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Re: triple DES


Hilarie Orman says:
> What is the usual method for doing triple DES with CBC?

Generally, an encrypt pass is followed by a decrypt pass and followed
by another encrypt pass. The three passes are run "independantly",
that is, as though a single plaintext was first encrypted in its
entirety in the first key, then decrypted with the second key, then
encrypted with the third -- phrased another way, the block chaining is
within each pass rather than between the passes.

If the first and second keys are set to be the same (or second and
third), this is equivalent to normal DES with the other key -- which
is useful in hardware 3DES implementations that need occassional
compatibility with DES.

Perry
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