NAME

sha1 - Secure Hash Algorithm (version 1) hash function

SYNOPSIS

hash files:

sha1 [ files ]

DESCRIPTION

This is an implementation of the Secure Hash Algorithm version 1 as defined in US Federal Information Processing Standard "FIPS 180-1".

This was shipped for convenience with the hashcash tool, but also functions similarly to the widely distributed md5sum utility but using SHA1 instead of MD5 so you may find other uses for it. (Some have argued that MD5 is too small a hash to use for checking files if the attacker can insert chosen files into your distribution as then a birthday attack becomes possible for the master md5sum with work factor of about 2^64, which is a fairly high cost but not infeasible.)

OTHER IMPLEMENTATIONS

This program is fairly compatible with openssl sha1 (sha1(1)) and sha1sum (sha1sum(1)) installed on some unix systems and included with hashcash package so that a sha1 implementation is available for testing and scripting if those packages are missing.

USAGE NOTES

The sha1 program will hash the files given on the command line, or if no files are given it will hash the input fed to it on standard input. The output format is a list of SHA1 hashes in hex followed by the corresponding filenames, one per line.

EXAMPLES

Hashing files

"sha1 file1 file2 [...]": Hashes the files listed on the command line and outputs their SHA1 message digests as 40 hexadecimal digits, followed by the filename, one per line.
"echo -n abc ⎪ sha1": When no files are given, hashes from standard in. The example command hashes the string "abc" from standard input. This string is coincidentally one of the test vectors specified in FIPS 180-1 and should output: a9993e364706816aba3e25717850c26c9cd0d89d.
"echo -n abc ⎪ sha1 -": Equivalent to above. The filename of - means read from standard input.
"echo -n abc ⎪ sha1 test.txt -": You can also mix filenames and reading from standard input with the - pseudo file. The above command first hashes file "test.txt" then reads the string abc from standard in.

Verifying Hashcash

The SHA1 hash function is used by hashcash. You can use this sha1 utility to write shell scripts to verify hashcash tokens without using the hashcash command line tool, or just to verify visually. Say you received the following email:

 From: Someone <test@test.invalid>
 To: Adam Back <adam@cypherspace.org>
 Subject: test hashcash
 Date: Thu, 15 Aug 2002 11:12:02 +0000
 X-Hashcash: 0:030626:adam@cypherspace.org:6470e06d773e05a8

Then the following command would show visually the size of the preimage:

"echo -n 0:030626:adam@cypherspace.org:6470e06d773e05a8 ⎪ sha1"

 00000000c70db7389f241b8f441fcf068aead3f0

and you can see the leading hex 0s.

LIMITATIONS

Doesn't have the check option that md5sum has. Perhaps I'll add that in a future version. Also doesn't have the binary / text distinction that md5sum introduced for DOS/Windows benefit, nor the output convention signifying text (* after hash). Can't say I've ever seen anyone use that feature though.

EXIT STATUS

"sha1" returns success (exit code 0) normally.

If it can't read any of the files you give it on the comamnd line, it instead returns failure (exit code 1).

AUTHOR

Written by Adam Back <adam@cypherspace.org>