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 conjectured 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 functions, such as
sha256(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 supported 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).
-sstring- Prints a checksum of the given string.
-t- Runs a built-in time trial. Specifying
-tmultiple times results in the number of rounds being multiplied by 10 for each additional 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.
EXIT STATUS
The md5 utility exits 0 on success,
and >0 if an error occurs.
SEE ALSO
STANDARDS
R. Rivest, The MD5 Message-Digest Algorithm, RFC 1321, April 1992.
CAVEATS
Since collisions have been found for MD5, the use of sha256(1) is recommended instead.