Shulou(Shulou.com)06/01 Report--

In December 1980, FIPS 81 standardized four operating modes of DES: ECB, CBC, CFB and OFB. These working modes apply to any block cipher. As long as the packet length is changed from 64 bits to 128 bits, these modes can be applied to AES. Another mode of AES is the CTR mode. Let's introduce the pros and cons and uses of these patterns.

DES

DES is a 16-round Feistel type iterative cipher. The packet length 64bit, and the 64bit length is encrypted with the 56bit key.

AES

The packet length of AES is 128bit, and the three optional key lengths are 128 bits, 192 bits, and 256bit, with rounds of 10, 12 and 14, respectively.

Common working modes of No. 5 Middle School:

ECB (ElectronicCodebook, electronic code book):

Advantages: simple, parallel computing, no error transfer

Disadvantages: can not hide plaintext mode (for example, image encryption outline is still there), active * * (change plaintext, the subsequent content will not be affected, as long as the error does not transmit the defect)

Purpose: applications that require parallel encryption

CBC (Cipher Block Chaining, password grouping link):

Advantages: not easy to take the initiative (error transmission), suitable for long messages, is the SSL, IPSec standard

Disadvantages: non-parallelism, error transfer

Purpose: long message transmission, SSL and IPSec

CFB (CipherFeedback, password feedback):

Advantages: it is not easy to take the initiative (error transmission), the packet is converted to stream mode, and the encryption is less than grouped data.

Disadvantages: non-parallelism, error transfer

OFB (OutputFeedback, output feedback):

Advantages: packet switching to stream mode, encryption less than packet data

Disadvantages: active * (change the plaintext, the follow-up content will not be affected, as long as the error does not transmit the disadvantage)

Purpose: used when the quality of communication channel is not high, such as satellite communication

CTR (Counter, counter mode):

Description: calculator mode is not common, in CTR mode, there is a self-increasing operator, this operator uses the key to encrypt the output and the result of explicit XOR to get ciphertext, which is equivalent to one cipher at a time. This encryption method is simple, fast, secure and reliable, and can be encrypted in parallel, but when the calculator can not last very long, the key can only be used once.

Advantages: parallel, one at a time, no error transmission

Disadvantages: active * (change the plaintext, the follow-up content will not be affected, as long as the error does not transmit the disadvantage)

Summary

Grouping modes: ECB, CBC and CTR

Stream mode: CFB, OFB

Transfer error: CBC, CFB

Non-transmission error: ECB, OFB and CTR

Parallelizable: ECB, CTR

Not parallel: CBC, OFB, CFB

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