EVP_DigestInit(3)		    OpenSSL		     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_DigestInit, EVP_DigestFinal, 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_sha224, EVP_sha256,
       EVP_sha384, EVP_sha512, 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, size_t 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 64     /* SHA512 */

	int EVP_MD_type(const EVP_MD *md);
	int EVP_MD_pkey_type(const EVP_MD *md);
	int EVP_MD_size(const EVP_MD *md);
	int EVP_MD_block_size(const EVP_MD *md);

	const EVP_MD *EVP_MD_CTX_md(const EVP_MD_CTX *ctx);
	#define EVP_MD_CTX_size(e)	       EVP_MD_size(EVP_MD_CTX_md(e))
	#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_sha224(void);
	const EVP_MD *EVP_sha256(void);
	const EVP_MD *EVP_sha384(void);
	const EVP_MD *EVP_sha512(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 context ctx.

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

       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 function such 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 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
       context 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. Since digests and
       signature algorithms are no longer linked this function is only
       retained for compatibility reasons.

       EVP_md2(), EVP_md5(), EVP_sha(), EVP_sha1(), EVP_sha224(),
       EVP_sha256(), EVP_sha384(), EVP_sha512(), EVP_mdc2() and
       EVP_ripemd160() return EVP_MD structures for the MD2, MD5, SHA, SHA1,
       SHA224, SHA256, SHA384, SHA512, MDC2 and RIPEMD160 digest algorithms
       respectively.

       EVP_dss() and EVP_dss1() return EVP_MD structures for SHA and SHA1
       digest algorithms but using DSS (DSA) for the signature algorithm.
       Note: there is no need to use these pseudo-digests in OpenSSL 1.0.0 and
       later, they are however retained for compatibility.

       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_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() and
       EVP_MD_CTX_block_size() return the digest or block size in bytes.

       EVP_md_null(), EVP_md2(), EVP_md5(), EVP_sha(), EVP_sha1(),
       EVP_sha224(), EVP_sha256(), EVP_sha384(), EVP_sha512(), 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.

       New applications should use the SHA2 digest algorithms such as SHA256.
       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.

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

       Stack allocation of EVP_MD_CTX structures is common, for example:

	EVP_MD_CTX mctx;
	EVP_MD_CTX_init(&mctx);

       This will cause binary compatibility issues if the size of EVP_MD_CTX
       structure changes (this will only happen with a major release of
       OpenSSL).  Applications wishing to avoid this should use
       EVP_MD_CTX_create() instead:

	EVP_MD_CTX *mctx;
	mctx = EVP_MD_CTX_create();

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);
	}

	mdctx = EVP_MD_CTX_create();
	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_destroy(mdctx);

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

	/* Call this once before exit. */
	EVP_cleanup();
	exit(0);
	}

SEE ALSO
       dgst(1), evp(3)

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 truly
       const EVP_MD * in OpenSSL 0.9.7.

       The link between digests and signing algorithms was fixed in OpenSSL
       1.0 and later, so now EVP_sha1() can be used with RSA and DSA; there is
       no need to use EVP_dss1() any more.

       OpenSSL 1.0 and later does not include the MD2 digest algorithm in the
       default configuration due to its security weaknesses.



1.0.2k				  2023-11-15		     EVP_DigestInit(3)