101 lines
1.9 KiB
101 lines
1.9 KiB
#!/usr/bin/env python3 |
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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 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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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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