Is there file format for checksums?

Question

I want to store SHA512 checksum of the file for my application. How to do it in common (popular) way? So this checksum can be used but by third party application too.

score 15 · Accepted Answer · answered Oct 21 '11 at 05:08

15

Write the checksum as lowercase hex digits followed by two spaces and then the filename, with one file per line. This is the format used by md5sum and the various sha*sum CLI tools.

$ sha512sum t.txt
d663b43c84ab4ba20040e568d3cb799512fcc00f1053f96f3079345f680b39429adc92f9c8c45fc9ae6053173ddc5b35ade25ae1d5c91e57b809d0c021d5c891  t.txt

$ sha512sum -c <(sha512sum t.txt)
t.txt: OK

answered Oct 21 '11 at 05:08

Ignacio Vazquez-Abrams

45,725

Does it support paths instead of filenames? – ShyBoy Oct 21 '11 at 07:44
1

It does, both relative and absolute. – Ignacio Vazquez-Abrams Oct 21 '11 at 10:45
3

@IgnacioVazquez-Abrams - Is there a standard maintained that dictates this file format? like ISO I always see checksum validators complaining about file format. WARNING: 20 lines are improperly formatted – sdc Sep 16 '16 at 06:30
@sdc: Not that I have seen. – Ignacio Vazquez-Abrams Sep 16 '16 at 07:21

score 7 · Answer 2 · edited Aug 03 '21 at 13:05

TL;DR

The file format is the output of the command you use to generate the digest.

$ shasum -a 512 [FILE] > SHA512SUM # create a checksum file (SHA512SUM)
$ shasum -c SHA512SUM              # verify [FILE] from checksum file
[FILE]: OK                         # output

See these other linux commands for simple ways to generating a checksum file

Long answer

It depends on which implementation of shasum you are using to check your checksum file.

If you are using a perl implementation ($ shasum -c [FILE]) then you can find the answer in the man pages. See $ man shasum

When checking, the input should be a former output of this program. The default mode is to print a line with checksum, a character indicating type ('*' for binary,' ' for text, '?' for portable, '^' for BITS), and name for each FILE.

If you are using a GNU implementation ($ sha512sum -c [FILE]) then the answer can be found under their coreutils documentation:

NOTE: The GNU sha digests documentation reference the md5sum digest documentation

For each file, ‘md5sum’ outputs by default, the MD5 checksum, a space, a flag indicating binary or text input mode, and the file name. Binary mode is indicated with ‘*’, text mode with ‘ ’ (space). Binary mode is the default on systems where it’s significant, otherwise text mode is the default. If file contains a backslash or newline, the line is started with a backslash, and each problematic character in the file name is escaped with a backslash, making the output unambiguous even in the presence of arbitrary file names. If file is omitted or specified as ‘-’, standard input is read.

Note the bit about the hash being possibly preceded by a forward slash. The newer doco allows for --zero which prevents the escaping and NUL termination. — Tom Hale, Sep 17 '19 at 08:06

score 4 · Answer 3 · answered Oct 21 '11 at 10:08

All schecksum files I've seen were just plain ASCII files which contained the checksum only. This way they may be easily compared with checksum command outputs.

Good practice is to indicate the checksum algorithm used with a filename suffix, eg .md5 or .crc.

Is there file format for checksums?

3 Answers3

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