read
RFC 5869 HMAC-based Extract-and-Expand Key Derivation Function (HKDF). H.
Krawczyk, P. Eronen. May 2010. (Format: TXT, HTML) (Status:
INFORMATIONAL) (DOI: 10.17487/RFC5869)
On the proper way to use a keyed SHA2 hash as a KDF.
Hash chains build off a secret key are considered not safe.
For SHA3, KMAC (NIST SP800-185) is a proven KDF.
See:
https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-108r1-upd1.pdf
Sec 4.4.
I have had the privilege of direct conversations with Dr. Krawczyk even
prior to his presentation on keyed hash attacks in 1995 and the reason
for the HMAC (RFC2104) construct.
And I have had the privilege of following along with Team Keccak on the
development of what is now SHA3 and its derivatives. We are finally
seeing an uptick in replacing HMAC/HKDF with KMAC.
On 1/10/25 17:00, Sriram R via Cryptography-dev wrote:
Hello,
I'm generating a key using Scrypt from a password supplied by the
user. I then use this key as follows. This works but my question to
the experts: is this an acceptable way to use the AESGCMSIV cipher? Am
I doing something that's fundamentally against best practices? In the
examples on the Cryptography site, the sample code snippet uses
AESGCMSIV.generate_key() method to generate the key instead. The
requirement I have is to generate the key that's based on a password.
def gen_salt(size=32):
return secrets.token_bytes(size)
def der_key(salt, password):
kdf = Scrypt(salt=salt, length=32, n=2**20, r=8, p=1)
return kdf.derive(password.encode())
def gen_symmkey(salt, password):
symmkey = der_key(salt, password)
return symmkey
key = gen_symmkey(salt, password)
aesgcmsiv = AESGCMSIV(key)
ct = aesgcmsiv.encrypt(nonce, file_data, aad)
with open(fname, "wb") as outfile:
outfile.write(ct)
Best,
PE
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