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It's probably the generation of the IV that takes the time, not the 3DES encryption. 3DES encryption itself should indeed at least scale with the size of the plaintext.


One option is that your benchmarking code isn't exact enough to show the small differences. With long enough inputs the time should scale linearly with the number of 64-bit blocks. However, with small inputs, like your 1 vs. 125 blocks, it is possible to see the symptoms you describe – scaling decryption time, but approximately constant encryption time. You ...


This is both a DES (or any block cipher) and a programming concern. It is not a problem, just something to be aware of. The reason time/character decreases with larger plaintexts is that the initial overhead and memory management takes up the bulk of time with small inputs. With large inputs (megabytes+) the time/char will stabilize to a fairly consistent ...


Yes. The keys are indeed used in a linear manner. In particular, they are used in $E$-$D$-$E$ mode: encrypt using first 56 bits as key, decrypt using next 56 bits as key and then again encrypt using final 56 bits. This way its possible to use triple DES (which is officially called TDEA) for the DES, 2-DES and 3-DES variations. The first would use ...


This claim is bogus. DES itself has a 13-round differential with probability around $2^{-47}$, so TripleDES with its 48 rounds is resistant to any sort of differential attack. The paper authors are not really confident in the subject.

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