SHA 256 pseuedocode?

Question

I've been trying to work out how SHA-256 works. One thing I've been doing for other algorithms is I've worked out a sort of step by step pseudocode function for the algorithm.

I've tried to do the same for SHA256 but thus far I'm having quite a bit of trouble.

I've tried to work out how the Wikipedia diagram works but besides the text part explaining the functions I'm not sure I've got it right.

Here's what I have so far:

• Input is an array 8 items long where each item is 32 bits.
• Output is an array 8 items long where each item is 32 bits.
• Calculate all the function boxes and store those values. I'll refer to them by function name.
• Store input, right shifted by 32 bits, into output.
  • At this point, in the out array, E is the wrong value and A is empty
• Store the function boxes.
  • now we need to calculate out E and out A.
  • note: I've replaced the modulo commands with a bitwise AND 2^(32-1)

I can't figure out how the modulus adding lines up, but I think it is like this:

• Store (Input H + Ch + ( (Wt+Kt) AND 2^31 ) ) AND 2^31 As mod1
• Store (sum1 + mod1) AND 2^31 as mod2
• Store (d + mod2) AND 2^31 into output E
  • now output E is correct and all we need is output A
• Store (MA + mod2) AND 2^31 as mod3
• Store (sum0 + mod3) AND 2^31 into output A
  • output now contains the correct hash of input.
  • Do we return now or does this need to be run repeatedly?

Did I get all of those addition modulos right?

what are Wt and Kt?

Would this get run once, and you're done or does it need to be run a certain number of times, with the output being re-used as input?

Here's the link by the way. http://en.wikipedia.org/wiki/SHA-2#Hash_function

Thanks alot, Brian

Answer 1

Have a look at the official standard that describes the algorithm, the variables are described here: http://csrc.nist.gov/publications/fips/fips180-4/fips-180-4.pdf

(Oh, now I see I'm almost a year late with my answer, ah, never mind...)