Cryptography Tackling AES side channel attack on algorithmic level with altered key expansion. |
| Tackling AES side channel attack on algorithmic level with altered key expansion. Posted: 13 Sep 2018 10:08 AM PDT AES has a key expansion that expands the sub keys from the beginning of the encryption pipeline towards the end. This key expansion is also reversible ie. if only decryption is done in a specific HW all the sub keys can be calculated from the first decryption sub key as well, which is btw. the last sub key of the encryption. Power analysis side channel attacks target this first layer sub key and then calculate the entire set of sub keys of it. I thought of a key expansion - in a theoretical, new algorithm for side channel attack prone systems - that uses a key expansion, which is irreversible, like a hash. Then if the middle pair of sub keys are expanded first and then symmetrically till the first and last sub key, then the attacker has to go on reverse engineering at least half of the sub keys one by one. So like: subKey0<=subKey1<=…<=subKey4<=MAIN_KEY=>subKey5=>subKey6=>…=>subKey9 where every "<=" and "=>" has to be an irreversible expansion step. I believe it should be possible to reverse engineer all the sub keys even this way but at least it can be made arbitrarily harder: for a low data rate system, like a challenge response's hardware key based authentication, an encryption with for example a 1000 sub keys can be constructed, so that then at least 500 sub keys will have to be reverse engineered… Some links I based this idea on: https://www.tandfonline.com/doi/full/10.1080/23742917.2016.1231523 https://www.youtube.com/watch?v=FktI4qSjzaE&t=27s EDIT: composition [link] [comments]  |
| Triple-Encrypted Vigenere - Please try to crack it Posted: 13 Sep 2018 09:31 AM PDT Please do not post in this thread if you are offended by me comparing this cipher to One-Time Pad.I read that if you use multiple keys whose lengths are relatively prime to encrypt Vigenere, the normal attacks on it won't work even when the ciphertext is longer than the sum of all the keys, as long as it's shorter than the product of all the keys. This implies that one may turn a Vigenere into something comparable to a One-Time Pad, but without the need for a key as big as the message. I posted a challenge in /r/cryptography but nobody was able to complete it, so I'm trying here again with a smaller sample. The keys are of lengths 13, 14, 15 (LCM = 2730). The keys are composed of 2 English words each. The ciphertext is English and 2030 letters long. It was encrypted using this reciprocal tabula recta (called DIANA). Here is the ciphertext: I wasn't sure whether to post this here or in /r/codes. If anyone needs Javascript to help them automate a process that helps them decrypt this, I'm more than happy to write that for you since I really, really, really want to see this system broken (if it actually can be!).
Update: I have edited this post with new ciphertext made from new keys whose lengths are relatively prime. [link] [comments]  |
| You are subscribed to email updates from Cryptography news and discussions. To stop receiving these emails, you may unsubscribe now. | Email delivery powered by Google |
| Google, 1600 Amphitheatre Parkway, Mountain View, CA 94043, United States | |
No comments:
Post a Comment