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
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 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 It was quickly proven insecure, and has been superseded by SHA-1.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
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 instruction.)