Let's assume I've encrypted some text with some 24-byte key using 3DES in ECB mode. Is it possible to regain the key if I have both encrypted and decrypted text? (Excluding bruteforce.)
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2$\begingroup$ That would amount to divination. $\endgroup$– fgrieu ♦Commented Jan 22, 2014 at 9:17
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It is not practically possible. There are several attacks that are slightly faster than bruteforcing $2^{112}$ key candidates, but this is only a small factor. In some sense, they are bruteforce-like, since they require $2^{113}$ smaller steps.
answered Jan 22, 2014 at 11:10
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$\begingroup$ There are $2^{168}$ possible keys for 24 byte 3DES. It is possible to attack such key with around $2^{112}$ steps, which saves time compares to brute forcing all the possible keys. (But it is still unpractical.) $\endgroup$– user4982Commented May 9, 2014 at 16:05