How to identify encryption algorithm used in ciphertext?

Question

Is there any ways to try to guess encryption algorithm used to encrypt the ciphertext?

Answer 1

Yes. There are some differences:

• Is it a block cipher or not can be guessed from the length.
• Block length
• Entropy of the output (are all characters equally present? / can patterns be found?)
• Recurrences (CBC or not...)

The entropy of the string is probably the best hint. A simple method to determine it is probably trying to compress it. Some methods can be found here: http://www.random.org/statistics/ They use them to make sure their numbers are as random as possible.

I've got no idea if it's really possible to determine the encryption using these methods.