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Manual Pages  — MD5


md5, skein256 – calculate a message-digest fingerprint (checksum) for a file



md5 [-pqrtx] [-c string] [-s string] [file ...]

(All other hashes have the same options and usage.)


The md5 skein256, and skein1024 utilities take as input a message of arbitrary length and produce as output a "fingerprint" or "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 SHA-224, SHA-256, SHA-384, SHA-512, RIPEMD-160, and SKEIN algorithms are 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 MD5 and SHA-1 algorithms have been proven to be vulnerable to practical collision attacks and should not be relied upon to produce unique outputs, nor should they be used as part of a cryptographic signature scheme. As of 2017-03-02, there is no publicly known method to reverse either algorithm, i.e. to find an input that produces a specific output.

SHA-512t256 is a version of SHA-512 truncated to only 256 bits. On 64-bit hardware, this algorithm is approximately 50% faster than SHA-256 but with the same level of security. The hashes are not interchangeable.

It is recommended that all new applications use SHA-512 or SKEIN-512 instead of one of the other hash functions.

The following options may be used in any combination and must precede any files named on the command line. The hexadecimal checksum of each file listed on the command line is printed after the options are processed.
-c string
  Compare the digest of the file against this string. (Note that this option is not yet useful if multiple files are specified.)
-s string
  Print a checksum of the given string.
  Echo stdin to stdout and append the checksum to stdout.
  Quiet mode — only the checksum is printed out. Overrides the -r option.
  Reverses the format of the output. This helps with visual diffs. Does nothing when combined with the -ptx options.
  Run a built-in time trial.
  Run a built-in test script.


The md5, skein256 and skein1024 utilities exit 0 on success, 1 if at least one of the input files could not be read, and 2 if at least one file does not have the same hash as the -c option.


cksum(1), md5(3), ripemd(3), sha(3), sha224(3), sha256(3), sha384(3), sha512(3), skein(3)

R. Rivest, RFC1321, The MD5 Message-Digest Algorithm,

J. Burrows, FIPS PUB 180-2, The Secure Hash Standard,

D. Eastlake and P. Jones, RFC 3174, US Secure Hash Algorithm 1,

RIPEMD-160 is part of the ISO draft standard "ISO/IEC DIS 10118-3" on dedicated hash functions.

Secure Hash Standard (SHS): http://csrc.nist.gov/cryptval/shs.html.

The RIPEMD-160 page: http://www.esat.kuleuven.ac.be/~bosselae/ripemd160.html.


This program is placed in the public domain for free general use by RSA Data Security.

Support for SHA-1 and RIPEMD-160 has been added by Oliver Eikemeier <Mt eik@FreeBSD.org>.

MD5 (1) July 9, 2018

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