103 lines
1.9 KiB
Python
103 lines
1.9 KiB
Python
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#
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# bignum.py
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#
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# This file is copied from python-bitcoinlib.
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#
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# Distributed under the MIT/X11 software license, see the accompanying
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# file COPYING or http://www.opensource.org/licenses/mit-license.php.
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#
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"""Bignum routines"""
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from __future__ import absolute_import, division, print_function, unicode_literals
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import struct
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# generic big endian MPI format
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def bn_bytes(v, have_ext=False):
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ext = 0
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if have_ext:
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ext = 1
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return ((v.bit_length()+7)//8) + ext
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def bn2bin(v):
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s = bytearray()
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i = bn_bytes(v)
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while i > 0:
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s.append((v >> ((i-1) * 8)) & 0xff)
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i -= 1
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return s
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def bin2bn(s):
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l = 0
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for ch in s:
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l = (l << 8) | ch
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return l
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def bn2mpi(v):
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have_ext = False
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if v.bit_length() > 0:
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have_ext = (v.bit_length() & 0x07) == 0
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neg = False
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if v < 0:
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neg = True
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v = -v
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s = struct.pack(b">I", bn_bytes(v, have_ext))
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ext = bytearray()
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if have_ext:
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ext.append(0)
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v_bin = bn2bin(v)
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if neg:
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if have_ext:
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ext[0] |= 0x80
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else:
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v_bin[0] |= 0x80
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return s + ext + v_bin
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def mpi2bn(s):
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if len(s) < 4:
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return None
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s_size = bytes(s[:4])
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v_len = struct.unpack(b">I", s_size)[0]
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if len(s) != (v_len + 4):
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return None
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if v_len == 0:
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return 0
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v_str = bytearray(s[4:])
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neg = False
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i = v_str[0]
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if i & 0x80:
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neg = True
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i &= ~0x80
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v_str[0] = i
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v = bin2bn(v_str)
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if neg:
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return -v
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return v
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# bitcoin-specific little endian format, with implicit size
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def mpi2vch(s):
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r = s[4:] # strip size
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r = r[::-1] # reverse string, converting BE->LE
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return r
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def bn2vch(v):
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return bytes(mpi2vch(bn2mpi(v)))
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def vch2mpi(s):
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r = struct.pack(b">I", len(s)) # size
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r += s[::-1] # reverse string, converting LE->BE
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return r
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def vch2bn(s):
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return mpi2bn(vch2mpi(s))
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