EVP_DigestInit man page on DigitalUNIX

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EVP_DigestInit(3)					     EVP_DigestInit(3)

       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

       #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_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)

       The EVP digest routines are a high level interface to message digests.

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

       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 data.

       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_DigestUp‐
       date() 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 sign‐
       ing 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 asso‐
       ciated 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 algo‐

       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_digest‐
       byobj() 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.

       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.

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

       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

       The EVP_DigestInit(), EVP_DigestUpdate(), and  EVP_DigestFinal()	 func‐
       tions do not return values.

       The  EVP_MD_CTX_copy()  function returns 1 if successful or 0 for fail‐

       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() func‐
       tions 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_digest‐
       byobj() functions return either an EVP_MD structure or NULL if an error

       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]);

       EVP_DigestInit(),  EVP_DigestUpdate(), and EVP_DigestFinal() are avail‐
       able in all versions of SSLeay and OpenSSL.

       Commands: dgst(1)

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


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