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sha256_file(3) [freebsd man page]

SHA256(3)						   BSD 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'' mes- sage digest LIBRARY
Message Digest (MD4, MD5, etc.) Support Library (libmd, -lmd) 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 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 '') 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, start- ing 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 allo- cated 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. SEE ALSO
md4(3), md5(3), ripemd(3), sha(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. BSD
March 28, 2014 BSD

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SHA2(3) 						   BSD Library Functions Manual 						   SHA2(3)

SHA256_Init, SHA256_Update, SHA256_Pad, SHA256_Final, SHA256_Transform, SHA256_End, SHA256_File, SHA256_FileChunk, SHA256_Data -- calculate the NIST Secure Hash Standard (version 2) SYNOPSIS
#include <sys/types.h> #include <sha2.h> void SHA224_Init(SHA224_CTX *context); void SHA224_Update(SHA224_CTX *context, const uint8_t *data, size_t len); void SHA224_Pad(SHA224_CTX *context); void SHA224_Final(uint8_t digest[SHA224_DIGEST_LENGTH], SHA224_CTX *context); void SHA224_Transform(uint32_t state[8], const uint8_t buffer[SHA224_BLOCK_LENGTH]); 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(uint8_t *data, size_t len, char *buf); void SHA256_Init(SHA256_CTX *context); void SHA256_Update(SHA256_CTX *context, const uint8_t *data, size_t len); void SHA256_Pad(SHA256_CTX *context); void SHA256_Final(uint8_t digest[SHA256_DIGEST_LENGTH], SHA256_CTX *context); void SHA256_Transform(uint32_t state[8], const uint8_t buffer[SHA256_BLOCK_LENGTH]); 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(uint8_t *data, size_t len, char *buf); void SHA384_Init(SHA384_CTX *context); void SHA384_Update(SHA384_CTX *context, const uint8_t *data, size_t len); void SHA384_Pad(SHA384_CTX *context); void SHA384_Final(uint8_t digest[SHA384_DIGEST_LENGTH], SHA384_CTX *context); void SHA384_Transform(uint64_t state[8], const uint8_t buffer[SHA384_BLOCK_LENGTH]); char * SHA384_End(SHA384_CTX *context, char *buf); char * SHA384_File(char *filename, char *buf); char * SHA384_FileChunk(char *filename, char *buf, off_t offset, off_t length); char * SHA384_Data(uint8_t *data, size_t len, char *buf); void SHA512_Init(SHA512_CTX *context); void SHA512_Update(SHA512_CTX *context, const uint8_t *data, size_t len); void SHA512_Pad(SHA512_CTX *context); void SHA512_Final(uint8_t digest[SHA512_DIGEST_LENGTH], SHA512_CTX *context); void SHA512_Transform(uint64_t state[8], const uint8_t buffer[SHA512_BLOCK_LENGTH]); char * SHA512_End(SHA512_CTX *context, char *buf); char * SHA512_File(char *filename, char *buf); char * SHA512_FileChunk(char *filename, char *buf, off_t offset, off_t length); char * SHA512_Data(uint8_t *data, size_t len, char *buf); DESCRIPTION
The SHA2 functions implement the NIST Secure Hash Standard, FIPS PUB 180-2. The SHA2 functions are used to generate a condensed representa- tion of a message called a message digest, suitable for use as a digital signature. There are four families of functions, with names corre- sponding to the number of bits in the resulting message digest. The SHA-224 and SHA-256 functions are limited to processing a message of less than 2^64 bits as input. The SHA-384 and SHA-512 functions can process a message of at most 2^128 - 1 bits as input. The SHA2 functions are considered to be more secure than the sha1(3) functions with which they share a similar interface. The 224, 256, 384, and 512-bit versions of SHA2 share the same interface. For brevity, only the 256-bit variants are described below. The SHA256_Init() function initializes a SHA256_CTX context for use with SHA256_Update(), and SHA256_Final(). The SHA256_Update() function adds data of length len to the SHA256_CTX specified by context. SHA256_Final() is called when all data has been added via SHA256_Update() and stores a message digest in the digest parameter. The SHA256_Pad() function can be used to apply padding to the message digest as in SHA256_Final(), but the current context can still be used with SHA256_Update(). The SHA256_Transform() function is used by SHA256_Update() to hash 512-bit blocks and forms the core of the algorithm. Most programs should use the interface provided by SHA256_Init(), SHA256_Update(), and SHA256_Final() instead of calling SHA256_Transform() directly. The SHA256_End() function is a front end for SHA256_Final() which converts the digest into an ASCII representation of the digest in hexadeci- mal. The SHA256_File() function calculates the digest for a file and returns the result via SHA256_End(). If SHA256_File() is unable to open the file, a NULL pointer is returned. SHA256_FileChunk() behaves like SHA256_File() but calculates the digest only for that portion of the file starting at offset and continuing for length bytes or until end of file is reached, whichever comes first. A zero length can be specified to read until end of file. A nega- tive length or offset will be ignored. The SHA256_Data() function calculates the digest of an arbitrary string and returns the result via SHA256_End(). For each of the SHA256_End(), SHA256_File(), SHA256_FileChunk(), and SHA256_Data() functions the buf parameter should either be a string large enough to hold the resulting digest (e.g., SHA224_DIGEST_STRING_LENGTH, SHA256_DIGEST_STRING_LENGTH, SHA384_DIGEST_STRING_LENGTH, or SHA512_DIGEST_STRING_LENGTH, depending on the function being used) or a NULL pointer. In the latter case, space will be dynamically allo- cated via malloc(3) and should be freed using free(3) when it is no longer needed. EXAMPLES
The following code fragment will calculate the SHA-256 digest for the string "abc", which is ``0xba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad''. SHA256_CTX ctx; uint8_t results[SHA256_DIGEST_LENGTH]; char *buf; int n; buf = "abc"; n = strlen(buf); SHA256_Init(&ctx); SHA256_Update(&ctx, (uint8_t *)buf, n); SHA256_Final(results, &ctx); /* Print the digest as one long hex value */ printf("0x"); for (n = 0; n < SHA256_DIGEST_LENGTH; n++) printf("%02x", results[n]); putchar(' '); Alternately, the helper functions could be used in the following way: SHA256_CTX ctx; uint8_t output[SHA256_DIGEST_STRING_LENGTH]; char *buf = "abc"; printf("0x%s ", SHA256_Data(buf, strlen(buf), output)); SEE ALSO
cksum(1), md4(3), md5(3), rmd160(3), sha1(3) Secure Hash Standard, FIPS PUB 180-2. HISTORY
The SHA2 functions appeared in OpenBSD 3.4 and NetBSD 3.0. AUTHORS
This implementation of the SHA functions was written by Aaron D. Gifford. The SHA256_End(), SHA256_File(), SHA256_FileChunk(), and SHA256_Data() helper functions are derived from code written by Poul-Henning Kamp. CAVEATS
This implementation of the Secure Hash Standard has not been validated by NIST and as such is not in official compliance with the standard. If a message digest is to be copied to a multi-byte type (i.e.: an array of five 32-bit integers) it will be necessary to perform byte swap- ping on little endian machines such as the i386, alpha, and vax. BSD
May 20, 2009 BSD
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