On the security of 2-key triple DES

TL;DR

This paper analyzes the security of 2-key triple DES, revealing that its security margin is smaller than previously believed and highlighting the need for transitioning to more secure encryption methods.

Contribution

It introduces a generalized cryptanalysis attack on 2-key triple DES, improving upon previous methods and challenging assumptions about its security level.

Findings

The attack reduces the effective security of 2-key triple DES.

The scheme's security is less than the commonly estimated 80 bits.

Urgent replacement with 3-key triple DES or stronger schemes is recommended.

Abstract

This paper reconsiders the security offered by 2-key triple DES, an encryption technique that remains widely used despite recently being de-standardised by NIST. A generalisation of the 1990 van Oorschot-Wiener attack is described, constituting the first advance in cryptanalysis of 2-key triple DES since 1990. We give further attack enhancements that together imply that the widely used estimate that 2-key triple DES provides 80 bits of security can no longer be regarded as conservative; the widely stated assertion that the scheme is secure as long as the key is changed regularly is also challenged. The main conclusion is that, whilst not completely broken, the margin of safety for 2-key triple DES is slim, and efforts to replace it, at least with its 3-key variant, should be pursued with some urgency.