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Issue #20995: Enhance default ciphers used by the ssl module

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Closes #20995 by Enabling better security by prioritizing ciphers
such that:

* Prefer cipher suites that offer perfect forward secrecy (DHE/ECDHE)
* Prefer ECDHE over DHE for better performance
* Prefer any AES-GCM over any AES-CBC for better performance and security
* Then Use HIGH cipher suites as a fallback
* Then Use 3DES as fallback which is secure but slow
* Finally use RC4 as a fallback which is problematic but needed for
  compatibility some times.
* Disable NULL authentication, NULL encryption, and MD5 MACs for security
  reasons
This commit is contained in:
Donald Stufft 2014-03-21 21:33:34 -04:00
parent 51f3129ba2
commit 79ccaa2cad
3 changed files with 37 additions and 18 deletions
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37
Lib/ssl.py
View file

@ -162,14 +162,37 @@ else:
# Disable weak or insecure ciphers by default
# (OpenSSL's default setting is 'DEFAULT:!aNULL:!eNULL')
_DEFAULT_CIPHERS = 'DEFAULT:!aNULL:!eNULL:!LOW:!EXPORT:!SSLv2'
# Enable a better set of ciphers by default
# This list has been explicitly chosen to:
# * Prefer cipher suites that offer perfect forward secrecy (DHE/ECDHE)
# * Prefer ECDHE over DHE for better performance
# * Prefer any AES-GCM over any AES-CBC for better performance and security
# * Then Use HIGH cipher suites as a fallback
# * Then Use 3DES as fallback which is secure but slow
# * Finally use RC4 as a fallback which is problematic but needed for
# compatibility some times.
# * Disable NULL authentication, NULL encryption, and MD5 MACs for security
# reasons
_DEFAULT_CIPHERS = (
'ECDH+AESGCM:DH+AESGCM:ECDH+AES256:DH+AES256:ECDH+AES128:DH+AES:ECDH+HIGH:'
'DH+HIGH:ECDH+3DES:DH+3DES:RSA+AESGCM:RSA+AES:RSA+HIGH:RSA+3DES:ECDH+RC4:'
'DH+RC4:RSA+RC4:!aNULL:!eNULL:!MD5'
)
# restricted and more secure ciphers
# HIGH: high encryption cipher suites with key length >= 128 bits (no MD5)
# !aNULL: only authenticated cipher suites (no anonymous DH)
# !RC4: no RC4 streaming cipher, RC4 is broken
# !DSS: RSA is preferred over DSA
_RESTRICTED_CIPHERS = 'HIGH:!aNULL:!RC4:!DSS'
# Restricted and more secure ciphers
# This list has been explicitly chosen to:
# * Prefer cipher suites that offer perfect forward secrecy (DHE/ECDHE)
# * Prefer ECDHE over DHE for better performance
# * Prefer any AES-GCM over any AES-CBC for better performance and security
# * Then Use HIGH cipher suites as a fallback
# * Then Use 3DES as fallback which is secure but slow
# * Disable NULL authentication, NULL encryption, MD5 MACs, DSS, and RC4 for
# security reasons
_RESTRICTED_CIPHERS = (
'ECDH+AESGCM:DH+AESGCM:ECDH+AES256:DH+AES256:ECDH+AES128:DH+AES:ECDH+HIGH:'
'DH+HIGH:ECDH+3DES:DH+3DES:RSA+AESGCM:RSA+AES:RSA+HIGH:RSA+3DES:!aNULL:'
'!eNULL:!MD5:!DSS:!RC4'
)
class CertificateError(ValueError):