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 void
*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
void *data, unsigned int
len, char
*buf);
void
SHA1_Init
(SHA_CTX
*context);
void
SHA1_Update
(SHA_CTX
*context, const void
*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
void *data, unsigned int
len, char
*buf);
DESCRIPTION
TheSHA_
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 input.
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 It was quickly proven insecure, and has been superseded by SHA-1.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_Final
().
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 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 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.
SEE ALSO
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 instruction.)