tags: cryptography
In the 2000s computation power started to increase, that lead to the possibility that DES could be broken by brute-force. Two new approaches were invented.
Double DES
A new approach was invented, and was that to use two DES Encryption blocks one after another with two different keys.
While it may seem that the current key space is , actually it can be broken in an easy way, using a Meet in the middle attack.
Given a known pair P and C, brute-force all the possibilities of K1 and add X to a table, after that sort the table, after that brute-force all the possibilities of K2 but instead decrypting C and for every X we get we do a look up in the table, if the text exists then we have found a possible key. The complexity of this attack is .
For a given Cipher-text we have possible keys, doing this again with the keys we got gives us possible keys, i.e. finding another match means it is mostly the correct key.
Triple DES
Another encryption algorithm was invented to fix the weakness of double DES and actually was the standard before the AES.
Triple DES is much harder to break, there is a proposed algorithm to break the triple DES in the reference page 197 which still has high complexity.
Doing MIM attack is useless here because for every plaintext P you will have to brute-force all possible ciphers A and save them in a table and do the same thing for the original cipher trying to get a B and after all that try to apply decryption to B by brute-forcing K2 and looking for a match with A. This is repeated for all possibilities of A.