Intro To 'sha512sum' Command In Linux

2023-09-13 - By Robert Elder

     I use the 'sha512sum' command to compute the SHA 512 checksum of a file or stream:

sha512sum file1.txt

861844d6704e8573fec34d967e20bcfef3d424cf48be04e6dc08f2bd58c729743371015ead891cc3cf1c9d34b49264b510751b1ff9e537937bc46b5d6ff4ecc8  file1.txt

SHA 512 Versus SHA 256

     SHA 512 is extremely similar to SHA 256. The differences are mostly found in the block sizes:

Algorithm     Message Size (bits)    Block Size (bits)     Word Size (bits)     Message Digest Size (bits)
SHA-256       < 2^64                 512                   32                   256
SHA-512       < 2^128                1024                  64                   512

     Source: Figure 1 in Secure Hash Algorithm Properties, page 3 of fips180-3_final.pdf.

     Since the working variable size of SHA 512 is 64 bits instead of 32, many of the bit shift and rotation values are also different:

     In addition, the SHA 512 algorithm uses 80 calculation constants instead of the 64 that SHA 256 uses.  SHA 512 uses 80 rounds of computation instead of the 64 that SHA 256 uses.

     According to section 5.3.5 SHA-512 of fips180-3_final.pdf, the initial 8 hash values of SHA 512 come from "the first sixty-four bits of the fractional parts of the square roots of the first eight prime numbers." Some would argue that having a larger output bit size and using more computation rounds would make SHA 512 more secure than SHA 256.

Other Standard Features Of 'sha512sum' Command

     All of the SHA family checksums commands support the same flags and features, such as reading input from stdin:

echo "Hello World!" | sha512sum

830445e86a0cfafac4e1531002356f384847a11a7456fb8ccb81ab36e37bff28f34fa2c5bfdd347e964c5c5df0fc305de6394368219307b2ceeb0ec84b7c2b31  -

     or verifying checksums in the following file 'sha512-checksums.txt':

861844d6704e8573fec34d967e20bcfef3d424cf48be04e6dc08f2bd58c729743371015ead891cc3cf1c9d34b49264b510751b1ff9e537937bc46b5d6ff4ecc8  file1.txt
f7fbba6e0636f890e56fbbf3283e524c6fa3204ae298382d624741d0dc6638326e282c41be5e4254d8820772c5518a2c5a8c0c7f7eda19594a7eb539453e1ed7  file2.txt
8046964934182f830cc5286c28c13c697960b9d2b77620467a5039a2c3285ca4444cb05d1ee0641a54d664a75bca822aba52e0ca2e87bc86f1b013ba9e67c7e7  file3.txt

sha512sum -c sha512-checksums.txt

file1.txt: OK
file2.txt: OK
file3.txt: OK

     And that's why the 'sha512sum' command is my favourite Linux command.

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