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     /xlv3/openssl/0.9.7e-sgipl1/work/0.9.7e-sgipl1/openssl-
     0.9.7e/doc/crypto

     Page 1					    (printed 10/20/05)

     EVP_DigestInit(3)	   30/Sep/2003 (0.9.7e)	     EVP_DigestInit(3)

     NAME
	  EVP_MD_CTX_init, EVP_MD_CTX_create, EVP_DigestInit_ex,
	  EVP_DigestUpdate, EVP_DigestFinal_ex, EVP_MD_CTX_cleanup,
	  EVP_MD_CTX_destroy, EVP_MAX_MD_SIZE, EVP_MD_CTX_copy_ex,
	  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_MD_CTX_init(EVP_MD_CTX *ctx);
	   EVP_MD_CTX *EVP_MD_CTX_create(void);

	   int EVP_DigestInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
	   int EVP_DigestUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt);
	   int EVP_DigestFinal_ex(EVP_MD_CTX *ctx, unsigned char *md,
		  unsigned int *s);

	   int EVP_MD_CTX_cleanup(EVP_MD_CTX *ctx);
	   void EVP_MD_CTX_destroy(EVP_MD_CTX *ctx);

	   int EVP_MD_CTX_copy_ex(EVP_MD_CTX *out,const EVP_MD_CTX *in);

	   int EVP_DigestInit(EVP_MD_CTX *ctx, const EVP_MD *type);
	   int EVP_DigestFinal(EVP_MD_CTX *ctx, unsigned char *md,
		  unsigned int *s);

	   int EVP_MD_CTX_copy(EVP_MD_CTX *out,EVP_MD_CTX *in);

	   #define EVP_MAX_MD_SIZE (16+20) /* The SSLv3 md5+sha1 type */

	   #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)

     Page 1					    (printed 10/20/05)

     EVP_DigestInit(3)	   30/Sep/2003 (0.9.7e)	     EVP_DigestInit(3)

	   const EVP_MD *EVP_md_null(void);
	   const EVP_MD *EVP_md2(void);
	   const EVP_MD *EVP_md5(void);
	   const EVP_MD *EVP_sha(void);
	   const EVP_MD *EVP_sha1(void);
	   const EVP_MD *EVP_dss(void);
	   const EVP_MD *EVP_dss1(void);
	   const EVP_MD *EVP_mdc2(void);
	   const 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_MD_CTX_init() initializes digest contet ctx.

	  EVP_MD_CTX_create() allocates, initializes and returns a
	  digest contet.

	  EVP_DigestInit_ex() sets up digest context ctx to use a
	  digest type from ENGINE impl. ctx must be initialized before
	  calling this function. type will typically be supplied by a
	  functionsuch as EVP_sha1().  If impl is NULL then the
	  default implementation of digest type is used.

	  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_ex() 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_ex() no additional calls to
	  EVP_DigestUpdate() can be made, but EVP_DigestInit_ex() can
	  be called to initialize a new digest operation.

	  EVP_MD_CTX_cleanup() cleans up digest context ctx, it should
	  be called after a digest context is no longer needed.

	  EVP_MD_CTX_destroy() cleans up digest context ctx and frees
	  up the space allocated to it, it should be called only on a
	  context created using EVP_MD_CTX_create().

	  EVP_MD_CTX_copy_ex() can be used to copy the message digest
	  state from in to out. This is useful if large amounts of

     Page 2					    (printed 10/20/05)

     EVP_DigestInit(3)	   30/Sep/2003 (0.9.7e)	     EVP_DigestInit(3)

	  data are to be hashed which only differ in the last few
	  bytes. out must be initialized before calling this function.

	  EVP_DigestInit() behaves in the same way as
	  EVP_DigestInit_ex() except the passed context ctx does not
	  have to be initialized, and it always uses the default
	  digest implementation.

	  EVP_DigestFinal() is similar to EVP_DigestFinal_ex() except
	  the digest contet ctx is automatically cleaned up.

	  EVP_MD_CTX_copy() is similar to EVP_MD_CTX_copy_ex() except
	  the destination out does not have to be initialized.

	  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

     Page 3					    (printed 10/20/05)

     EVP_DigestInit(3)	   30/Sep/2003 (0.9.7e)	     EVP_DigestInit(3)

	  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_ex(), EVP_DigestUpdate() and
	  EVP_DigestFinal_ex() return 1 for success and 0 for failure.

	  EVP_MD_CTX_copy_ex() 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.

	  For most applications the impl parameter to
	  EVP_DigestInit_ex() will be set to NULL to use the default
	  digest implementation.

	  The functions EVP_DigestInit(), EVP_DigestFinal() and
	  EVP_MD_CTX_copy() are obsolete but are retained to maintain
	  compatibility with existing code. New applications should
	  use EVP_DigestInit_ex(), EVP_DigestFinal_ex() and
	  EVP_MD_CTX_copy_ex() because they can efficiently reuse a
	  digest context instead of initializing and cleaning it up on
	  each call and allow non default implementations of digests
	  to be specified.

     Page 4					    (printed 10/20/05)

     EVP_DigestInit(3)	   30/Sep/2003 (0.9.7e)	     EVP_DigestInit(3)

	  In OpenSSL 0.9.7 and later if digest contexts are not
	  cleaned up after use memory leaks will occur.

     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_MD_CTX_init(&mdctx);
	   EVP_DigestInit_ex(&mdctx, md, NULL);
	   EVP_DigestUpdate(&mdctx, mess1, strlen(mess1));
	   EVP_DigestUpdate(&mdctx, mess2, strlen(mess2));
	   EVP_DigestFinal_ex(&mdctx, md_value, &md_len);
	   EVP_MD_CTX_cleanup(&mdctx);

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

     BUGS
	  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.

     Page 5					    (printed 10/20/05)

     EVP_DigestInit(3)	   30/Sep/2003 (0.9.7e)	     EVP_DigestInit(3)

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

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

	  EVP_MD_CTX_init(), EVP_MD_CTX_create(),
	  EVP_MD_CTX_copy_ex(), EVP_MD_CTX_cleanup(),
	  EVP_MD_CTX_destroy(), EVP_DigestInit_ex() and
	  EVP_DigestFinal_ex() were added in OpenSSL 0.9.7.

	  EVP_md_null(), EVP_md2(), EVP_md5(), EVP_sha(), EVP_sha1(),
	  EVP_dss(), EVP_dss1(), EVP_mdc2() and EVP_ripemd160() were
	  changed to return truely const EVP_MD * in OpenSSL 0.9.7.

     Page 6					    (printed 10/20/05)

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