What is a Cryptosystem?

Message to be disguised or encrypted. In communication systems, it may be a bit stream, such as text, bitmaps, digitized voice streams, or digitized video images.

A basic function of cryptographic technology is to achieve secure communication, a classic secure communication model

The methods used by cryptanalysts to decipher or attack ciphers include exhaustive attacks , statistical analysis, and

Assuming that the cryptanalyst knows all the knowledge of the encryption algorithm used, according to the cryptanalyst's mastery of data resources such as plaintext and ciphertext, the types of cryptanalysis attacks against encryption systems can be divided into the following four types:

There are three main factors to consider when measuring the complexity of cryptosystem attacks:

Kerckhoffs principle

Even if the algorithms in the cryptosystem are known to cryptanalysts, it is difficult to deduce the plaintext or key from the intercepted ciphertext.

In other words, the security of the cryptosystem should only depend on the confidentiality of the key, not on the confidentiality of the algorithm.

A password that is still secure is only assuming that the attacker has sufficient research on cryptographic algorithms and has sufficient computing resources to be a secure cryptosystem.

In a word: "Every secret lies in a key"

For commercial cryptosystems, the advantages of public crypto algorithms include:

Conducive to public testing and evaluation of the security of cryptographic algorithms;

Prevent designers of cryptographic algorithms from hiding the backdoor in the algorithm;

Easy to standardize cryptographic algorithms;

It is conducive to the large-scale production of cryptographic algorithm products, and achieves low cost and high performance.

However, it must be pointed out that the disclosure principle of password design does not mean that all passwords must disclose password algorithms when they are applied. For example, military and political core passwords of countries around the world do not disclose their encryption algorithms.

In summary, a cryptographic system that provides confidentiality services is actually available, and the basic requirements must be met:

The confidentiality of the system does not depend on the confidentiality of the encryption system or algorithm, but only on the security of the key. "Every secret lies in a key" is an important principle in the design of cryptosystems.

Satisfy the actual security, making it impossible for the decipherer to determine the key or the corresponding plaintext within the valid time and cost after obtaining the ciphertext.

The encryption and decryption algorithms should be applicable to all elements in the plain text space and key space.

The encryption and decryption algorithms can be calculated efficiently, and the cryptosystem is easy to implement and use. ^[2]