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  man pages->Tru64 Unix man pages -> EVP_DigestInit (3)              



NAME    [Toc]    [Back]

       EVP_DigestInit,     EVP_DigestUpdate,     EVP_DigestFinal,
       EVP_MAX_MD_SIZE,       EVP_MD_CTX_copy,       EVP_MD_type,
       EVP_MD_pkey_type,      EVP_MD_size,     EVP_MD_block_size,
       EVP_MD_CTX_md,   EVP_MD_CTX_size,   EVP_MD_CTX_block_size,
       EVP_MD_CTX_type,  EVP_md_null,  EVP_md2, EVP_md5, EVP_sha,
       EVP_sha1,  EVP_dss,  EVP_dss1,  EVP_mdc2,   EVP_ripemd160,
       EVP_get_digestbyname, EVP_get_digestbynid, EVP_get_digestbyobj
 - EVP digest routines

SYNOPSIS    [Toc]    [Back]

       #include <openssl/evp.h>

       void EVP_DigestInit(
               EVP_MD_CTX  *ctx,  const  EVP_MD  *type  );   void
               EVP_MD_CTX  *ctx,  const void *d, unsigned int cnt
       ); void EVP_DigestFinal(
               EVP_MD_CTX    *ctx,     unsigned     char     *md,
       unsigned  int *s ); #define EVP_MAX_MD_SIZE (16+20) /* The
       SSLv3 md5+sha1 type */

       int EVP_MD_CTX_copy(
               EVP_MD_CTX   *out,EVP_MD_CTX   *in   );    #define
       EVP_MD_type(e)             ((e)->type)             #define
                        ((e)->pkey_type)                  #define
                          ((e)->md_size)                  #define
       EVP_MD_block_size(e)                           ((e)->block_size)

       #define                             EVP_MD_CTX_md(e)
                           (e)->digest)                   #define
              EVP_MD_size((e)->digest)                    #define
         EVP_MD_block_size((e)->digest)                   #define
       EVP_MD_CTX_type(e)                                  EVP_MD_type((e)->digest)

       EVP_MD *EVP_md_null(
               void ); EVP_MD *EVP_md2(
               void ); EVP_MD *EVP_md5(
               void ); EVP_MD *EVP_sha(
               void ); EVP_MD *EVP_sha1(
               void ); EVP_MD *EVP_dss(
               void ); EVP_MD *EVP_dss1(
               void ); EVP_MD *EVP_mdc2(
               void ); EVP_MD *EVP_ripemd160(
               void ); const EVP_MD *EVP_get_digestbyname(
               const char *name ); #define EVP_get_digestbynid(a)
       EVP_get_digestbyname(OBJ_nid2sn(a))                #define
       EVP_get_digestbyobj(a) EVP_get_digestbynid(OBJ_obj2nid(a))

DESCRIPTION    [Toc]    [Back]

       The EVP digest routines are a high level interface to message

       The EVP_DigestInit() function initializes a digest context
       ctx  to use a digest type. This will typically be supplied
       by a function such as EVP_sha1().

       The EVP_DigestUpdate() function hashes cnt bytes  of  data
       at  d  into  the  digest context ctx. This function can be
       called several times on the same ctx  to  hash  additional

       The  EVP_DigestFinal() function retrieves the digest value
       from ctx and places it in md.  If the s parameter  is  not
       NULL  then  the  number of bytes of data written (i.e. the
       length of the digest) will be written to the integer at s.
       At most EVP_MAX_MD_SIZE bytes will be written. After calling
 EVP_DigestFinal() no additional calls to EVP_DigestUpdate()
  can be made, but EVP_DigestInit() can be called to
       initialize a new digest operation.

       The EVP_MD_CTX_copy() function can be  used  to  copy  the
       message  digest  state  from in to out.  This is useful to
       hash large amounts of data which only differ in  the  last
       few bytes.

       The  EVP_MD_size()  and EVP_MD_CTX_size() functions return
       the size of the message digest when passed an EVP_MD or an
       EVP_MD_CTX structure, i.e. the size of the hash.

       The  EVP_MD_block_size() and EVP_MD_CTX_block_size() functions
 return the block size of  the  message  digest  when
       passed an EVP_MD or an EVP_MD_CTX structure.

       The  EVP_MD_type()  and EVP_MD_CTX_type() functions return
       the NID of the OBJECT IDENTIFIER  representing  the  given
       message  digest when passed an EVP_MD structure. For example,
 EVP_MD_type(EVP_sha1()) returns NID_sha1. This  function
 is normally used when setting ASN1 OIDs.

       The  EVP_MD_CTX_md() function returns the EVP_MD structure
       corresponding to the passed EVP_MD_CTX.

       The EVP_MD_pkey_type() function returns  the  NID  of  the
       public  key signing algorithm associated with this digest.
       For example, EVP_sha1() is associated  with  RSA  so  this
       will return NID_sha1WithRSAEncryption.

       The    EVP_md2(),    EVP_md5(),   EVP_sha(),   EVP_sha1(),
       EVP_mdc2(), and EVP_ripemd160()  functions  return  EVP_MD
       structures for the MD2, MD5, SHA, SHA1, MDC2 and RIPEMD160
       digest algorithms respectively. The  associated  signature
       algorithm is RSA in each case.

       The  EVP_dss()  and  EVP_dss1()  functions  return  EVP_MD
       structures for SHA and SHA1 digest  algorithms  but  using
       DSS (DSA) for the signature algorithm.

       The  EVP_md_null()  function is a null message digest that
       does nothing. The hash it returns is of zero length.

       The  EVP_get_digestbyname(),  EVP_get_digestbynid(),   and
       EVP_get_digestbyobj() functions return an EVP_MD structure
       when passed a digest name, a digest NID or an  ASN1_OBJECT
       structure  respectively. The digest table must be initialized
 using, for  example,  OpenSSL_add_all_digests(),  for
       these functions to work.

NOTES    [Toc]    [Back]

       The  EVP interface to message digests should almost always
       be used in preference to the low level interfaces. This is
       because  the  code  then becomes transparent to the digest
       used and much more flexible.

       SHA1 is the digest of choice  for  new  applications.  The
       other digest algorithms are still in common use.

RESTRICTIONS    [Toc]    [Back]

       Several  of  the  functions do not return values. Although
       the internal digest operations will never fail some future
       hardware based operations might.

       The link between digests and signing algorithms results in
       a situation where the EVP_sha1()  function  must  be  used
       with  RSA,  and  the EVP_dss1() function must be used with
       DSS even though they are identical digests.

       The size of an EVP_MD_CTX structure is determined at  compile
 time. This results in code that must be recompiled if
       the size of EVP_MD_CTX increases.

RETURN VALUES    [Toc]    [Back]

       The EVP_DigestInit(), EVP_DigestUpdate(), and  EVP_DigestFinal()
 functions do not return values.

       The  EVP_MD_CTX_copy() function returns 1 if successful or
       0 for failure.

       The EVP_MD_type(), EVP_MD_pkey_type(),  and  EVP_MD_type()
       functions return the NID of the corresponding OBJECT IDENTIFIER
 or NID_undef if none exists.

       The EVP_MD_size(), EVP_MD_block_size(), EVP_MD_CTX_size(),
       EVP_MD_size(),         EVP_MD_CTX_block_size(),        and
       EVP_MD_block_size() functions return the digest  or  block
       size in bytes.

       The   EVP_md_null(),   EVP_md2(),   EVP_md5(),  EVP_sha(),
       EVP_sha1(),   EVP_dss(),   EVP_dss1(),   EVP_mdc2(),   and
       EVP_ripemd160()  functions  return  pointers to the corresponding
 EVP_MD structures.

       The  EVP_get_digestbyname(),  EVP_get_digestbynid(),   and
       EVP_get_digestbyobj()  functions  return  either an EVP_MD
       structure or NULL if an error occurs.

EXAMPLE    [Toc]    [Back]

       The following example digests the  data  "Test  Message\n"
       and  "Hello  World\n", using the digest name passed on the
       command line:
        #include <stdio.h>
        #include <openssl/evp.h>

        main(int argc, char *argv[])
        EVP_MD_CTX mdctx;
        const EVP_MD *md;
        char mess1[] = "Test Message\n";
        char mess2[] = "Hello World\n";
        unsigned char md_value[EVP_MAX_MD_SIZE];
        int md_len, i;


        if(!argv[1]) {
            printf("Usage: mdtest digestname\n");      exit (1);

        md = EVP_get_digestbyname(argv[1]);

        if(!md) {
            printf("Unknown message digest %s\n", argv[1]);
         exit (1);

        EVP_DigestInit(&mdctx, md);
        EVP_DigestUpdate(&mdctx, mess1, strlen(mess1));
        EVP_DigestUpdate(&mdctx, mess2, strlen(mess2));
        EVP_DigestFinal(&mdctx, md_value, &md_len);

        printf("Digest is: ");
        for(i = 0; i < md_len; i++) printf("%02x", md_value[i]);

HISTORY    [Toc]    [Back]

       EVP_DigestInit(),  EVP_DigestUpdate(),  and  EVP_DigestFinal()
 are available in all versions of SSLeay and OpenSSL.

SEE ALSO    [Toc]    [Back]

       Commands: dgst(1)

       Functions:  evp(3),  hmac(3),  md2(3),  md5(3),   mdc2(3),
       ripemd(3), sha(3),

[ Back ]
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