On the security of 2-key triple DES
It addresses security concerns for users of 2-key triple DES, showing it is not completely broken but has a slim safety margin, urging replacement with the 3-key variant.
This paper re-evaluates the security of 2-key triple DES, a widely used encryption technique, by generalizing a 1990 attack and providing enhancements that challenge the conservative estimate of 80 bits of security and the practice of regular key changes.
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.