Manual Pages for UNIX Operating System command usage for man SHA256Init

Extended Library Functions                             sha2(3EXT)



NAME
     sha2,   SHA2Init,   SHA2Update,    SHA2Final,    SHA256Init,
     SHA256Update,    SHA256Final,    SHA384Init,   SHA384Update,
     SHA384Final, SHA512Init, SHA512Update,  SHA512Final  -  SHA2
     digest functions

SYNOPSIS
     cc [ flag ... ] file ... -lmd [ library ... ]
     #include 

     void SHA2Init(uint64_t mech, SHA2_CTX *context);


     void SHA2Update(SHA2_CTX *context, unsigned char *input,
          unsigned int inlen);


     void SHA2Final(unsigned char *output, SHA2_CTX *context);


     void SHA256Init(SHA256_CTX *context);


     void SHA256Update(SHA256_CTX *context, unsigned char *input,
          unsigned int inlen);


     void SHA256Final(unsigned char *output, SHA256_CTX *context);


     void SHA384Init(SHA384_CTX *context);


     void SHA384Update(SHA384_CTX *context, unsigned char *input,
          unsigned int inlen);


     void SHA384Final(unsigned char *output, 384_CTX *context);


     void SHA512Init(SHA512_CTX *context);


     void SHA512Update(SHA512_CTX *context, unsigned char *input,
          unsigned int inlen);


     void SHA512Final(unsigned char *output, 512_CTX *context);


DESCRIPTION




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Extended Library Functions                             sha2(3EXT)



     The SHA2Init(), SHA2Update(), SHA2Final()  functions  imple-
     ment  the  SHA256,  SHA384  and  SHA512 message-digest algo-
     rithms. The algorithms take as input a message of  arbitrary
     length and produces a 200-bit "fingerprint" or "message dig-
     est" as  output.  The  SHA2  message-digest  algorithms  are
     intended  for  digital signature applications in which large
     files are "compressed"  in  a  secure  manner  before  being
     encrypted  with  a  private  (secret) key under a public-key
     cryptosystem such as RSA.

     SHA2Init(), SHA2Update(), SHA2Final()

         The SHA2Init(), SHA2Update(), and SHA2Final()  functions
         allow  an  SHA2 digest to be computed over multiple mes-
         sage blocks. Between blocks, the state of the SHA2  com-
         putation  is held in an SHA2 context structure allocated
         by the caller. A complete digest computation consists of
         calls to SHA2 functions in the following order: one call
         to SHA2Init(), one or more calls  to  SHA2Update(),  and
         one call to SHA2Final().

         The SHA2Init() function  initializes  the  SHA2  context
         structure  pointed  to  by context. The mech argument is
         one of SHA256, SHA512, SHA384.

         The SHA2Update() function computes a partial SHA2 digest
         on the inlen-byte message block pointed to by input, and
         updates the SHA2 context structure pointed to by context
         accordingly.

         The SHA2Final() function generates the  final  SHA2Final
         digest,  using  the SHA2 context structure pointed to by
         context. The SHA2 digest is written to output.  After  a
         call  to SHA2Final(), the state of the context structure
         is undefined. It must be reinitialized  with  SHA2Init()
         before it can be used again.


     SHA256Init(), SHA256Update(), SHA256Final(), SHA384Init(),
     SHA384Update(), SHA384Final(), SHA512Init(), SHA512Update(),
     SHA512Final()

         Alternative APIs exist as named above. The Update()  and
         Final()  sets of functions operate exactly as the previ-
         ously described SHA2Update() and SHA2Final()  functions.
         The  SHA256Init(),  SHA384Init(), and SHA512Init() func-
         tions do not take the mech argument as it is implicit in
         the function names.


RETURN VALUES




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Extended Library Functions                             sha2(3EXT)



     These functions do not return a value.

EXAMPLES
     Example 1 Authenticate a message found in multiple buffers


     The following is a sample function that authenticates a mes-
     sage  found  in  multiple buffers. The calling function pro-
     vides an authentication buffer to contain the result of  the
     SHA2 digest.


       #include 
       #include 
       #include 

       int
       AuthenticateMsg(unsigned char *auth_buffer, struct iovec
                       *messageIov, unsigned int num_buffers)
       {
           SHA2_CTX sha2_context;
           unsigned int i;

           SHA2Init(SHA384, &sha2_context);

           for(i=0; i           {
                SHA2Update(&sha2_context, messageIov->iov_base,
                          messageIov->iov_len);
                messageIov += sizeof(struct iovec);
           }

           SHA2Final(auth_buffer, &sha2_context);

           return 0;
       }


     Example 2 Authenticate a message found in multiple buffers


     The following is a sample function that authenticates a mes-
     sage  found  in  multiple buffers. The calling function pro-
     vides an authentication buffer that will contain the  result
     of the SHA384 digest, using alternative interfaces.


       int
       AuthenticateMsg(unsigned char *auth_buffer, struct iovec
                       *messageIov, unsigned int num_buffers)
       {
           SHA384_CTX ctx;



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Extended Library Functions                             sha2(3EXT)



           unsigned int i;

           SHA384Init(&ctx);

           for(i=0, i           {
                SHA384Update(&ctx, messageIov->iov_base,
                          messageIov->iov_len);
                messageIov += sizeof(struct iovec);
           }

           SHA384Final(auth_buffer, &ctx);

           return 0;
       }


ATTRIBUTES
     See attributes(5) for descriptions of the  following  attri-
     butes:



     ____________________________________________________________
    |       ATTRIBUTE TYPE        |       ATTRIBUTE VALUE       |
    |_____________________________|_____________________________|
    | Interface Stability         | Committed                   |
    |_____________________________|_____________________________|
    | MT-Level                    | MT-Safe                     |
    |_____________________________|_____________________________|


SEE ALSO
     libmd(3LIB)


     FIPS 180-2


















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