7
votes
2answers
355 views

Is it secure to derive an AES key from a MAC?

I'm working on a project where we need to encrypt a large number of files and store them on the cloud. And I'm wondering if the following process would be secure (we have a “Hardware Security Module” ...
3
votes
2answers
90 views

Combining two keys

What is the most secure way to combine two "random" keys X of size k (k ≤ 512 bits) and Y of size 512 bits in one key Z of size k? Result Z will be used for encryption/decryption with various ...
4
votes
1answer
86 views

Key Derivation from random salted seed, HMAC and HMAC based KDF

I would like to generate a key which would be good enough to be used for encryption with AES in a mobile environment. My idea is to use as a seed ''random attributes'' from a mobile device. Is hashing ...
2
votes
3answers
116 views

Encrypt-then-MAC: full random keys or keys derived from master key?

I have this scenario where I use Encrypt-then-MAC (AES256-CBC and HMAC-SHA256) with keys generated by a CSPRNG (specifically, SecureRandom in Java). I'd like to know which is better: Use the CSPRNG ...
2
votes
1answer
65 views

Why would splitting a password output be better than separate HMACs for encryption/authentication key derivation?

In a recent question I asked here on crypto.se, an answer was given that surprised me a bit. As mentioned in the referenced question, I'm looking to derive encryption and authentication keys from ...
0
votes
1answer
162 views

Encryption and HMAC key derivation

I'm deriving keys from a user-supplied passphrase for symmetric encryption using AES-256 in CBC mode with a HMAC for authenticity/integrity. My key derivation function currently looks like this: ...
6
votes
2answers
364 views

Which risks are associated with deriving multiple keys from the same DH secret Z?

NIST recommends Krawczyk's HMAC-based key derivation function (HKDF) in SP-800-56C (PDF). HKDF shall e.g. be used to create keys from shared secrets after Diffie Hellman key establishment. NIST ...
2
votes
1answer
284 views

What are the safe ways to derive HMAC key using block cipher?

Suppose we have a state of block cipher initialized with some key unknown to us, that is, we have the state after running key schedule, but we have no access to actual key or subkeys, all we can do is ...