35 lines
899 B
Python
35 lines
899 B
Python
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import hashlib
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from math import ceil
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from RNS.Cryptography import HMAC
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def hkdf(length=None, derive_from=None, salt=None, context=None):
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hash_len = 32
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def hmac_sha256(key, data):
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return HMAC.new(key, data, hashlib.sha256).digest()
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if length == None or length < 1:
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raise ValueError("Invalid output key length")
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if derive_from == "None" or derive_from == "":
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raise ValueError("Cannot derive key from empty input material")
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if salt == None or len(salt) == 0:
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salt = bytes([0] * hash_len)
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if salt == None:
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salt = b""
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if context == None:
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context = b""
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pseudorandom_key = hmac_sha256(salt, derive_from)
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block = b""
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derived = b""
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for i in range(ceil(length / hash_len)):
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block = hmac_sha256(pseudorandom_key, block + context + bytes([i + 1]))
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derived += block
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return derived[:length]
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