> ... could get the key within 3 weeks (3DES being ~3 times the work of single DES). Absolutely not! Trippling the key length does not just triple the strength

> ... could get the key within 3 weeks (3DES being ~3 times the work of single DES). Absolutely not! Trippling the key length does not just triple the strength... Against brute force every extra bit will force you to invest twice the time. Though 3DES only provides an effective security equivalent to 112 bits even with the strongest keying option due to an attack on it (instead of 168 bits). It's still probably infeasible to brute force currently: The factor between brute forcing DES and 3DES is about 2^56=7*10^16 (that's a big number!), not 3 as you seem to believe.