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SHA1_File (3)

>> SHA1_File (3) ( FreeBSD man: Библиотечные вызовы )

BSD mandoc

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'' message digests

LIBRARY

Lb libmd

SYNOPSIS

#include <sys/types.h>
#include <sha.h>
void SHA_Init (SHA_CTX *context);
void SHA_Update (SHA_CTX *context const unsigned char *data size_t len);
void SHA_Final (unsigned char digest[20] SHA_CTX *context);
char * SHA_End (SHA_CTX *context char *buf);
char * SHA_File (const char *filename char *buf);
char * SHA_FileChunk (const char *filename char *buf off_t offset off_t length);
char * SHA_Data (const unsigned char *data unsigned int len char *buf);
void SHA1_Init (SHA_CTX *context);
void SHA1_Update (SHA_CTX *context const unsigned char *data size_t len);
void SHA1_Final (unsigned char digest[20] SHA_CTX *context);
char * SHA1_End (SHA_CTX *context char *buf);
char * SHA1_File (const char *filename char *buf);
char * SHA1_FileChunk (const char *filename char *buf off_t offset off_t length);
char * SHA1_Data (const unsigned char *data unsigned int len char *buf);

DESCRIPTION

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 input.

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 It was quickly proven insecure, and has been superseded by SHA-1 SHA-0 is included for compatibility purposes only.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 Vt SHA_CTX , initialize it with SHA1_Init (,);
run over the data with SHA1_Update (,);
and finally extract the result using SHA1_Final (.);

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 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, SHA1_FileChunk ();
calculates the digest from Fa 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 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 41 characters of buffer space.

HISTORY

These functions appeared in Fx 4.0 .

AUTHORS

The core hash routines were implemented by Eric Young based on the published FIPS standards.

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.

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.)

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Created 1996-2024 by Maxim Chirkov
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