SHA1-HASHCASH(1) sha1 SHA1-HASHCASH(1)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 func‐
tions 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 cor‐
responding 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 com‐
mand 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 preim‐
age:
"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 conven‐
tion 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>
SEE ALSOmd5sum(1), sha1(1), sha1sum(1), hashcash(1), http://www.hashcash.org/,
http://www.itl.nist.gov/fipspubs/fip180-1.htm
1.22 2006-04-07 SHA1-HASHCASH(1)
