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7

DES is slow in software because it was designed back in the early 70's even before the 8086 processor existed, and uses several bit oriented operations that are just not implemented efficiently in a processor with a word oriented instruction set. Its intended product was ASIC hardware designs, in which DES runs quickly. DES hardware processors are quite ...


6

DES is slow compared to AES including in hardware because for comparable security we must use 3DES, which triples the number of rounds per block, to 48 for 3DES versus 10, 12, or 14 for AES; DES's block size is 64 bits, half of AES's 128 bit; so when encrypting a sizable block of data, 3DES does more rounds that AES by a factor of 96/10, 96/12, or 96/14; ...


3

You cannot encrypt 720 bits plaintext using just AES-128. AES is a 128 bit block cipher. Such a block cipher has an input of 128 bits of plaintext and an output of 128 bits ciphertext; and that's it. You need some kind of construction to make block ciphers encrypt larger or smaller plaintext. Such constructions are known as (block cipher) modes of ...


2

According to Wikipedia, GCM is defined for block ciphers with a block size of 128 bits. So no, you can't use GCM with 3DES or DES, because of the 64-bit block size. You could use something similar to GCM, but it wouldn't be GCM.


1

The speed of individual algorithms strongly depends on their implementation. This goes for both hashing algorithms as well as encryption algorithms. This quickly becomes clear if you take a look at efforts like “eBACS: ECRYPT Benchmarking of Cryptographic Systems” and the results presented. Also, you should not ignore that some algorithms have specifically ...


1

The meet-in-the-middle attack still applies; instead of attack effort 257 DES invocations, you just increased it by 256 extra DES block encryptions, i.e. up to about 257.6 in total: a mere +50% increase. On the other hand, you also made the overall block cipher (your two-key triple encryption) 50% more expensive to use, so the overall security has not ...



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