.\" $FreeBSD: src/sbin/md5/md5.1,v 22.214.171.124 2001/12/14 15:17:49 ru Exp $ .Dd February 14, 1994 .Dt MD5 1 .Os .Sh NAME .Nm md5 .Nd calculate a message-digest fingerprint (checksum) for a file .Sh SYNOPSIS .Nm .Op Fl pqrtx .Op Fl s Ar string .Op Ar .Sh DESCRIPTION .Nm Md5 takes as input a message of arbitrary length and produces as output a 128-bit .Dq fingerprint or .Dq message digest of the input. It is conjectured that it is computationally infeasible to produce two messages having the same message digest, or to produce any message having a given prespecified target message digest. The MD5 algorithm is intended for digital signature applications, where a large file must be .Dq compressed in a secure manner before being encrypted with a private (secret) key under a public-key cryptosystem such as .Em RSA . .Pp MD5 has not yet (2001-09-03) been broken, but sufficient attacks have been made that its security is in some doubt. The attacks on MD5 are in the nature of finding .Dq collisions \(em that is, multiple inputs which hash to the same value; it is still unlikely for an attacker to be able to determine the exact original input given a hash value. .Pp The following options may be used in any combination and must precede any files named on the command line. The MD5 sum of each file listed on the command line is printed after the options are processed. .Bl -tag -width indent .It Fl s Ar string Print a checksum of the given .Ar string . .It Fl p Echo stdin to stdout and appends the MD5 sum to stdout. .It Fl q Quiet mode - only the MD5 sum is printed out. Overrides the .Fl r option. .It Fl r Reverses the format of the output. This helps with visual diffs. Does nothing when combined with the .Fl ptx options. .It Fl t Run a built-in time trial. .It Fl x Run a built-in test script. .El .Sh SEE ALSO .Xr cksum 1 .Rs .%A R. Rivest .%T The MD5 Message-Digest Algorithm .%O RFC1321 .Re .Sh ACKNOWLEDGMENTS This program is placed in the public domain for free general use by RSA Data Security.