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EVP_DigestInit(3)			     OpenSSL				EVP_DigestInit(3)

       EVP_MD_CTX_init, EVP_MD_CTX_create, EVP_DigestInit_ex, EVP_DigestUpdate, EVP_DigestFi-
       nal_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

	#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)

	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))

       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 func-
       tion 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 writ-
       ten.  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 con-
       text 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 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 auto-
       matically 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

       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 respec-
       tively. The digest table must be initialized using, for example, OpenSSL_add_all_digests()
       for these functions to work.

       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.

       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 effi-
       ciently reuse a digest context instead of initializing and cleaning it up on each call and
       allow non default implementations of digests to be specified.

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

       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;


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

	md = EVP_get_digestbyname(argv[1]);

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

	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);

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

       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

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

       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

       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

0.9.7a					    2002-07-18				EVP_DigestInit(3)
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