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34 lines
953 B
34 lines
953 B
2 years ago
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#!/usr/bin/env python3
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# Copyright (c) 2023 The Bitcoin Core developers
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# Distributed under the MIT software license, see the accompanying
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# file COPYING or http://www.opensource.org/licenses/mit-license.php.
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"""Test-only HKDF-SHA256 implementation
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It is designed for ease of understanding, not performance.
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WARNING: This code is slow and trivially vulnerable to side channel attacks. Do not use for
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anything but tests.
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"""
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import hashlib
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import hmac
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def hmac_sha256(key, data):
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"""Compute HMAC-SHA256 from specified byte arrays key and data."""
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return hmac.new(key, data, hashlib.sha256).digest()
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def hkdf_sha256(length, ikm, salt, info):
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"""Derive a key using HKDF-SHA256."""
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if len(salt) == 0:
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salt = bytes([0] * 32)
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prk = hmac_sha256(salt, ikm)
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t = b""
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okm = b""
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for i in range((length + 32 - 1) // 32):
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t = hmac_sha256(prk, t + info + bytes([i + 1]))
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okm += t
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return okm[:length]
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