Super User is a question and answer site for computer enthusiasts and power users. 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 know that with brute force there are 2^56 possible keys to check (56 bits, each either a 1 or 0). But let's say I know the message itself is only made up of letters (a-z, A-Z).

Would knowing things (like the limitation to just letters) about the plaintext make breaking the encryption easier?

share|improve this question
up vote 2 down vote accepted

The answer is a vague YES, as this depends on the encryption algorithm. This is usually also a function of the number of cipher and plain-text messages available (in most cases the more such available, the easier it is to break the code).

This is the reason that 56-bits is today counted as very weak protection, especially in view of the computing-power available to government organizations.

For the RSA method quoted by bbaja42, see RSA Algorithm section "Weaknesses in RSA", as well as Cracking RSA and RSA: Hacking and Cracking.

share|improve this answer
thanks for info – bbaja42 Dec 10 '10 at 21:23

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

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