Kerckhoffs 原则


Shannon Security(Perfect Secrecy)

Ciphertext should reveal no "infomation" about Plaintext:Pr[PT=m|CT=c]=Pr[PT=m]

The resulting ciphertext will be impossible to deccrypt or break if the following four conditions are met:

  1. The key must at least as long as the plaintext.
  2. The key must be random.
  3. The key must never be reused in whole or in part.
  4. The key must be kept completely secret by the communicating parties.

One-time pad(OTP)

In cryptography, the one-time pad (OTP) is an encryption technique that cannot be cracked, but requires the use of a single-use pre-shared key that is not smaller than the message being sent.

Pseudo Random Number Generator(PRNG)

Stream Cipher

Block Cipher

Hash function

Requirements for Cryptographic Hash Functions

Usages of Cryptographics Hash Functions


Security level

The level of security of a hash function that output n bits, is about n/2 bits.

Message Authentication Code(MAC)

Public-Key Encryption