base32hex.py

# implementation of RFC 4648 using extended hex alphabet
# https://tools.ietf.org/html/rfc4648#page-10
# Used by golang in a number of places but doesn't seem to
# exist in the standard library.

encodeHex = "0123456789ABCDEFGHIJKLMNOPQRSTUV"

decodeHexMap = {}
for index, i in enumerate(encodeHex):
    decodeHexMap[i] = index

padChar = "="

class BadPadding(Exception):
    pass

def encode(src, str_map):
    dst = []
    src_len = 0

    if len(src) == 0:
        return ''

    while len(src):
        src_len = len(src)
        next_byte = [0] * 8

        if src_len > 4:
            next_byte[7] = src[4] & 0x1f
            next_byte[6] = src[4] >> 5

        if src_len > 3:
            next_byte[6] = next_byte[6] | (src[3] << 3) & 0x1f
            next_byte[5] = (src[3] >> 2) & 0x1f
            next_byte[4] = src[3] >> 7

        if src_len > 2:
            next_byte[4] = next_byte[4] | (src[2] << 1) & 0x1f
            next_byte[3] = (src[2] >> 4) & 0x1f

        if src_len > 1:
            next_byte[3] = next_byte[3] | (src[1] << 4) & 0x1f
            next_byte[2] = (src[1] >> 1) & 0x1f
            next_byte[1] = (src[1] >> 6) & 0x1f

        if src_len > 0:
            next_byte[1] = next_byte[1] | (src[0] << 2) & 0x1f
            next_byte[0] = src[0] >> 3

        for nb in next_byte:
            dst.append(str_map[nb])

        src = src[5:]

    if src_len < 5:
        dst[-1] = '='
    if src_len < 4:
        dst[-2] = '='
        dst[-3] = '='
    if src_len < 3:
        dst[-4] = '='
    if src_len < 2:
        dst[-5] = '='
        dst[-6] = '='

    return ''.join(dst)

def decode(src, str_map):
    src = src.upper()

    end = False
    result = []
    while len(src) > 0 and not end:
        dst = [0] * 5
        dbuf = [0] * 8

        src_len = 8

        for i in range(0, 8):
            if i >= len(src):
                src_len = i
                end = True
                break
            char = src[i]
            if char == padChar:
                end = True
                src_len = i
                break
            else:
                dbuf[i] = decodeHexMap[char]


        if src_len >= 8:
            dst[4] = (dbuf[6] << 5) | (dbuf[7])
        if src_len >= 7:
            dst[3] = (dbuf[4] << 7) | (dbuf[5] << 2) | (dbuf[6] >> 3)
        if src_len >= 5:
            dst[2] = (dbuf[3] << 4) | (dbuf[4] >> 1)
        if src_len >= 4:
            dst[1] = (dbuf[1] << 6) | (dbuf[2] << 1) | (dbuf[3] >> 4)
        if src_len >= 2:
            dst[0] = (dbuf[0] << 3) | (dbuf[1] >> 2)

        dst = map(lambda x: x & 0xff, dst)

        if src_len == 2:
            dst = dst[:1]
        elif src_len == 4:
            dst = dst[:2]
        elif src_len == 5:
            dst = dst[:3]
        elif src_len == 7:
            dst = dst[:4]
        elif src_len == 8:
            dst = dst[:5]

        result.extend(dst)
        src = src[8:]

    return result
    

def base32hex_encode(src):
    return encode(src, encodeHex)

def base32hex_decode(src):
    return decode(src, encodeHex)