.\"-
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.\" Copyright (c) 2016 Dag-Erling Smørgrav
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.Dd September 17, 2016
.Dt CRYB_SHA256 3
.Os
.Sh NAME
.Nm cryb_sha256_init ,
.Nm cryb_sha256_update ,
.Nm cryb_sha256_final ,
.Nm cryb_sha256_complete
.Nd Secure Hash Algorithm 2
.Sh LIBRARY
.Lb libcryb-digest
.Sh SYNOPSIS
.In stddef.h
.In stdint.h
.In cryb/sha256.h
.Ft void
.Fn cryb_sha256_init "cryb_sha256_ctx *context"
.Ft void
.Fn cryb_sha256_update "cryb_sha256_ctx *context" "const void *data" "size_t len"
.Ft void
.Fn cryb_sha256_final "cryb_sha256_ctx *context" "uint8_t *digest"
.Ft void
.Fn cryb_sha256_complete "const void *data" "size_t len" "uint8_t *digest"
.Sh DESCRIPTION
The
.Nm cryb_sha256
family of functions implements the NIST SHA-256 message digest
algorithm as described in FIPS 180-4.
.Pp
The
.Fn cryb_sha256_init
function initializes the context structure pointed to by
.Va context .
It is the caller's responsibility to allocate this structure.
.Pp
The
.Fn cryb_sha256_update
function hashes the next
.Va len
bytes of data pointed to by the
.Va data
pointer into the given hash context.
.Pp
The
.Fn cryb_sha256_final
function finalizes the computation and writes the resulting message
digest to the caller-provided buffer pointed to by
.Va digest ,
which must be at least
.Dv SHA256_DIGEST_LEN
bytes long.
It is the caller's responsibility to dispose of the context structure
after calling
.Fn cryb_sha256_final .
.Pp
The
.Fn cryb_sha256_complete
function is a shortcut to calling
.Fn cryb_sha256_init ,
.Fn cryb_sha256_update
and
.Fn cryb_sha256_final
when the entire message is available up front in a single contiguous
buffer.
.Sh IMPLEMENTATION NOTES
The
.In cryb/sha256.h
header provides macros which allows these functions and the context
type to be referred to without their
.Dq Li cryb_
prefix.
.Sh SEE ALSO
.Xr cryb_digest 3 ,
.Xr cryb_sha1 3 ,
.Xr cryb_sha224 3 ,
.Xr cryb_sha384 3 ,
.Xr cryb_sha512 3
.Sh REFERENCES
.Rs
.%Q National Institute of Standards and Technology
.%R Secure Hash Standard (SHS) (FIPS PUB 180-4)
.%D March 2012
.Re
.Sh AUTHORS
These functions and this manual page were written for the University
of Oslo by
.An Dag-Erling Sm\(/orgrav Aq Mt d.e.smorgrav@usit.uio.no .