111 lines
2.7 KiB
Python
111 lines
2.7 KiB
Python
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"""
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RFC 6979:
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Deterministic Usage of the Digital Signature Algorithm (DSA) and
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Elliptic Curve Digital Signature Algorithm (ECDSA)
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http://tools.ietf.org/html/rfc6979
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Many thanks to Coda Hale for his implementation in Go language:
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https://github.com/codahale/rfc6979
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"""
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import hmac
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from binascii import hexlify
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from .util import number_to_string, number_to_string_crop, bit_length
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from ._compat import hmac_compat
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# bit_length was defined in this module previously so keep it for backwards
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# compatibility, will need to deprecate and remove it later
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__all__ = ["bit_length", "bits2int", "bits2octets", "generate_k"]
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def bits2int(data, qlen):
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x = int(hexlify(data), 16)
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l = len(data) * 8
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if l > qlen:
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return x >> (l - qlen)
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return x
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def bits2octets(data, order):
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z1 = bits2int(data, bit_length(order))
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z2 = z1 - order
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if z2 < 0:
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z2 = z1
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return number_to_string_crop(z2, order)
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# https://tools.ietf.org/html/rfc6979#section-3.2
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def generate_k(order, secexp, hash_func, data, retry_gen=0, extra_entropy=b""):
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"""
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order - order of the DSA generator used in the signature
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secexp - secure exponent (private key) in numeric form
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hash_func - reference to the same hash function used for generating
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hash
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data - hash in binary form of the signing data
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retry_gen - int - how many good 'k' values to skip before returning
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extra_entropy - extra added data in binary form as per section-3.6 of
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rfc6979
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"""
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qlen = bit_length(order)
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holen = hash_func().digest_size
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rolen = (qlen + 7) // 8
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bx = (
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hmac_compat(number_to_string(secexp, order)),
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hmac_compat(bits2octets(data, order)),
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hmac_compat(extra_entropy),
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)
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# Step B
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v = b"\x01" * holen
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# Step C
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k = b"\x00" * holen
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# Step D
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k = hmac.new(k, digestmod=hash_func)
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k.update(v + b"\x00")
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for i in bx:
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k.update(i)
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k = k.digest()
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# Step E
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v = hmac.new(k, v, hash_func).digest()
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# Step F
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k = hmac.new(k, digestmod=hash_func)
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k.update(v + b"\x01")
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for i in bx:
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k.update(i)
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k = k.digest()
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# Step G
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v = hmac.new(k, v, hash_func).digest()
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# Step H
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while True:
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# Step H1
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t = b""
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# Step H2
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while len(t) < rolen:
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v = hmac.new(k, v, hash_func).digest()
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t += v
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# Step H3
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secret = bits2int(t, qlen)
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if 1 <= secret < order:
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if retry_gen <= 0:
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return secret
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retry_gen -= 1
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k = hmac.new(k, v + b"\x00", hash_func).digest()
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v = hmac.new(k, v, hash_func).digest()
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