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

  • BSD mandoc
     

    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.  

    SEE ALSO

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

    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.


     

    Index

    NAME
    LIBRARY
    SYNOPSIS
    DESCRIPTION
    SEE ALSO
    HISTORY
    AUTHORS
    BUGS


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