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SHA256_File (3)

>> SHA256_File (3) ( FreeBSD man: Библиотечные вызовы )

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NAME



SHA256_Init

 
SHA256_Update

 
SHA256_Final

 
SHA256_End

 
SHA256_File

 
SHA256_FileChunk

 
SHA256_Data

 - calculate the FIPS 180-2 ``SHA-256'' message digest

LIBRARY

Lb libmd

SYNOPSIS

#include <sys/types.h>
#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);
char * SHA256_Data (const unsigned char *data unsigned int len char *buf);

DESCRIPTION

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 input.

The SHA256_Init (,);
SHA256_Update (,);
and SHA256_Final ();
functions are the core functions. Allocate an Vt 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 Fa offset and spanning Fa length bytes. If the Fa length parameter is specified as 0, or more than the length of the remaining part of the file, SHA256_FileChunk ();
calculates the digest from Fa 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 Fa 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 Fa buf argument is non-null it must point to at least 65 characters of buffer space.

HISTORY

These functions appeared in Fx 4.0 .

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.

Партнёры:

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Created 1996-2024 by Maxim Chirkov
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