MD5(1)                     OpenBSD Reference Manual                     MD5(1)

NAME
     md5 - calculate a message-digest fingerprint (checksum) for a file

SYNOPSIS
     md5 [-bpqrtx] [-c [checklist ...]] [-s string] [file ...]

DESCRIPTION
     md5 takes as input a message of arbitrary length and produces as output a
     128-bit "fingerprint" or "message digest" of the input.  It was conjec-
     tured that it would be computationally infeasible to produce two messages
     having the same message digest (a collision), or to produce any message
     having a given prespecified target message digest.  However, collisions
     have now been produced for MD5, so the use of other message digest func-
     tions, such as sha1(1), is now preferred.

     The MD5 algorithm is intended for digital signature applications, where a
     large file must be "compressed" in a secure manner before being encrypted
     with a private (secret) key under a public-key cryptosystem such as RSA.

     The options are as follows:

     -b      Output checksums in base64 notation, not hexadecimal.

     -c [checklist ...]
             Compares all checksums contained in the file checklist with newly
             computed checksums for the corresponding files.  Output consists
             of the digest used, the file name, and an OK or FAILED for the
             result of the comparison.  This will validate any of the support-
             ed checksums (see cksum(1)).  If no file is given, stdin is used.

     -p      Echoes stdin to stdout and appends the MD5 sum to stdout.

     -q      Only print the checksum (quiet mode).

     -r      Reverse the format of the hash algorithm output, making it match
             the output format used by cksum(1).

     -s string
             Prints a checksum of the given string.

     -t      Runs a built-in time trial.  Specifying -t multiple times results
             in the number of rounds being multiplied by 10 for each addition-
             al flag.

     -x      Runs a built-in test script.

     The MD5 sum of each file listed on the command line is printed after the
     options are processed.

     The md5 utility exits 0 on success, and >0 if an error occurs.

SEE ALSO
     cksum(1), rmd160(1), sha1(1)

     R. Rivest, The MD5 Message-Digest Algorithm, RFC 1321.

CAVEATS
     Since collisions have been found for MD5, the use of sha1(1) is recom-
     mended instead.

OpenBSD 4.7                      May 31, 2007                                1
