# Why is the hashing (SHA256) specification symbol for rotate S and vice versa? [closed]

In the specification for SHA hashes, such as SHA-256, the symbol for a rotation is S and the symbol for a shift is R.

Is this an attempt to be deliberately confusing, or some kind of in joke, or what?

Here is the original document:

http://www.iwar.org.uk/comsec/resources/cipher/sha256-384-512.pdf

PS looks like they updated it in version 2 to use better abbreviations

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What specification are you referring to? Link? I just took a look at FIPS-180-4 which uses ROTL, ROTR for rotations and SHR, << and >> for shifts. –  CodesInChaos Oct 30 '13 at 16:10
We are not the authors of that document, Tyler, this question cannot be answered here - ask the authors. –  owlstead Oct 30 '13 at 16:26
FIPS-180-x is the official specification. No idea who wrote the document you link to. Perhaps it's a draft predating the final specification. –  CodesInChaos Oct 30 '13 at 16:26

## closed as primarily opinion-based by CodesInChaos, e-sushi, rath, fgrieu, AFSNov 1 '13 at 5:35

Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise.If this question can be reworded to fit the rules in the help center, please edit the question.

My guess is that $S$ comes from older SHA-1 specifications which also used it to mean "circular left Shift" (this can still be seen in RFC 3174: FIPS documents are revised, but RFC are eternal). SHA-1 uses only rotations, which it calls "circular shifts", so the use of $S$ seems logical. It was then imported in the to-become SHA-2, and the letter $R$ was used for a "Right shift" since the "S" was already used for the rotation.