SHASH(1)

NAME
shash - generates or checks digests or macs.

SYNOPSIS
shash [-qvmdbtlhVL ] [-c file] [-a algorithm] [-i config_file] [-o keymode] [-k key] [ filename ... ]

DESCRIPTION
Shash is a program intended to produce message digests for files, or it can check with the output of a former run whether the message digests are still the same (i.e. whether the files changed). This is like the way md5sum(1) and similar programs work. However this mode is insecure since anyone can recreate the digest, thus not suitable for security related applications. Because of this shash also supports HMAC (rfc2104), which is a mechanism for message authentication using cryptographic hash functions. So shash can use a key with a hash algorithm to produce hashes that can only be verified with the key. This way you can securely check (i.e. you are sure that nobody can modify the mac, without beeing detected) if files in a filesystem were altered. If the list of files and digests, that shash produces, is stored as a file in a disk, you should also create a digest of the list that holds the digests, to ensure that no file is removed from the list. If no filenames are given, it hashes the standard input to standard output.

OPTIONS

-m --hmac
    Works in hmac mode. Prompts for a password or accepts it from the --key parameter.

-h --help
    Display a help screen and quit.

-L --license
    Display the shash's license and quit.

-V --verbose
    Display some extra information.

--listkeygen
    Lists all the supported key generation algorithms. (The algorithms that generate a key from a password)

-o --keymode keymode
    Keymode may be one of the modes listed when the --listkeygen parameter is specified.

-q --quiet
    Suppress some not critical warnings.

-b  Use binary mode. In unix environment, only difference between this and the normal mode is an asterix preceding the filename in the output.

-c  Check the checksum of all files listed in file against the checksum listed in the same file.

-t, --text
    Treat all input files as text files. This is the reverse option to --binary.

-d, --doublecheck
    It prompts twice for the password.

--nosalt
    It does not use a salt, which is normally combined with the key in HMAC mode.

-k --key KEY
    Enter the keyword via the command line. The KEY is then used as keyword instead of prompting for it. Keep in mind that someone may see the command you are executing and so your key.

-c --config FILE
    Use the specified configuration file. The default is .shashrc in your home directory. The format of the configuration file is the same as the parameters. An example file is:
     algorithm sha1
     keymode s2k_simple
     key a_very_secret_one

-a --algorithm ALGORITHM
    The algorithm that will be used.

-l --list
    Displays the supported algorithms.

-v --version
    Version. Display the version number and quit.

ENVIRONMENT
Shash uses the following environment variables: SHASH_KEY: to specify the key. SHASH_KEYMODE; to specify the keymode. You can use these instead of using the command line (which is insecure).

SEE ALSO
md5sum(1)

DIAGNOSTICS
Exit status is normally 0;

Usage: shash [-qvmdbtlhVL] [-c file] [-a algorithm] [-i config_file] [-o keymode] [-k key] [filename...]

AUTHORS
Copyright (C) 1999,2002 Nikos Mavroyanopoulos (nmav@hellug.gr).