Question

A financial services company still uses a legacy application that encrypts transaction records with Double DES (2DES), applying DES twice with two independent 56-bit keys, giving what management believes is 112 bits of effective security. A security architect reviewing the design warns that the actual effective key strength is far less than assumed. Which cryptanalytic attack is the architect most concerned about, and what is the resulting effective security?

Accepted Answer

A meet-in-the-middle attack, which reduces effective strength to roughly 57 bits, providing little more security than single DES

Answer

A birthday attack, which reduces effective strength to 56 bits by exploiting hash collisions in the ciphertext

Answer

A brute-force attack, which must still test the full 2^112 keyspace, so 2DES remains adequately secure

Answer

A related-key attack, which recovers both keys instantly because the two DES keys share a common schedule