SHA(3) BSD Library Functions Manual 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'' mes‐
SHA_Update(SHA_CTX *context, const unsigned char *data, size_t len);
SHA_Final(unsigned char digest, SHA_CTX *context);
SHA_End(SHA_CTX *context, char *buf);
SHA_File(const char *filename, char *buf);
SHA_FileChunk(const char *filename, char *buf, off_t offset,
SHA_Data(const unsigned char *data, unsigned int len, char *buf);
SHA1_Update(SHA_CTX *context, const unsigned char *data, size_t len);
SHA1_Final(unsigned char digest, SHA_CTX *context);
SHA1_End(SHA_CTX *context, char *buf);
SHA1_File(const char *filename, char *buf);
SHA1_FileChunk(const char *filename, char *buf, off_t offset,
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
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 It was quickly proven insecure, and has been superseded by SHA-1.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.
SEE ALSOmd2(3), md4(3), md5(3), ripemd(3), sha256(3)HISTORY
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.
(Arguably, the kernel should simply emulate this instruction.)
BSD February 25, 1999 BSD