# Tag Info

3

This can be broken. The exact nature of the attack will depend what modulus you use for the Hill cipher: are you working modulo a prime number, or working modulo 26? Working modulo a prime $p$ A simple attack, with no fancy mathematics needed. One simple attack is to start by requesting the encryption of the 26 messages AAAA, BBBB, CCCC, DDDD, ..., ZZZZ. ...

3

One possibility for what you might be missing: normally the same key (the same matrix) is re-used to encrypt many messages. So now try counting the total entropy in $M$ length-$N$ messages, and the entropy in a $N\times N$ matrix, and compare what happens when $M$ gets large.... Another possibility you might be missing is the consequences of the fact that ...

2

One time pad is definitely both easy to do and has perfect secrecy, but key management is a pain and can compromise security. Basically a Vigenère cipher with a key as long as the the message should be secure, because different keys can create ALL possible messages with equal probabilities. Again, it's a one time pad, so no KPA, CPA, or CCA security. ...

1

Linearizing should work fine. You'll have to make a minor adjustment to deal with the fact that we are working modulo 26, but either of the following two simple tweaks should work fine: You could use generalized Gaussian elimination, generalized to work over $\mathbb{Z}/26\mathbb{Z}$ (standard Gaussian elimination assumes we are working over a field, but ...

Only top voted, non community-wiki answers of a minimum length are eligible