sha256



SHA256(1)                  OpenBSD Reference Manual                  SHA256(1)


NAME

     sha256 - calculate a message-digest fingerprint (checksum) for a file


SYNOPSIS

     sha256 [-bpqrtx] [-c [checklist ...]] [-s string] [file ...]


DESCRIPTION

     sha256 takes as input a message of arbitrary length and produces as
     output a 256-bit "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-256 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 SHA-256 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
             additional flag.

     -x      Runs a built-in test script.

     The SHA-256 sum of each file listed on the command line is printed after
     the options are processed.

     The sha256 command is shorthand for

           cksum -a sha256


EXIT STATUS

     The sha256 utility exits 0 on success, and >0 if an error occurs.


SEE ALSO

     cksum(1), md5(1), sha1(1)

     Secure Hash Standard, FIPS PUB 180-2.

OpenBSD 5.4                      July 8, 2012                      OpenBSD 5.4

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