down Expand Up @@ -1688,6 +1694,17 @@ def set_tlsext_host_name(self, name):
# XXX I guess this can fail sometimes?
_lib.SSL_set_tlsext_host_name(self._ssl, name)

@_requires_x509_verify
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What do you think about integrating this into set_tlsext_host_name, so there's only a single method call required for correct/secure usage?

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Certainly doable, but the main difference with set_tlsext_host_name is that it should not be called on IP addresses, per RFC6066, Section 3

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Excellent point, you have to use X509_VERIFY_PARAM_set1_ip() for IP address validation any way. Feel free to copy my implementation from Python's ssl module. The function _ssl_configure_hostname() takes care of SNI, hostname verification, and special cases IP addresses.

https://github.com/python/cpython/blob/ba251c2ae6654bfc8abd9d886b219698ad34ac3c/Modules/_ssl.c#L862-L926

def set_verify_host_name(self, hostname):
param = _lib.SSL_get0_param(self._ssl)
flags = _lib.X509_CHECK_FLAG_NO_PARTIAL_WILDCARDS
if _lib.Cryptography_HAS_110_VERIFICATION_PARAMS:
flags |= _lib.X509_CHECK_FLAG_NEVER_CHECK_SUBJECT
_lib.X509_VERIFY_PARAM_set_hostflags(param, flags)
if not _lib.X509_VERIFY_PARAM_set1_host(param, hostname,
len(hostname)):
raise Error("X509_VERIFY_PARAM_set1_host call failed")

def pending(self):
"""
Get the number of bytes that can be safely read from the SSL buffer
Expand Down