[adrian_b]

Standard AES needs an 128-bit block.

However, the AES mixing function is made from a 32-bit mixing function that is extended to blocks whose lengths are multiples of 32-bit by composing it with a byte permutation.

The standard byte permutation extends the block size from 32-bit to 128-bit, but with the current AES instructions of CPUs you can either cancel the byte permutation to get a 32-bit block size or you can replace it with a non-standard byte permutation, to get any block size that is a multiple of 32-bit.

If you cancel the byte permutation, four 32-bit words are encrypted independently, instead of one 128-bit block. This doubles the number of instructions, but this does not necessarily reduce the throughput, as the instructions may be executed concurrently, so the throughput measured in encrypted numbers will increase by a number between 2 and 4, depending on the CPU.