Cryptography Stack Exchange is a question and answer site for software developers, mathematicians and others interested in cryptography. 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

These days I'm reading about quantum computing and quantum cryptography which I've found extremely interesting. Well, I also read some blog posts of Bruce Schneier talking about how quantum computers threaten our current asymmetric crypto-systems. However, I don't know whether quantum computers also threaten symmetric crypto-systems (AES, Vernam cipher, etc.).

share|improve this question
up vote 7 down vote accepted

With Grover's algorithm, quantum computers can brute-force a block cipher with $n$-bit keys using $2^{n/2}$ steps, which is much smaller than the regular effort ($2^n$). This means, for example, that AES-128 could be broken with $2^{64}$ steps, and that AES-256 would offer the same security that AES-128 offers currently.

In short, key sizes would need to be doubled.

share|improve this answer

Your Answer

 
discard

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