diff options
Diffstat (limited to 'src/add_python/lilliput/ae_mode_1.py')
| -rw-r--r-- | src/add_python/lilliput/ae_mode_1.py | 25 |
1 files changed, 12 insertions, 13 deletions
diff --git a/src/add_python/lilliput/ae_mode_1.py b/src/add_python/lilliput/ae_mode_1.py index 4a40b78..197bf37 100644 --- a/src/add_python/lilliput/ae_mode_1.py +++ b/src/add_python/lilliput/ae_mode_1.py @@ -52,27 +52,26 @@ def _lower_nibble(i): return i & 0b00001111 -def _byte_from_nibbles(lower, upper): - return upper<<4 | lower +def _byte(high, low): + return high<<4 ^ low def _tweak_message(N, j, prefix): - # j is encoded on 68 bits; get 72 and clear the upper 4. - j_len = (TWEAK_BITS-NONCE_BITS-4)//8 + 1 - tweak = integer_to_byte_array(j, j_len) - tweak[-1] &= 0b00001111 + tweak = [_byte(prefix.value, _upper_nibble(N[0]))] - # Add nonce. - tweak[-1] |= _lower_nibble(N[0]) << 4 tweak.extend( - _byte_from_nibbles(_upper_nibble(N[i-1]), _lower_nibble(N[i])) + _byte(_lower_nibble(N[i-1]), _upper_nibble(N[i])) for i in range(1, NONCE_BITS//8) ) - # Add last nibble from nonce and prefix. - tweak.append( - _byte_from_nibbles(_upper_nibble(N[-1]), prefix.value) - ) + # j is encoded on 68 bits; get 72 then set the upper 4 to the + # nonce's lower 4. + j_len = (TWEAK_BITS-NONCE_BITS-4)//8 + 1 + j_array = integer_to_byte_array(j, j_len) + j_array[0] &= 0b00001111 + j_array[0] |= _lower_nibble(N[-1]) << 4 + + tweak.extend(j_array) return tweak |