meet-in-the-middle attack

Summary

Space-time tradeoff

• using more space to save time
• ie. lookup tables

Triple encryption

• double the security
• only need 2 keys since the man-in-the-middle attack renders the 3rd useless

3DES

• encryptions/decryptions

Concept

Double encryption

Normal exhaustive search(known plaintext attack)

• do the two levels of encryption for every possible key

Meet-in-the-middle(known plaintext attack)

• do one encryption and one decryption
• find the matching intermediate

the forward encryptions can be stored in a hash table to be checked against the backward decryptions

Application

4DES

not much better than 3DES, a good stream cipher is a better option