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SHA256(3) FreeBSD Library Functions Manual SHA256(3) NAME SHA224_Init, SHA224_Update, SHA224_Final, SHA224_End, SHA224_File, SHA224_FileChunk, SHA224_Data, SHA256_Init, SHA256_Update, SHA256_Final, SHA256_End, SHA256_File, SHA256_FileChunk, SHA256_Data -- calculate the FIPS 180-2 ``SHA-256'' (or SHA-224) message digest LIBRARY Message Digest (MD4, MD5, etc.) Support Library (libmd, -lmd) SYNOPSIS #include <sys/types.h> #include <sha224.h> void SHA224_Init(SHA224_CTX *context); void SHA224_Update(SHA224_CTX *context, const unsigned char *data, size_t len); void SHA224_Final(unsigned char digest[32], SHA224_CTX *context); char * SHA224_End(SHA224_CTX *context, char *buf); char * SHA224_File(const char *filename, char *buf); char * SHA224_FileChunk(const char *filename, char *buf, off_t offset, off_t length); char * SHA224_Data(const unsigned char *data, unsigned int len, char *buf); #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 in- put corresponding to a particular output. This net result is a "fingerprint" of the input-data, which does not disclose the actual in- put. 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 ex- tract the result using SHA256_Final(), which will also erase the SHA256_CTX. 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 re- turned. SHA256_FileChunk() is similar to SHA256_File(), but it only cal- culates 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 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 us- ing free(3) after use. If the buf argument is non-null it must point to at least 65 characters of buffer space. SHA224 is identical SHA256, except it has slightly different initializa- tion vectors, and is truncated to a shorter digest. SEE ALSO md4(3), md5(3), ripemd(3), sha(3), sha512(3), skein(3) HISTORY These functions appeared in FreeBSD 6.0. 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. FreeBSD 13.0 July 20, 2018 FreeBSD 13.0
NAME | LIBRARY | SYNOPSIS | DESCRIPTION | SEE ALSO | HISTORY | AUTHORS | BUGS
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