Why to use 3DES and Blowfish instead of AES

Question

Could someone explain a couple of scenarios where the system design can justify the use of an encryption solution, respectively, as 3DES and Blowfish?

Answer 1

I'll add a few, one related to the backwards compatability: if you have a hardware implementation that only does 3DES (many older smartcards) then 3DES could be preferred over AES. Hardware accelerators can be used for both speedups and security (side channel attacks, see below).

3DES implementations may be less vulnerable to side channel attacks (although it certainly is not immune from it). AES is harder to get right - as I've come to understand - because of it's internal design (table accesses). AES better algo, bigger blocksize or key size does not mean much when confronted with a good side channel attack.

3DES has a 8 byte blocksize compared with 16 bytes for AES which can lead to a bit more overhead when using it in block mode encryption. Of course, this one can be mitigated by using a stream mode cipher, and we're only talking about a few bytes for the last block. This is an extremely thin argument for this reason.

I'll be a bit shorter on Blowfish: variable key size and sometimes faster than AES, less likely to be implemented in hardware, but backwards compatibility may be reasons, and the 8 byte blocksize again.

None of the three reasons above is generally enough to choose 3DES or Blowfish over AES of course.

Answer 2

Just one: backward compatibility with existing data or services/API that requires them.

Otherwise keep it simple and just use AES :-)

Note that people often suggest that using older algorithms gets better performance (not a very good tradeoff IMHO) but that's generally not the case (you'll need to test it against the library you use) and AES ends up way faster (at least from 3DES).

Answer 3

what about replacing the key addition subroutine with 3DES so that each block of the four blocks of eight characters get encrypted and including Blowfish F() inside the DES function F() i.e before the 32 bits is returned by the DES F(), I am actually using this idea to create a number generator to try and crack the lottery and to date have won £106.40, would love to upload the code but there is no way to do it here anyway.