It is well known (a little study on cryptography), DES is encrypted every 8 plaintext. . And DES has a good avalanche effect in every 8 expressions (it is a huge difference between ciphertext). But this also determined that the avalanche effect was not obvious when it was encrypted at the same time. Example of example:
Encrypted this paragraph with key infosecu: huazhong University is so good a university ranked 5th in China
The ciphertext drawn is:? K? -Mív? IA? B ¥ 6? Now, "Good" in the plain text is changed to "GEOD" ? K? -Mív? IA? B ¥ 6? Both compare "Good"? K? -Mív? ia? b ¥ 6? "goed"? K? -Mív? IA? b ¥ 6? It can be seen that most of the secrets have not changed, that is, the DES's avalanche effect only occurs in the 8-bit ciphertext in GoED, and is not strong. . The algorithm is now enhanced to have a good avalanche effect on the overall ciphertext. . The principle is as follows Taking the expressions of 64 characters as an example, the first DES encryption is performed every 8 groups, obtaining a total of 64-byte ciphertext in 8 groups, and the ciphertext is now packet Remove the first character of each group to re-constitute a group of 8 characters, then take out the second character of each group, the same constitutes a packet of 8 characters. In this way, we get a new 8-component group of ciphertext, while each group has a character from the original 8 packets. Then DES encryption is performed separately from the new 8 groups. That is to say, the change of the 1bit of the plaintext causes 8 byte changes in the original group, and the above-mentioned packet method is allocated to the change in the new 8 groups to the new 8 groups. The 64 characters generated after another DES encryption change (building an excellent avalanche effect based on DES pairs 8 characters). . Also use the previous example to explain the change effect "Good"? zí ?? ± f /? VCA? °? T?] é × _] ¢ S7G? V? ° o? §? ê? Y? w ¢ E? éfwo? ò? p "° § Q. "GoED" B? a? t2èê? pèr? 5? t? cbc [l? r ?? s' ÷ ?? 8 ???? ìt6 èE §v? ° WL ?? § ?? ^ It can be seen that only one character is changed, all 64 characters have changed, with the same method, we can extend the avalanche effect to more plain characters to produce a good avalanche effect.
