In this code:
def signature(self, value, salt=''):
# Derive a new key from the SECRET_KEY, using the optional salt
key = sha_constructor('signer' + self.key + salt).hexdigest()
return base64_hmac(value, key)
may I suggest putting the salt before the constant string "signer",
like this:
def signature(self, value, salt=''):
# Derive a new key from the SECRET_KEY, using the optional salt
key = sha_constructor(salt + 'signer' + self.key).hexdigest
() ## THIS LINE IS DIFFERENT
return base64_hmac(value, key)
If a constant string comes first, an attacker can calculate the
partial sha hash of 'signer' and cache the state, making this prefix
pretty much useless. By putting the salt first, they'd have to do a
lot more calculation.
There are obviously other corresponding changes when you check the
signature.
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