The methods of cryptanalyzers to decipher or attack passwords are mainly qiongju attack, statistical analysis and mathematical analysis.

### exhaustive attack

Exhaustive attack is also called brute force attack. This attack is to traverse all possible keys to the intercepted ciphertext until an understandable transformation from ciphertext to plaintext is obtained; Or encrypt all possible plaintexts with the same key until they are consistent with the intercepted ciphertext. Obviously, for any Cryptosystem with known cryptographic algorithm, as long as the attacker has enough computing resources, this method can be successful. Exhaustive attack is one of the most basic attack methods to password. The main methods against qiongju attack are: increasing the length of key, adding random redundant information in plaintext and ciphertext, etc.

### Statistical analysis

Statistical analysis attack is a method by which cryptanalysis deciphers the cipher according to the statistical laws of plaintext, ciphertext and key.

For example, in the classical transposition cipher and permutation cipher system, it can be deciphered by analyzing the frequency of single letter, double letter, three letter and other statistical parameters. The main way to resist statistical analysis attack is to make the statistical characteristics of plaintext not be replaced by ciphertext. In this way, the ciphertext does not have the trace of plaintext, but presents great randomness, thus defeating the statistical analysis attack. To be able to resist statistical analysis attacks has become the basic requirement of modern cryptography.

### Mathematical analysis

Mathematical analysis attack refers to the cryptanalyzer’s deciphering of the cipher by solving the mathematical problems according to the mathematical basis and some cryptographic characteristics of the encryption and decryption algorithm. Mathematical analysis attack is the main threat to various cryptographic algorithms based on mathematical problems. In order to resist this kind of attack, we should choose encryption algorithm with solid mathematical foundation and enough complexity.

There are four types of cryptanalysis attacks against encryption systems

- Ciphertext only attack
- Plaintext known attack
- Chosen plaintext attack
- Chosen ciphertext attack

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