sha(3)

NAME

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

LIBRARY

library ``libmd''

SYNOPSIS

#include <sys/types.h>
#include <sha.h>
void
SHA_Init(SHA_CTX *context);
void
SHA_Update(SHA_CTX  *context,  const  unsigned  char  *data,
size_t len);
void
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);
void
SHA1_Init(SHA_CTX *context);
void
SHA1_Update(SHA_CTX *context,  const  unsigned  char  *data,
size_t len);
void
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);

DESCRIPTION

The SHA_ and SHA1_ functions calculate a 160-bit crypto

graphic checksum
(digest) for any number of input bytes. A cryptographic

checksum is a
one-way hash function; that is, it is computationally im

practical 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.

SHA (or SHA-0) is the original Secure Hash Algorithm speci

fied in FIPS
160. It was quickly proven insecure, and has been super

seded 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

the data with SHA1_Update(), and finally extract the result

using
SHA1_Final().

SHA1_End() is a wrapper for SHA1_Final() which converts the

return value
to a 41-character (including the terminating ' ') ASCII

string which
represents the 160 bits in hexadecimal.

SHA1_File() calculates the digest of a file, and uses

SHA1_End

return the result. If the file cannot be opened, a null

pointer is
returned. SHA1_FileChunk() is similar to SHA1_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 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 mem

ory, 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 al

located 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.

SEE ALSO

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

HISTORY

These functions appeared in FreeBSD 4.0.

AUTHORS

The core hash routines were implemented by Eric Young based

on the published FIPS standards.

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.

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 instruc

tion.)

BSD February 25, 1999

BSD