Can SHA1 , SHA-256 , SHA-512 be broken up to run across multiple cores/threads?

Question

I'm studying the speed (time to calculate hash) of SHA1 , SHA-256 , SHA-512 over different processors

Can these hashing algorithms be broken up to run across multiple cores/threads ?

Answer 1

If you're wondering about parallelizing the execution of computing a single hash (regardless of flavor 1, 256, or 512) then the answer is sadly no. That is because of the way the SHA transform function is defined. It operates on blocks of fixed size but the output of the transformation of each block is required by next so you can't run the computations in parallel.

Obviously it is possible to run multiple hashes in parallel, for different input strings, but that I assume you already knew.

If all you wanted was to generate digests for large inputs using underlying SHA transforms you could define an arbitrary scheme for segmenting the input and then generating digest blocks for each segment in parallel. Then combine those and so on..

Something like this:

 | ------------------ large input ---------------------------------------------|

 |    b0     |    b1    |    b2    |          |          |          |    bn    |

You can generate H(b0), H(b1), .. H(bn) in parallel.

Then, generate H_OUT = H(H(b0) + H(b1) + .. + H(bn)) (where the + sign could be concatenation or a simple XOR but these would very likely not be cryptographically strong).

This method will benefit from multiple cores but H_OUT will not be equivalent to computing a single hash of the original large input.