DH docs should do a better job telling people to use a KDF

pyca / cryptography

cryptography is a package designed to expose cryptographic primitives and recipes to Python developers.

https://cryptography.io

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DH docs should do a better job telling people to use a KDF #4005

Closed alex closed 6 years ago

alex commented 7 years ago

https://cryptography.io/en/latest/hazmat/primitives/asymmetric/x25519/#exchange-algorithm (and the same in the ECDH and FFDH docs)

We should a) include a KDF in the example, b) use more words to describe wtf we're saying about kdfs and better motivate the why

jlaine commented 6 years ago

This is a little arcane for a "good first issue"!

From my reading so far, this is what I've come up with :

For most applications the shared_key should be passed to a key derivation function
in order to produce a key with the expected number of random bits, and to destroy
mathematical structure in the shared_key which might be used by an attacker.