Cryptography Beginner (i) basic concepts and DES encryption algorithm

1th Chapter

Encryption-Decryption

Decipher

PlainText-redaction

Secret key

Cryptographic algorithms

Symmetric password-public key password (asymmetric password)

One-way hash function-hash value

Message Authentication Code

Digital signatures

Pseudo-random number generator

The corresponding diagram of the threat and cipher technology in information security

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Implicit writing technique

Digital watermark

Do not use a secret cipher algorithm

Password algorithm password early evening to the show

Developing high-strength cryptographic algorithms is very difficult.

Using low-strength passwords is more dangerous than not doing task encryption

Any password will be cracked someday.

2nd Chapter

Caesar Password: The alphabet is encrypted with a certain number of rows "panning". The use of brute force cracking is easy to decrypt.

Simple replacement Password: Use the letter substitution table for encryption. Use brute force and frequency analysis to decipher passwords.

Enigma:

Enigma is a machine consisting of a keyboard, a gear, and a battery box bulb.

The daily password is recorded by the IDF password

Enigma's Weaknesses:

The communication password is entered continuously and encrypted two times.

The communication password is artificially selected.

An IDF code book must be distributed.

3rd. Symmetric password

encoding : An operation that maps something in the real world to a sequence of bits becomes encoded.

XOR: XOR operation, same as 0 xor, 0xor0=0,0xor1=1,1xor0=1,1xor1=0

the nature of the XOR : A xor or B XOR B is a.

One-time password book-the password that will never be deciphered

Definition: XOR the plaintext with a sequence of bits and the length of the plaintext.

does not have practicality.

DES (Data Encryption Standard)

Now des has been able to crack, the strength is not as good as before.

Specific operation:

Des is a symmetric cipher algorithm that encrypts 64 bits of plaintext into 64 bits of ciphertext, with a key length of 56 bits.

Des is encrypted in plaintext (bit sequence) of 64 bits, and this 64-bit unit becomes a grouping.

Feistel Network

Triple DES (Triple-des)

Triple DES is a cryptographic algorithm that is obtained to increase des strength by repeating des three times.

Triple DES has backward compatibility with Des.

Cryptography Beginner (i) basic concepts and DES encryption algorithm