Hacking Tutorial

Cryptanalytic Time-Memory Trade Off

Tutorial by LASEC
Cryptanalytic attacks based on exhaustive search need a lot of computing power
or a lot of time to complete. When the same attack has to be carried out multiple
times, it may be possible to execute the exhaustive search in advance and store
all results in memory. Once this precomputation is done, the attack can be
carried out almost instantly. Alas, this method is not practicable because of the
large amount of memory needed. In [4] Hellman introduced a method to trade
memory against attack time
. For a cryptosystem having N keys, this method
can recover a key in N 2/3 operations using N 2/3 words of memory. The typical
application of this method is the recovery of a key when the plaintext and the
ciphertext are known.

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