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+.\"
+.\" ----------------------------------------------------------------------------
+.\" "THE BEER-WARE LICENSE" (Revision 42):
+.\" <phk@FreeBSD.org> wrote this file.  As long as you retain this notice you
+.\" can do whatever you want with this stuff. If we meet some day, and you think
+.\" this stuff is worth it, you can buy me a beer in return.   Poul-Henning Kamp
+.\" ----------------------------------------------------------------------------
+.\"
+.\" 	From: Id: mdX.3,v 1.14 1999/02/11 20:31:49 wollman Exp
+.\" $FreeBSD$
+.\"
+.Dd April 1, 2011
+.Dt SHA512 3
+.Os
+.Sh NAME
+.Nm SHA512_Init ,
+.Nm SHA512_Update ,
+.Nm SHA512_Final ,
+.Nm SHA512_End ,
+.Nm SHA512_File ,
+.Nm SHA512_FileChunk ,
+.Nm SHA512_Data
+.Nd calculate the FIPS 180-2 ``SHA-512'' message digest
+.Sh LIBRARY
+.Lb libmd
+.Sh SYNOPSIS
+.In sys/types.h
+.In sha512.h
+.Ft void
+.Fn SHA512_Init "SHA512_CTX *context"
+.Ft void
+.Fn SHA512_Update "SHA512_CTX *context" "const unsigned char *data" "size_t len"
+.Ft void
+.Fn SHA512_Final "unsigned char digest[64]" "SHA512_CTX *context"
+.Ft "char *"
+.Fn SHA512_End "SHA512_CTX *context" "char *buf"
+.Ft "char *"
+.Fn SHA512_File "const char *filename" "char *buf"
+.Ft "char *"
+.Fn SHA512_FileChunk "const char *filename" "char *buf" "off_t offset" "off_t length"
+.Ft "char *"
+.Fn SHA512_Data "const unsigned char *data" "unsigned int len" "char *buf"
+.Sh DESCRIPTION
+The
+.Li SHA512_
+functions calculate a 512-bit cryptographic checksum (digest)
+for any number of input bytes.
+A cryptographic checksum is a one-way
+hash function; that is, it is computationally impractical to find
+the input corresponding to a particular output.
+This net result is
+a
+.Dq fingerprint
+of the input-data, which does not disclose the actual input.
+.Pp
+The
+.Fn SHA512_Init ,
+.Fn SHA512_Update ,
+and
+.Fn SHA512_Final
+functions are the core functions.
+Allocate an
+.Vt SHA512_CTX ,
+initialize it with
+.Fn SHA512_Init ,
+run over the data with
+.Fn SHA512_Update ,
+and finally extract the result using
+.Fn SHA512_Final .
+.Pp
+.Fn SHA512_End
+is a wrapper for
+.Fn SHA512_Final
+which converts the return value to a 65-character
+(including the terminating '\e0')
+.Tn ASCII
+string which represents the 512 bits in hexadecimal.
+.Pp
+.Fn SHA512_File
+calculates the digest of a file, and uses
+.Fn SHA512_End
+to return the result.
+If the file cannot be opened, a null pointer is returned.
+.Fn SHA512_FileChunk
+is similar to
+.Fn SHA512_File ,
+but it only calculates the digest over a byte-range of the file specified,
+starting at
+.Fa offset
+and spanning
+.Fa length
+bytes.
+If the
+.Fa length
+parameter is specified as 0, or more than the length of the remaining part
+of the file,
+.Fn SHA512_FileChunk
+calculates the digest from
+.Fa offset
+to the end of file.
+.Fn SHA512_Data
+calculates the digest of a chunk of data in memory, and uses
+.Fn SHA512_End
+to return the result.
+.Pp
+When using
+.Fn SHA512_End ,
+.Fn SHA512_File ,
+or
+.Fn SHA512_Data ,
+the
+.Fa buf
+argument can be a null pointer, in which case the returned string
+is allocated with
+.Xr malloc 3
+and subsequently must be explicitly deallocated using
+.Xr free 3
+after use.
+If the
+.Fa buf
+argument is non-null it must point to at least 65 characters of buffer space.
+.Sh SEE ALSO
+.Xr md2 3 ,
+.Xr md4 3 ,
+.Xr md5 3 ,
+.Xr ripemd 3 ,
+.Xr sha 3
+.Sh HISTORY
+These functions appeared in
+.Fx 4.0 .
+.Sh AUTHORS
+The core hash routines were implemented by Colin Percival based on
+the published
+.Tn FIPS 180-2
+standard.
+.Sh BUGS
+No method is known to exist which finds two files having the same hash value,
+nor to find a file with a specific hash value.
+There is on the other hand no guarantee that such a method does not exist.