src/trezor/crypto: add trezor.crypto.base32

src/trezor/crypto/base32.py

@@ -0,0 +1,97 @@
+# Base32 implementation taken from the micropython-lib's base64 module
+# https://github.com/micropython/micropython-lib/blob/master/base64/base64.py
+#
+
+from ubinascii import unhexlify
+from ustruct import unpack
+
+
+_b32alphabet = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ234567'
+
+_b32tab = [ord(c) for c in _b32alphabet]
+_b32rev = dict([(ord(v), k) for k, v in enumerate(_b32alphabet)])
+
+
+def encode(s: bytes) -> str:
+    quanta, leftover = divmod(len(s), 5)
+    # Pad the last quantum with zero bits if necessary
+    if leftover:
+        s = s + bytes(5 - leftover)  # Don't use += !
+        quanta += 1
+    encoded = bytearray()
+    for i in range(quanta):
+        # c1 and c2 are 16 bits wide, c3 is 8 bits wide.  The intent of this
+        # code is to process the 40 bits in units of 5 bits.  So we take the 1
+        # leftover bit of c1 and tack it onto c2.  Then we take the 2 leftover
+        # bits of c2 and tack them onto c3.  The shifts and masks are intended
+        # to give us values of exactly 5 bits in width.
+        c1, c2, c3 = unpack('!HHB', s[i*5:(i+1)*5])
+        c2 += (c1 & 1) << 16 # 17 bits wide
+        c3 += (c2 & 3) << 8  # 10 bits wide
+        encoded += bytes([_b32tab[c1 >> 11],         # bits 1 - 5
+                          _b32tab[(c1 >> 6) & 0x1f], # bits 6 - 10
+                          _b32tab[(c1 >> 1) & 0x1f], # bits 11 - 15
+                          _b32tab[c2 >> 12],         # bits 16 - 20 (1 - 5)
+                          _b32tab[(c2 >> 7) & 0x1f], # bits 21 - 25 (6 - 10)
+                          _b32tab[(c2 >> 2) & 0x1f], # bits 26 - 30 (11 - 15)
+                          _b32tab[c3 >> 5],          # bits 31 - 35 (1 - 5)
+                          _b32tab[c3 & 0x1f],        # bits 36 - 40 (1 - 5)
+                          ])
+    # Adjust for any leftover partial quanta
+    if leftover == 1:
+        encoded = encoded[:-6] + b'======'
+    elif leftover == 2:
+        encoded = encoded[:-4] + b'===='
+    elif leftover == 3:
+        encoded = encoded[:-3] + b'==='
+    elif leftover == 4:
+        encoded = encoded[:-1] + b'='
+
+    return bytes(encoded).decode()
+
+
+def decode(s: str) -> bytes:
+    s = s.encode()
+    quanta, leftover = divmod(len(s), 8)
+    if leftover:
+        raise ValueError('Incorrect padding')
+    # Strip off pad characters from the right.  We need to count the pad
+    # characters because this will tell us how many null bytes to remove from
+    # the end of the decoded string.
+    padchars = s.find(b'=')
+    if padchars > 0:
+        padchars = len(s) - padchars
+        s = s[:-padchars]
+    else:
+        padchars = 0
+
+    # Now decode the full quanta
+    parts = []
+    acc = 0
+    shift = 35
+    for c in s:
+        val = _b32rev.get(c)
+        if val is None:
+            raise ValueError('Non-base32 digit found')
+        acc += _b32rev[c] << shift
+        shift -= 5
+        if shift < 0:
+            parts.append(unhexlify(('%010x' % acc).encode()))
+            acc = 0
+            shift = 35
+    # Process the last, partial quanta
+    last = unhexlify(bytes('%010x' % acc, "ascii"))
+    if padchars == 0:
+        last = b''                      # No characters
+    elif padchars == 1:
+        last = last[:-1]
+    elif padchars == 3:
+        last = last[:-2]
+    elif padchars == 4:
+        last = last[:-3]
+    elif padchars == 6:
+        last = last[:-4]
+    else:
+        raise ValueError('Incorrect padding')
+    parts.append(last)
+    return b''.join(parts)

tests/test_trezor.crypto.base32.py

@@ -0,0 +1,46 @@
+from common import *
+from trezor.crypto import base32
+
+
+class TestCryptoBase32(unittest.TestCase):
+
+    # test vectors from:
+    # https://tools.ietf.org/html/rfc4648
+    # https://github.com/emn178/hi-base32/blob/master/tests/test.js
+    vectors = [
+        (b'', ''),
+        (b'f', 'MY======'),
+        (b'fo', 'MZXQ===='),
+        (b'foo', 'MZXW6==='),
+        (b'foob', 'MZXW6YQ='),
+        (b'fooba', 'MZXW6YTB'),
+        (b'foobar', 'MZXW6YTBOI======'),
+
+        (b'H', 'JA======'),
+        (b'He', 'JBSQ===='),
+        (b'Hel', 'JBSWY==='),
+        (b'Hell', 'JBSWY3A='),
+        (b'Hello', 'JBSWY3DP'),
+
+        (b'zlutoucky kun upel dabelske ody', 'PJWHK5DPOVRWW6JANN2W4IDVOBSWYIDEMFRGK3DTNNSSA33EPE======'),
+
+        (b'中文', '4S4K3ZUWQ4======'),
+        (b'中文1', '4S4K3ZUWQ4YQ===='),
+        (b'中文12', '4S4K3ZUWQ4YTE==='),
+        (b'aécio', 'MHB2SY3JN4======'),
+        (b'𠜎', '6CQJZDQ='),
+        (b'Base64是一種基於64個可列印字元來表示二進制資料的表示方法',
+         'IJQXGZJWGTTJRL7EXCAOPKFO4WP3VZUWXQ3DJZMARPSY7L7FRCL6LDNQ4WWZPZMFQPSL5BXIUGUOPJF24S5IZ2MAWLSYRNXIWOD6NFUZ46NIJ2FBVDT2JOXGS246NM4V')
+    ]
+
+    def test_encode(self):
+        for a, b in self.vectors:
+            self.assertEqual(base32.encode(a), b)
+
+    def test_decode(self):
+        for a, b in self.vectors:
+            self.assertEqual(base32.decode(b), a)
+
+
+if __name__ == '__main__':
+    unittest.main()