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     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,
	 unsigned int 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,
	 unsigned int 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 *

     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  It was quickly proven insecure, and has been superseded by SHA-1.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
     return the result.  If the file cannot be opened, a null pointer is
     returned.	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)


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


     These functions appeared in FreeBSD 4.0.


     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 doesn't 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.
     (Arguably, the kernel should simply emulate this instruction.)

FreeBSD 5.4		       February 25, 1999		   FreeBSD 5.4


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