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SHA(3)			 BSD Library Functions Manual			SHA(3)

     SHA_Init, SHA_Update, SHA_Final, SHA_End, SHA_File, SHA_FileChunk,
     SHA_Data, SHA1_Init, SHA1_Update, SHA1_Final, SHA1_End, SHA1_File,
     SHA1_FileChunk, SHA1_Data -- calculate the	FIPS 160 and 160-1 ``SHA''
     message digests

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

     #include <sys/types.h>
     #include <sha.h>

     SHA_Init(SHA_CTX *context);

     SHA_Update(SHA_CTX	*context, const	unsigned char *data, size_t len);

     SHA_Final(unsigned	char digest[20], SHA_CTX *context);

     char *
     SHA_End(SHA_CTX *context, char *buf);

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

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

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

     SHA1_Init(SHA_CTX *context);

     SHA1_Update(SHA_CTX *context, const unsigned char *data, size_t len);

     SHA1_Final(unsigned char digest[20], SHA_CTX *context);

     char *
     SHA1_End(SHA_CTX *context,	char *buf);

     char *
     SHA1_File(const char *filename, char *buf);

     char *
     SHA1_FileChunk(const char *filename, char *buf, off_t offset,
	 off_t length);

     char *
     SHA1_Data(const unsigned char *data, unsigned int len, char *buf);

     The SHA_ and SHA1_	functions calculate a 160-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 in-

     SHA (or SHA-0) is the original Secure Hash	Algorithm specified in FIPS
     160.  It was quickly proven insecure, and has been	superseded by SHA-1.
     SHA-0 is included for compatibility purposes only.

     The SHA1_Init(), SHA1_Update(), and SHA1_Final() functions	are the	core
     functions.	 Allocate an SHA_CTX, initialize it with SHA1_Init(), run over
     the data with SHA1_Update(), and finally extract the result using

     SHA1_End()	is a wrapper for SHA1_Final() which converts the return	value
     to	a 41-character (including the terminating '\0')	ASCII string which
     represents	the 160	bits in	hexadecimal.

     SHA1_File() calculates the	digest of a file, and uses SHA1_End() to re-
     turn the result.  If the file cannot be opened, a null pointer is re-
     turned.  SHA1_FileChunk() is similar to SHA1_File(), but it only calcu-
     lates the digest over a byte-range	of the file specified, starting	at
     offset and	spanning length	bytes.	If the length parameter	is specified
     as	0, or more than	the length of the remaining part of the	file,
     SHA1_FileChunk() calculates the digest from offset	to the end of file.
     SHA1_Data() calculates the	digest of a chunk of data in memory, and uses
     SHA1_End()	to return the result.

     When using	SHA1_End(), SHA1_File(), or SHA1_Data(), the buf argument can
     be	a null pointer,	in which case the returned string is allocated 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 41
     characters	of buffer space.

     md2(3), md4(3), md5(3), ripemd(3),	sha256(3)

     These functions appeared in FreeBSD 4.0.

     The core hash routines were implemented by	Eric Young based on the	pub-
     lished FIPS standards.

     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.

     The IA32 (Intel) implementation of	SHA-1 makes heavy use of the `bswapl'
     instruction, which	is not present on the original 80386.  Attempts	to use
     SHA-1 on those processors will cause an illegal instruction trap.	(Ar-
     guably, the kernel	should simply emulate this instruction.)

BSD			       February	25, 1999			   BSD


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