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SHA256(3)	       FreeBSD Library Functions Manual		     SHA256(3)

NAME
     SHA256_Init, SHA256_Update, SHA256_Final, SHA256_End, SHA256_File,
     SHA256_FileChunk, SHA256_Data -- calculate	the FIPS 180-2 ``SHA-256''
     message digest

LIBRARY
     Message Digest (MD4, MD5, etc.) Support Library (libmd, -lmd)

SYNOPSIS
     #include <sys/types.h>
     #include <sha256.h>

     void
     SHA256_Init(SHA256_CTX *context);

     void
     SHA256_Update(SHA256_CTX *context,	const unsigned char *data,
	 size_t	len);

     void
     SHA256_Final(unsigned char	digest[32], SHA256_CTX *context);

     char *
     SHA256_End(SHA256_CTX *context, char *buf);

     char *
     SHA256_File(const char *filename, char *buf);

     char *
     SHA256_FileChunk(const char *filename, char *buf, off_t offset,
	 off_t length);

     char *
     SHA256_Data(const unsigned	char *data, unsigned int len, char *buf);

DESCRIPTION
     The SHA256_ functions calculate a 256-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
     ``fingerprint'' of	the input-data,	which does not disclose	the actual
     input.

     The SHA256_Init(),	SHA256_Update(), and SHA256_Final() functions are the
     core functions.  Allocate an SHA256_CTX, initialize it with
     SHA256_Init(), run	over the data with SHA256_Update(), and	finally
     extract the result	using SHA256_Final().

     SHA256_End() is a wrapper for SHA256_Final() which	converts the return
     value to a	65-character (including	the terminating	'\0') ASCII string
     which represents the 256 bits in hexadecimal.

     SHA256_File() calculates the digest of a file, and	uses SHA256_End() to
     return the	result.	 If the	file cannot be opened, a null pointer is
     returned.	SHA256_FileChunk() is similar to SHA256_File(),	but it only
     calculates	the digest over	a byte-range of	the file specified, starting
     at	offset and spanning length bytes.  If the length parameter is speci-
     fied as 0,	or more	than the length	of the remaining part of the file,
     SHA256_FileChunk()	calculates the digest from offset to the end of	file.
     SHA256_Data() calculates the digest of a chunk of data in memory, and
     uses SHA256_End() to return the result.

     When using	SHA256_End(), SHA256_File(), or	SHA256_Data(), the buf argu-
     ment can be a null	pointer, in which case the returned string is allo-
     cated with	malloc(3) and subsequently must	be explicitly deallocated
     using free(3) after use.  If the buf argument is non-null it must point
     to	at least 65 characters of buffer space.

SEE ALSO
     md2(3), md4(3), md5(3), ripemd(3),	sha(3)

HISTORY
     These functions appeared in FreeBSD 6.0.

AUTHORS
     The core hash routines were implemented by	Colin Percival based on	the
     published FIPS 180-2 standard.

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.

FreeBSD	10.1		      September	14, 2005		  FreeBSD 10.1

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | SEE ALSO | HISTORY | AUTHORS | BUGS

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