Am Mittwoch, 9. Januar 2019, 00:54:22 CET schrieb Andy Lutomirski: Hi Andy, > > I think that, if the crypto API is going to grow a KDF facility, it should > be done right. Have a key type or flag or whatever that says “this key may > *only* be used to derive keys using such-and-such algorithm”, and have a > helper to derive a key. That helper should take some useful parameters and > mix them in: > > - What type of key is being derived? ECDSA signing key? HMAC key? AES > key? > > - Can user code access the derived key? > > - What is the key’s purpose? “Encrypt and authenticate a hibernation image” > would be a purpose. > > - Number of bytes. > > All of these parameters should be mixed in to the key derivation. > > Also, an AE key, even for AES+HMAC, should be just one derived key. If you > need 512 bits, ask for a 512-bit key, not two 256-bit keys.
I concur with your requirements. However, is the kernel crypto API the right place to enforce such policies? To me, the kernel crypto API is a tinker-toy set of ciphers. The real policy enforcer would or should be the keyring facility. Thus, may I propose to: - implement the cryptographic primitive of the KDF in the kernel crypto API - implement the policy system how to use the KDF in the keyring facility Ciao Stephan
