Cryptanalysis is the process of analyzing the ciphertext or cryptogram to discover the actual text (plaintext) or the key used in the cryptosystem. There are a number of strategies to do this but the chosen strategy usually depends on the characteristics of the encryption scheme used and how much information is available about the ciphertext.
An encryption scheme is considered to be secure if the ciphertext created using the cryptanalysis methods could not provide enough details or information that can be helpful in determining the corresponding plaintext.
The types of attacks are:
- Ciphertext only
- Known plaintext
- Chosen plaintext
- Chosen ciphertext
In ciphertext only attack, only the ciphertext is available for analysis. The attacker do not have any other knowledge about the actual message.
In the known plaintext attack, the plaintext and ciphertext pair(s) is(are) available. The secret key is not known.
In the chosen plaintext attack, the pair of plaintext and ciphertext is available. The attacker may have temporary access to the encryption process and therefore can choose plaintexts and generate the corresponding ciphertexts. The possibility of such an attack is not high. Systems that can withstand such an attack is considered very secure. In this type of attacks, the goal is to recover the secret key.
In the chosen ciphertext attack, the attacker can choose a random ciphertext and find some information from the corresponding decrypted plaintext. In this type of attack, the attacker may have temporary access to the decryption process. During this temporary availability, the attacker can choose ciphertexts and generate the corresponding plaintexts.
