cryptanalysis

Cryptanalysis is an art or method of encrypted messages without knowing the key. It is the study of ciphers, ciphertext, or cryptosystems with the aim of understanding how they work and finding and improving techniques for defeating or weakening them. It is used to breach cryptographic security systems and gain access to the contents of encrypted messages, even if the cryptographic key is unknown.

It is of two types:

• ciphertext only attack: In this type of attack, the attacker has access to the ciphertext but not the plaintext. The attacker tries to find the plaintext or the key.
• known plaintext attack: In this type of attack, the attacker has access to the ciphertext and some of the plaintext. The attacker tries to find the key.

Cryptanalysis is of two forms:

• Linear Cryptanalysis: Linear cryptanalysis is a statistical attack technique used to analyze the linear relationship between the plaintext, ciphertext, and the key of a symmetric encryption algorithm. It exploits the linearity of the algorithm's components, such as substitution boxes (S-boxes) and linear transformations, to recover the key. This includes

  • contructing linear approximations
  • collecting ciphertext-plaintext pairs
  • finding key bits that can be exploited
  • expanding the key(deduce more bits of key)

• Differential Cryptanalysis: Differential cryptanalysis is statistical attack technique that aims to exploit the behavior of the differences between pairs of plaintexts, ciphertexts, and the corresponding subkeys in a symmetric encryption algorithm. It focuses on analyzing the differences rather than the linear relationships in the algorithm.This includes

  • creating differential characterstics
  • collect ciphertext plaintext pairs
  • find subkeys bits
  • recover complete key using knowledge of subkeys