target = "https://tools.ietf.org/rfc/rfc7627#section-6.2"

# 6.2.  Cryptographic Properties of the Hash Function
#
# The session hashes of two different sessions need to be distinct;
# hence, the "Hash" function used to compute the "session_hash" needs
# to be collision resistant.  As such, hash functions such as MD5 or
# SHA1 are NOT RECOMMENDED.
# 
# We observe that the "Hash" function used in the Finished message
# computation already needs to be collision resistant for the
# renegotiation indication extension [RFC5746] to work, because a
# meaningful collision on the handshake messages (and hence on the
# "verify_data") may re-enable the renegotiation attack [Ray09].
# 
# The hash function used to compute the session hash depends on the TLS
# protocol version.  All current ciphersuites defined for TLS 1.2 use
# SHA256 or better, and so does the session hash.  For earlier versions
# of the protocol, only MD5 and SHA1 can be assumed to be supported,
# and this document does not require legacy implementations to add
# support for new hash functions.  In these versions, the session hash
# uses the concatenation of MD5 and SHA1, as in the Finished message.

[[spec]]
level = "SHOULD"
quote = '''
As such, hash functions such as MD5 or
SHA1 are NOT RECOMMENDED.
'''

