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SHA256(3) FreeBSD Library Functions Manual SHA256(3)
NAME
SHA224_Init, SHA224_Update, SHA224_Final, SHA224_End, SHA224_File,
SHA224_FileChunk, SHA224_Data, SHA256_Init, SHA256_Update, SHA256_Final,
SHA256_End, SHA256_File, SHA256_FileChunk, SHA256_Data - calculate the
FIPS 180-2 ``SHA-256'' (or SHA-224) message digest
LIBRARY
Message Digest (MD4, MD5, etc.) Support Library (libmd, -lmd)
SYNOPSIS
#include <sys/types.h>
#include <sha224.h>
void
SHA224_Init(SHA224_CTX *context);
void
SHA224_Update(SHA224_CTX *context, const unsigned char *data,
size_t len);
void
SHA224_Final(unsigned char digest[32], SHA224_CTX *context);
char *
SHA224_End(SHA224_CTX *context, char *buf);
char *
SHA224_File(const char *filename, char *buf);
char *
SHA224_FileChunk(const char *filename, char *buf, off_t offset,
off_t length);
char *
SHA224_Data(const unsigned char *data, unsigned int len, char *buf);
#include <sha256.h>
void
SHA256_Init(SHA256_CTX *context);
void
SHA256_Update(SHA256_CTX *context, const unsigned char *data,
size_t len);
void
SHA256_Final(unsigned char digest[32], SHA256_CTX *context);
char *
SHA256_End(SHA256_CTX *context, char *buf);
char *
SHA256_File(const char *filename, char *buf);
char *
SHA256_FileChunk(const char *filename, char *buf, off_t offset,
off_t length);
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.
The SHA256_Init(), SHA256_Update(), and SHA256_Final() functions are the
core functions. Allocate an SHA256_CTX, initialize it with
SHA256_Init(), run over the data with SHA256_Update(), and finally
extract the result using SHA256_Final(), which will also erase the
SHA256_CTX.
SHA256_End() is a wrapper for SHA256_Final() which converts the return
value to a 65-character (including the terminating '\0') ASCII string
which represents the 256 bits in hexadecimal.
SHA256_File() calculates the digest of a file, and uses SHA256_End() to
return the result. If the file cannot be opened, a null pointer is
returned. SHA256_FileChunk() is similar to SHA256_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, SHA256_FileChunk() calculates the digest from offset to the end of
file. SHA256_Data() calculates the digest of a chunk of data in memory,
and uses SHA256_End() to return the result.
When using SHA256_End(), SHA256_File(), or SHA256_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 65 characters of buffer space.
SHA224 is identical SHA256, except it has slightly different
initialization vectors, and is truncated to a shorter digest.
ERRORS
The SHA256_End() function called with a null buf argument may fail and
return NULL if:
[ENOMEM] Insufficient storage space is available.
The SHA256_File() and SHA256_FileChunk() may return NULL when underlying
open(2), fstat(2), lseek(2), or SHA256_End(3) fail.
SEE ALSO
md4(3), md5(3), ripemd(3), sha(3), sha512(3), skein(3)
HISTORY
These functions appeared in FreeBSD 6.0.
AUTHORS
The core hash routines were implemented by Colin Percival based on the
published FIPS 180-2 standard.
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.
FreeBSD 14.0-RELEASE-p6 July 20, 2018 FreeBSD 14.0-RELEASE-p6