Analysis of encryption in terms of its cryptographic strength. Cryptanalysis examines the possibilities of circumventing cryptographic protection. This involves cracking keys and specifically searching for weak points in the encryption. One well-known method is the brute force attack, in which all possible combinations of an encryption algorithm are systematically tried. There are other methods for cryptanalysis such as the algebraic attack, which attempts to represent the algorithm as a nonlinear system of equations, the attack with selected plaintext or with adaptive plaintext.
When cracking keys, a distinction is made between linear and differential cryptanalysis.
Linear cry ptanalysis targets the plaintext and attempts to determine simple, linear relationships between bits of plaintext and ciphertext in order to obtain information about the key. Such a plaintext attack attempts to determine statistical correlations between plaintext, ciphertext and cipher key. For this purpose, parts of the plaintext are combined with parts of the ciphertext in an XOR operation. In a plaintext attack, the attacker must know or be able to deduce parts of the plaintext. A possible attack could also be initiated by providing the sender with texts, which are then intercepted as ciphertexts and from which the key is derived.
In differential cryptanalysis, plaintexts are examined for certain distinctions and conclusions are drawn about the encryption algorithm. For this purpose, the differences between the ciphertexts compared in pairs are traced back over the DES encry ption performed several times and the cipher key is calculated from this. The differential cryptanalysis method was published by Adi Shamir in 1990.
A cryptanalysis that analyzes only ciphertexts is called a ciphertext attack. In this case, the attacker tries to draw conclusions about the plaintext from statistical analyses.
There are various methods for cryptanalysis. Some are based on the analysis of performance characteristics, the Power Analysis. These include Simple Power Analysis( SPA), Differential Power Analysis( DPA) and Differential Fault Analysis( DFA).