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NAME

     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
      #include <openssl/evp.h>

      void EVP_DigestInit(EVP_MD_CTX *ctx, const EVP_MD *type);
      void EVP_DigestUpdate(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 EVP_MD_pkey_type(e)            ((e)->pkey_type)
      #define EVP_MD_size(e)                 ((e)->md_size)
      #define EVP_MD_block_size(e)           ((e)->block_size)

      #define EVP_MD_CTX_md(e)               (e)->digest)
      #define EVP_MD_CTX_size(e)             EVP_MD_size((e)->digest)
      #define EVP_MD_CTX_block_size(e)       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
     The EVP digest routines are a high level interface to
     message digests.


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

     EVP_DigestUpdate() 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 data.

     EVP_DigestFinal() 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.

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

     EVP_MD_size() and EVP_MD_CTX_size() 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.

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

     EVP_MD_type() and EVP_MD_CTX_type() 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.

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

     EVP_MD_pkey_type() 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. This "link" between digests and
     signature algorithms may not be retained in future versions
     of OpenSSL.

     EVP_md2(), EVP_md5(), EVP_sha(), EVP_sha1(), EVP_mdc2() and
     EVP_ripemd160() 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.

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

     EVP_md_null() is a "null" message digest that does nothing:
     i.e. the hash it returns is of zero length.

     EVP_get_digestbyname(), EVP_get_digestbynid() and
     EVP_get_digestbyobj() 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.



RETURN VALUES
     EVP_DigestInit(), EVP_DigestUpdate() and EVP_DigestFinal()
     do not return values.

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

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

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

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

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



NOTES
     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.



EXAMPLE
     This 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;

      OpenSSL_add_all_digests();

      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]);
      printf("\n");
      }




BUGS
     Several of the functions do not return values: maybe they
     should. 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 EVP_sha1() must be used with RSA and
     EVP_dss1() 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.



SEE ALSO
     evp(3), hmac(3), md2(3), md5(3), mdc2(3), ripemd(3), sha(3),
     digest(1)



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

     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"









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Created 1996-2024 by Maxim Chirkov

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