The content and typical algorithm of symmetric cryptosystem

Content: In a symmetric encryption system, encryption and decryption use the same key. Because the encryption and decryption keys are the same, both parties who need to communicate must choose and save their same key, and each party must trust the other party not to disclose the key, so as to realize the confidentiality and integrity of data.

Algorithms: DES (Data Encryption Standard) algorithm and its variants Triple DES (Triple DES) and GDES (Generalized DES); Ideas; In Europe; FEAL N and RC5 in Japan.

Triple DES uses two independent 56-bit keys to encrypt the exchanged information three times, so that its effective length reaches 1 12 bits. RC2 and RC4 are patented symmetric encryption algorithms of RSA Data Security Company, which use variable key length algorithm. By specifying different key lengths, C2 and RC4 can improve or decrease the security.

Extended data:

Basic mode of cryptographic system:

The usual cryptosystem uses shift method, substitution method and algebraic method to transform encryption and decryption, and one or the combination of several methods can be used as the basic way of data transformation. The following example illustrates:

Displacement method is also called replacement method. The Shift method rearranges the characters in plain text, and the characters themselves remain unchanged, but their positions have changed.

For example, the simplest example: write the letters and characters in the text upside down.

Or send ciphertext with a fixed length.

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