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SHA256(3)              FreeBSD Library Functions Manual              SHA256(3)

     SHA256_Init, SHA256_Update, SHA256_Final, SHA256_End, SHA256_File,
     SHA256_FileChunk, SHA256_Data - calculate the FIPS 180-2 ``SHA-256''
     message digest

     Message Digest (MD4, MD5, etc.) Support Library (libmd, -lmd)

     #include <sys/types.h>
     #include <sha256.h>

     SHA256_Init(SHA256_CTX *context);

     SHA256_Update(SHA256_CTX *context, const unsigned char *data,
         size_t len);

     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);

     char *
     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
     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.

     md2(3), md4(3), md5(3), ripemd(3), sha(3)

     These functions appeared in FreeBSD 6.0.

     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.

FreeBSD 11.0-PRERELEASE       September 14, 2005       FreeBSD 11.0-PRERELEASE


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