From 5bb510b589cd0ec6876b1aca68587035eefd7696 Mon Sep 17 00:00:00 2001 From: Mark Qvist Date: Tue, 7 Jun 2022 15:26:45 +0200 Subject: [PATCH] Added internal python-only HKDF --- RNS/Cryptography/HKDF.py | 35 +++++++++++++++++++++++++++++++++++ 1 file changed, 35 insertions(+) create mode 100644 RNS/Cryptography/HKDF.py diff --git a/RNS/Cryptography/HKDF.py b/RNS/Cryptography/HKDF.py new file mode 100644 index 0000000..dddcbdf --- /dev/null +++ b/RNS/Cryptography/HKDF.py @@ -0,0 +1,35 @@ +import hashlib +from math import ceil +from RNS.Cryptography import HMAC + +def hkdf(length=None, derive_from=None, salt=None, context=None): + hash_len = 32 + + def hmac_sha256(key, data): + return HMAC.new(key, data, hashlib.sha256).digest() + + if length == None or length < 1: + raise ValueError("Invalid output key length") + + if derive_from == "None" or derive_from == "": + raise ValueError("Cannot derive key from empty input material") + + if salt == None or len(salt) == 0: + salt = bytes([0] * hash_len) + + if salt == None: + salt = b"" + + if context == None: + context = b"" + + pseudorandom_key = hmac_sha256(salt, derive_from) + + block = b"" + derived = b"" + + for i in range(ceil(length / hash_len)): + block = hmac_sha256(pseudorandom_key, block + context + bytes([i + 1])) + derived += block + + return derived[:length] \ No newline at end of file