Losing the Code War by Stephen Budiansky

marius marius.corbu at analog.com
Fri Feb 1 17:41:52 EST 2002


"But there was an utterly trivial fix that DES users could employ if
they were worried
about security: they could simply encrypt each message twice, turning
56-bit DES into 112-bit DES, and squaring the number of key sequences
that
a code breaker would have to try. Messages could even be encrypted
thrice;
and, indeed, many financial institutions at the time were already using
"Triple DES." "

Not quite true. Encrypting each message twice would not increase the
"effective" key size to 112 bits.
There is an attack named "meet in the middle" which will make the
effective key size to be just 63 bits. This is why twice was not used
and they are using Triple DES, which has an effective key size of 112
bits.

Marius Corbu



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