MirBSD manpage: sha2(3), SHA256_Data(3), SHA256_End(3), SHA256_File(3), SHA256_FileChunk(3), SHA256_Final(3), SHA256_Init(3), SHA256_Pad(3), SHA256_Update(3), SHA384_Data(3), SHA384_End(3), SHA384_File(3), SHA384_FileChunk(3), SHA384_Final(3), SHA384_Init(3), SHA384_Pad(3), SHA384_Update(3), SHA512_Data(3), SHA512_End(3), SHA512_File(3), SHA512_FileChunk(3), SHA512_Final(3), SHA512_Init(3), SHA512_Pad(3), SHA512_Update(3)

SHA2(3)                    BSD Programmer's 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)


     #include <sys/types.h>
     #include <sha2.h>

     SHA256_Init(SHA256_CTX *context);

     SHA256_Update(SHA256_CTX *context, const void *data, size_t len);

     SHA256_Pad(SHA256_CTX *context);

     SHA256_Final(unsigned char digest[SHA256_DIGEST_LENGTH],
             SHA256_CTX *context);

     SHA256_Transform(u_int32_t state[8],
             const unsigned char 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(u_int8_t *data, size_t len, char *buf);

     SHA384_Init(SHA384_CTX *context);

     SHA384_Update(SHA384_CTX *context, const void *data, size_t len);

     SHA384_Pad(SHA384_CTX *context);

     SHA384_Final(unsigned char digest[SHA384_DIGEST_LENGTH],
             SHA384_CTX *context);

     SHA384_Transform(u_int64_t state[8],
             const unsigned char 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(u_int8_t *data, size_t len, char *buf);

     SHA512_Init(SHA512_CTX *context);

     SHA512_Update(SHA512_CTX *context, const void *data, size_t len);

     SHA512_Pad(SHA512_CTX *context);

     SHA512_Final(unsigned char digest[SHA512_DIGEST_LENGTH],
             SHA512_CTX *context);

     SHA512_Transform(u_int64_t state[8],
             const unsigned char 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(u_int8_t *data, size_t len, char *buf);


     The SHA2 functions implement the NIST Secure Hash Standard, FIPS PUB 180-
     2. The SHA2 functions are used to generate a condensed representation of
     a message called a message digest, suitable for use as a digital signa-
     ture. There are three families of functions, with names corresponding to
     the number of bits in the resulting message digest. The 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 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 con-
     verts the digest into an ASCII representation of the digest in hexade-

     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 negative 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. SHA256_DIGEST_STRING_LENGTH,
     the function being used) or a NULL pointer. In the latter case, space
     will be dynamically allocated via malloc(3) and should be freed using
     free(3) when it is no longer needed.


     The following code fragment will calculate the SHA-256 digest for the
     string "abc", which is

           SHA256_CTX ctx;
           u_int8_t results[SHA256_DIGEST_LENGTH];
           char *buf;
           size_t n;

           buf = "abc";
           n = strlen(buf);
           SHA256_Update(&ctx, buf, n);
           SHA256_Final(results, &ctx);

           /* Print the digest as one long hex value */
           for (n = 0; n < SHA256_DIGEST_LENGTH; n++)
                   printf("%02x", results[n]);

     Alternately, the helper functions could be used in the following way:

           SHA256_CTX ctx;
           u_int8_t output[SHA256_DIGEST_STRING_LENGTH];
           char *buf = "abc";

           printf("0x%s\n", SHA256_Data(buf, strlen(buf), output));


     cksum(1), adler32(3), md4(3), md5(3), rmd160(3), sfv(3), sha1(3),
     suma(3), tiger(3), whirlpool(3)

     Secure Hash Standard, FIPS PUB 180-2.


     The SHA2 functions appeared in OpenBSD 3.4.


     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.


     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 swapping on
     little endian machines such as the i386, alpha, and vax.

MirBSD #10-current              July 18, 2015                                3

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