Extended des avalanche effect (original)

As we all know (a bit of research on cryptography), des is encrypted every 8-bit plaintext .. Des has a good avalanche effect in every 8-bit plaintext encryption (that is, changing the plaintext or key to 1 bit will cause a huge difference in the ciphertext ). However, this also determines that the avalanche effect of des on the simultaneous encryption of a large number of plain text is not obvious. Here is an example:

Encrypt the ciphertext with the key infosecu: Huazhong University is so good a university ranked 5th in China

The ciphertext obtained is :? K? -Mív? IA? B $6? <? DP protected WMD? PF? R | óq ?? ? Ya? ZJ? HP route 00006u then '? 81? +?

Change "good" to "geod" in plaintext to obtain the ciphertext.

? K? -Mív? IA? B $6? <? DP restart WQ ??.? Óq ?? ? Ya? ZJ? HP route 00006u then '? 81? +?

Comparison between the two

"Good "? K? -Mív? IA? B $6? <? DP protected WMD? PF? R | óq ?? ? Ya? ZJ? HP route 00006u then '? 81? +?

"Goed "? K? -Mív? IA? B $6? <? DP restart WQ ??.? Óq ?? ? Ya? ZJ? HP route 00006u then '? 81? +?

As you can see, the vast majority of ciphertext is not changed, that is, the avalanche effect of des only occurs in the eight-bit ciphertext where goed is located, and the avalanche effect on the overall ciphertext is not strong .. Now, the algorithm has a very good avalanche effect on the overall password .. The principle is as follows:

Take the 64-character plaintext as an example. Each group of 8 characters performs the first DES encryption to obtain 8 sets of 64-byte ciphertext. The ciphertext is grouped as follows:

The first character in each group is taken out to form an 8-character group, and the second character in each group is taken out to form an 8-character group.

In this way, we get the new eight groups of ciphertext, and each group has a character from the original eight groups. Then perform DES encryption on the new eight groups. That is to say, the change of 1 bit of plaintext leads to the change of 8 bytes in the original group, and the group method above distributes the change of 8 bytes to the change in the new 8 Group on average, as a result, all the 64 characters generated after the new eight groups are encrypted by DES (based on Des, which has an excellent avalanche effect on 8 characters ).. The same example is used to describe the change effect.

"Good "? Zsí ?? ± F /? VCA? °? T?] ? V? ° O? §? Why? Y? W ￠ e? É fwo? Why? P "? ° § Q.

"Goed" B? A? T2? P? 5? T? CBC [L? R ?? S 'records ?? 8 ???? O? T6 +? v? ° WL ?? §?? ^ U

We can see that only one character is changed, and the ciphertext of all 64 characters is changed. The same method is used, we can extend the avalanche effect to produce a good avalanche effect for more plaintext characters.