Cryptography Stack Exchange is a question and answer site for software developers, mathematicians and others interested in cryptography. Join them; it only takes a minute:

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

If I have a string encoded with AES CBC with PKCS#5 padding, how can one possibly decrypt/crack it? What are the approaches that one can take to break its security?

share|improve this question
up vote 1 down vote accepted

You may take the following approaches:

  1. You can check if the key generation or storage has any weaknesses;
  2. You can check if padding oracle attacks apply;
  3. You can check if (part of) the ciphertext has been generated previously (using the same IV).

Neither of these methods work when AES CBC has been correctly applied. AES does provide adequate confidentiality, even for many ciphertext&plaintext pairs.

share|improve this answer
This answermay not be cover all attacks. – Maarten Bodewes Feb 14 '13 at 11:59
Thanks for your answer, would you help me understand padding oracle attacks better? All of the articles I found on the net were too 'mathematical'. I'd like to learn in with a practical approach. – Wise Feb 14 '13 at 18:13
A quick Google search already shows some results: – Maarten Bodewes Feb 14 '13 at 18:23

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.