Information Security Stack Exchange is a question and answer site for information security professionals. It's 100% free, no registration required.

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

I've been reading about solitare and its weaknesses, and thinking about clever ways of hiding keys. It seems like you could encode an 52-bit AES key in the vertical orientation of cards in a deck (or 104-bit if it wouldn't be suspicious that you have cards flipped back-to-front).

What I'm wondering is, would it be safe to just zero-pad the rest of the key, or are there problems if part of the key is known? A more practical comparison seems to be AES-128 and AES-256: If I padded a 128-bit AES key for AES-256, would it be weaker than the original key with AES-128?

share|improve this question

closed as off-topic by Adi, NULLZ, Xander, bethlakshmi, TildalWave Jul 24 '13 at 14:11

  • This question does not appear to be about Information security within the scope defined in the help center.
If this question can be reworded to fit the rules in the help center, please edit the question.

Might be best on – Michael Jul 24 '13 at 10:49
This question appears to be off-topic because it belongs to Crypto.SE – Adi Jul 24 '13 at 11:53
up vote 5 down vote accepted

There is no known weakness in having a "padded key" for AES, besides the obvious weakness of the key space size being reduced (a 52-bit key space can be explored exhaustively with some PC and some patience). However, AES security was not studied thoroughly for that kind of property, so anything goes; for instance, AES is known to be relatively flaky with regards to related key attacks, which operate in a similar area. To be safer, consider hashing your key elements with SHA-256, and using the hash output as key for AES.

share|improve this answer

Not the answer you're looking for? Browse other questions tagged or ask your own question.