I am working on one interesting question. There is a ciphertext that has 10,000 letters. We need to distingish whether this ciphertext was encrypted by a transposition cipher or a simple subsitution cipher.
I understand a transposition cipher will keep the identity of each letter and a substitution cipher will change the letter to something new. So, I think we could probably check the common English patterns in the ciphertext (like 'ing', 'th', etc). If those patterns exist, we could conclude that this is a subsitution cipher. Otherwise, it would be a transposition cipher. However, this answer is not convincing for me. I hope to get an answer from an expert.