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NAME

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

SYNOPSIS

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 SHA2-256 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 SHA2-256 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 SHA2-256 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.