new file: mmgen/contrib/descriptors.py

mmgen/contrib/descriptors.py

@@ -0,0 +1,64 @@
+#!/usr/bin/env python3
+# Copyright (c) 2019 Pieter Wuille
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+"""Utility functions related to output descriptors"""
+
+import re
+
+INPUT_CHARSET = "0123456789()[],'/*abcdefgh@:$%{}IJKLMNOPQRSTUVWXYZ&+-.;<=>?!^_|~ijklmnopqrstuvwxyzABCDEFGH`#\"\\ "
+CHECKSUM_CHARSET = "qpzry9x8gf2tvdw0s3jn54khce6mua7l"
+GENERATOR = [0xf5dee51989, 0xa9fdca3312, 0x1bab10e32d, 0x3706b1677a, 0x644d626ffd]
+
+def descsum_polymod(symbols):
+    """Internal function that computes the descriptor checksum."""
+    chk = 1
+    for value in symbols:
+        top = chk >> 35
+        chk = (chk & 0x7ffffffff) << 5 ^ value
+        for i in range(5):
+            chk ^= GENERATOR[i] if ((top >> i) & 1) else 0
+    return chk
+
+def descsum_expand(s):
+    """Internal function that does the character to symbol expansion"""
+    groups = []
+    symbols = []
+    for c in s:
+        if not c in INPUT_CHARSET:
+            return None
+        v = INPUT_CHARSET.find(c)
+        symbols.append(v & 31)
+        groups.append(v >> 5)
+        if len(groups) == 3:
+            symbols.append(groups[0] * 9 + groups[1] * 3 + groups[2])
+            groups = []
+    if len(groups) == 1:
+        symbols.append(groups[0])
+    elif len(groups) == 2:
+        symbols.append(groups[0] * 3 + groups[1])
+    return symbols
+
+def descsum_create(s):
+    """Add a checksum to a descriptor without"""
+    symbols = descsum_expand(s) + [0, 0, 0, 0, 0, 0, 0, 0]
+    checksum = descsum_polymod(symbols) ^ 1
+    return s + '#' + ''.join(CHECKSUM_CHARSET[(checksum >> (5 * (7 - i))) & 31] for i in range(8))
+
+def descsum_check(s, require=True):
+    """Verify that the checksum is correct in a descriptor"""
+    if not '#' in s:
+        return not require
+    if s[-9] != '#':
+        return False
+    if not all(x in CHECKSUM_CHARSET for x in s[-8:]):
+        return False
+    symbols = descsum_expand(s[:-9]) + [CHECKSUM_CHARSET.find(x) for x in s[-8:]]
+    return descsum_polymod(symbols) == 1
+
+def drop_origins(s):
+    '''Drop the key origins from a descriptor'''
+    desc = re.sub(r'\[.+?\]', '', s)
+    if '#' in s:
+        desc = desc[:desc.index('#')]
+    return descsum_create(desc)