Idea behind internal SHA-2 functions

Asked Dec 31 '19 at 16:38

Active Jan 02 '20 at 00:05

Viewed 240 times

In the SHA-2 family, specifically SHA-256, there are functions called Sigma0 and Sigma1, which look like this:

Sigma0(b, c, d)
{
    Return (b & c) ^ (~b & d);
}

I don't really understand the logic or idea behind this. I looked on the internet a lot, but I couldn't find an answer to my question.

So does anybody know why they chose this specific function? Is it part of some secure block cipher or permutation algorithm? I couldn't find anything about the Ch and Maj online, nor what I'm asking now.

edited Jan 02 '20 at 00:05

Maarten Bodewes

92,551
13
161
313

asked Dec 31 '19 at 16:38

Ömer Enes Özmen

1

That is too deep. Check this question What makes SHA256 secure?. – kelalaka Dec 31 '19 at 16:53
Do you mean I have to find another place to ask? I don't really know any... – Ömer Enes Özmen Dec 31 '19 at 18:20
Not exactly, The functions are must be considered all together to achieve, the avalanche, confusion, and diffusion... – kelalaka Dec 31 '19 at 18:32
2

Analyze here – kelalaka Dec 31 '19 at 18:46
Thanks, so they are just build to be as random as possible and all of them together are "random enough", right? – Ömer Enes Özmen Jan 01 '20 at 09:27
True randomness is hard to achieve. What you have seen is the distribution is equal. This is necessary but not sufficient, the input bit may have a correlation with output bits that can be exploited, etc.. – kelalaka Jan 01 '20 at 09:31

Idea behind internal SHA-2 functions

0 Answers0