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Manual Reference Pages  - M_sha3 (3)

NAME
M_sha3(3fm) - [M_sha3] a module implementing the SHA-3 hash function

CONTENTS

Synopsis
Description
Example

SYNOPSIS
use M_sha3, only : sha3 use M_sha3, only : sha3_update use M_sha3, only : sha3_state use M_sha3, only : sha3_digest use M_sha3, only : sha3_hexdigest use M_sha3, only : sha3_file use M_sha3, only : sha3_auto_test

DESCRIPTION
This module implements the SHA-3 hash function, according to FIPS PUB 202, SHA-3 Standard: Permutation-Based Hash and Extendable-Output Functions, a NIST publication.

Originally based on routines from http://alcinoe.net/fortran.html

In this module, we focus on hashing strings of bytes (as opposed to strings of bits whose length is not a multiple of 8). We also focus on providing a fixed-length digest, rather than extendable output. For us, bytes mean integers of kind 1.

There are two ways of using the module:

o a functional form, in which the whole array of bytes to hash is passed to a function, which returns an array of bytes: 
          digest = sha3( buffer, d )
where d is an integer (default kind) that specifies the digest length in bits (so that ’digest’ should have a size of d/8)
o a subroutine form, which is typically used like this: 
           type(sha3_state) :: S
           call sha3_update( S, buffer1, d )
           call sha3_update( S, buffer2 )
           ...
           call sha3_digest( S, digest )
where you pass the data to hash little by little with
.sha3_update’, and finish the process with ’sha3_digest’ (after you which can start anew with the same state)

According to the standard, the digest size d may be one of 224, 256, 384, 512, which results in arrays of bytes of size 28, 32, 48 and
64. These arrays of bytes can be converted into a hexadecimal string of length 56, 64, 96 and 128 by calling the ’sha3_hexdigest’ function: 

        hd = sha3_hexdigest( digest )
If the data to hash is a string, one may convert it to an array of bytes or integer(kind=int8) using the transfer intrinsic: 

      buffer = transfer( string, buffer )
where size(buffer) = len(string)

The final routine exported by the module is sha3_auto_test(), which hashes some test vectors, as found on: 

      http://www.di-mgt.com.au/sha_testvectors.html
and some files in the directory ’test_vectors’, for which the digest was found using the Python implementation from 

      https://github.com/gvanas/KeccakCodePackage.

EXAMPLE
Sample program 

   program demo_M_sha3
   use M_sha3
   implicit none
   character(len=128) :: fname, arg
      call get_command_argument( 1, arg )
      if ( arg(1:1) .eq. ’-’ ) then
         if ( trim(arg) .eq. ’-a’ ) then
            call sha3_auto_test()
         else
            call get_command_argument( 2, fname )
           select case(trim(arg))
           case(’-224’); call sha3_file( 224, trim(fname) )
           case(’-256’); call sha3_file( 256, trim(fname) )
           case(’-384’); call sha3_file( 384, trim(fname) )
           case(’-512’); call sha3_file( 512, trim(fname) )
           case default
               print *,’usage: "sha3 -a" or "sha3 (-224|-256|-384|-512) fname"’
           end select
         endif
      else
         print *, ’usage: "sha3 -a" or "sha3 (-224|-256|-384|-512) fname"’
         print *, ’usage: "sha3 -a" or "sha3 (-224|-256|-384|-512) fname"’
      endif
end program demo_M_sha3

M_sha3 (3) March 11, 2021
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