Structural Properties of Cryptographic Sequences - Computational Intelligence in Security for Information Systems - page 188

Table 1. Avalanche results for the proposed expansion scheme

Digest Size Rounds Expanded Size Expanded Ratio Avalanche
224 72 144(14) 10.9% 49%

256 80 160(30) 23.4% 50%

384 96 192(62) 48.4% 50%

512 112 224(94) 73.4% 50%

768 128 256(126) 98.4% 50%

1024 144 288(158) 123.4% 50%

Table 2. Performance values in cycles per byte

Digest Speed
224 10.79 cpb
256 12.53 cpb
384 15.94 cpb
512 19.36 cpb
768 22.69 cpb
1024 26.06 cpb

4 Future Work

Although the proposed message expansion presents many favorable properties
and is designed to prevent known collision attacks against Tangle, there are still
other areas were Tangle can be improved:

- In the smaller digest sizes, the expansion ratio is very small and not all
message words are used as input to generate the expanded message words.
This implies that the actual expanded message could be very similar in
whole to another similar message since the message is itself included in the
expanded version and consumes a considerable amount of space. This is
somewhat circumvented by the use of the S-Box in the message expansion
to choose a constant.
- The current order of the words contained in the expanded message maximizes
differences but putting the second pseudo CRC at the end of the message
might be more secure, leaving an attacker limited control of the initial and
final parts of the expanded message.
- The round function and output function should be modified too. This is a
work currently in progress.
- Tangle could benefit by a redesign with a 64 bit platform in mind. This type
of platform is more common today than when Tangle was originally designed
and is something under study.