SHA256(3) BSD Library Functions Manual SHA256(3)NAME
SHA256_Init, SHA256_Update, SHA256_Final, SHA256_End, SHA256_File,
SHA256_FileChunk, SHA256_Data — calculate the FIPS 180-2 ``SHA-256'' mes‐
SHA256_Update(SHA256_CTX *context, const unsigned char *data,
SHA256_Final(unsigned char digest, SHA256_CTX *context);
SHA256_End(SHA256_CTX *context, char *buf);
SHA256_File(const char *filename, char *buf);
SHA256_FileChunk(const char *filename, char *buf, off_t offset,
SHA256_Data(const unsigned char *data, unsigned int len, char *buf);
The SHA256_ functions calculate a 256-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
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().
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 speci‐
fied 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 argu‐
ment can be a null pointer, in which case the returned string is allo‐
cated 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.
SEE ALSOmd2(3), md4(3), md5(3), ripemd(3), sha(3)HISTORY
These functions appeared in FreeBSD 4.0.
The core hash routines were implemented by Colin Percival based on the
published FIPS 180-2 standard.
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.
BSD September 14, 2005 BSD