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EVP_DIGESTINIT(3)		    OpenSSL		     EVP_DIGESTINIT(3)

NAME
       EVP_MD_CTX_new, EVP_MD_CTX_reset, EVP_MD_CTX_free, EVP_MD_CTX_copy_ex,
       EVP_MD_CTX_ctrl,	EVP_MD_CTX_set_flags, EVP_MD_CTX_clear_flags,
       EVP_MD_CTX_test_flags, EVP_DigestInit_ex, EVP_DigestInit,
       EVP_DigestUpdate, EVP_DigestFinal_ex, EVP_DigestFinalXOF,
       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_CTX_md_data,
       EVP_md_null, EVP_get_digestbyname, EVP_get_digestbynid,
       EVP_get_digestbyobj, EVP_MD_CTX_set_pkey_ctx - EVP digest routines

SYNOPSIS
	#include <openssl/evp.h>

	EVP_MD_CTX *EVP_MD_CTX_new(void);
	int EVP_MD_CTX_reset(EVP_MD_CTX	*ctx);
	void EVP_MD_CTX_free(EVP_MD_CTX	*ctx);
	void EVP_MD_CTX_ctrl(EVP_MD_CTX	*ctx, int cmd, int p1, void* p2);
	void EVP_MD_CTX_set_flags(EVP_MD_CTX *ctx, int flags);
	void EVP_MD_CTX_clear_flags(EVP_MD_CTX *ctx, int flags);
	int EVP_MD_CTX_test_flags(const	EVP_MD_CTX *ctx, int flags);

	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_DigestFinalXOF(EVP_MD_CTX *ctx,	unsigned char *md, size_t len);

	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);

	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);
	int EVP_MD_CTX_size(const EVP_MD *ctx);
	int EVP_MD_CTX_block_size(const	EVP_MD *ctx);
	int EVP_MD_CTX_type(const EVP_MD *ctx);
	void *EVP_MD_CTX_md_data(const EVP_MD_CTX *ctx);

	const EVP_MD *EVP_md_null(void);

	const EVP_MD *EVP_get_digestbyname(const char *name);
	const EVP_MD *EVP_get_digestbynid(int type);
	const EVP_MD *EVP_get_digestbyobj(const	ASN1_OBJECT *o);

	void EVP_MD_CTX_set_pkey_ctx(EVP_MD_CTX	*ctx, EVP_PKEY_CTX *pctx);

DESCRIPTION
       The EVP digest routines are a high level	interface to message digests,
       and should be used instead of the cipher-specific functions.

       EVP_MD_CTX_new()
	   Allocates and returns a digest context.

       EVP_MD_CTX_reset()
	   Resets the digest context ctx.  This	can be used to reuse an
	   already existing context.

       EVP_MD_CTX_free()
	   Cleans up digest context ctx	and frees up the space allocated to
	   it.

       EVP_MD_CTX_ctrl()
	   Performs digest-specific control actions on context ctx.

       EVP_MD_CTX_set_flags(), EVP_MD_CTX_clear_flags(),
       EVP_MD_CTX_test_flags()
	   Sets, clears	and tests ctx flags.  See "FLAGS" below	for more
	   information.

       EVP_DigestInit_ex()
	   Sets	up digest context ctx to use a digest type from	ENGINE impl.
	   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_DigestFinalXOF()
	   Interfaces to extendable-output functions, XOFs, such as SHAKE128
	   and SHAKE256.  It retrieves the digest value	from ctx and places it
	   in len-sized	<B>md.	After calling this function no additional
	   calls to EVP_DigestUpdate() can be made, but	EVP_DigestInit_ex()
	   can be called to initialize a new operation.

       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.

       EVP_DigestInit()
	   Behaves in the same way as EVP_DigestInit_ex() except it always
	   uses	the default digest implementation.

       EVP_DigestFinal()
	   Similar to EVP_DigestFinal_ex() except the digest context ctx is
	   automatically cleaned up.

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

       EVP_MD_size(), 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(), 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(), 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_data()
	   Return the digest method private data for the passed	EVP_MD_CTX.
	   The space is	allocated by OpenSSL and has the size originally set
	   with	EVP_MD_meth_set_app_datasize().

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

       EVP_get_digestbyname(), EVP_get_digestbynid(), EVP_get_digestbyobj()
	   Returns an EVP_MD structure when passed a digest name, a digest NID
	   or an ASN1_OBJECT structure respectively.

       EVP_MD_CTX_set_pkey_ctx()
	   Assigns an EVP_PKEY_CTX to EVP_MD_CTX. This is usually used to
	   provide a customzied	EVP_PKEY_CTX to	EVP_DigestSignInit(3) or
	   EVP_DigestVerifyInit(3). The	pctx passed to this function should be
	   freed by the	caller.	A NULL pctx pointer is also allowed to clear
	   the EVP_PKEY_CTX assigned to	ctx. In	such case, freeing the cleared
	   EVP_PKEY_CTX	or not depends on how the EVP_PKEY_CTX is created.

FLAGS
       EVP_MD_CTX_set_flags(), EVP_MD_CTX_clear_flags()	and
       EVP_MD_CTX_test_flags() can be used the manipulate and test these
       EVP_MD_CTX flags:

       EVP_MD_CTX_FLAG_ONESHOT
	   This	flag instructs the digest to optimize for one update only, if
	   possible.

       EVP_MD_CTX_FLAG_NO_INIT
	   This	flag instructs EVP_DigestInit()	and similar not	to initialise
	   the implementation specific data.

       EVP_MD_CTX_FLAG_FINALISE
	   Some	functions such as EVP_DigestSign only finalise copies of
	   internal contexts so	additional data	can be included	after the
	   finalisation	call.  This is inefficient if this functionality is
	   not required, and can be disabled with this flag.

RETURN VALUES
       EVP_DigestInit_ex(), EVP_DigestUpdate(),	EVP_DigestFinal_ex()
	   Returns 1 for success and 0 for failure.

       EVP_MD_CTX_ctrl()
	   Returns 1 if	successful or 0	for failure.

       EVP_MD_CTX_copy_ex()
	   Returns 1 if	successful or 0	for failure.

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

       EVP_MD_size(), EVP_MD_block_size(), EVP_MD_CTX_size(),
       EVP_MD_CTX_block_size()
	   Returns the digest or block size in bytes.

       EVP_md_null()
	   Returns a pointer to	the EVP_MD structure of	the "null" message
	   digest.

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

       EVP_MD_CTX_set_pkey_ctx()
	   This	function has no	return value.

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 SHA-2 (such as EVP_sha256(3)) or	the
       SHA-3 digest algorithms (such as	EVP_sha3_512(3)). 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.

       If digest contexts are not cleaned up after use,	memory leaks will
       occur.

       EVP_MD_CTX_size(), EVP_MD_CTX_block_size(), EVP_MD_CTX_type(),
       EVP_get_digestbynid() and EVP_get_digestbyobj() are defined as macros.

       EVP_MD_CTX_ctrl() sends commands	to message digests for additional
       configuration or	control.

EXAMPLES
       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 <string.h>
	#include <openssl/evp.h>

	int 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];
	    unsigned int md_len, i;

	    if (argv[1]	== NULL) {
		printf("Usage: mdtest digestname\n");
		exit(1);
	    }

	    md = EVP_get_digestbyname(argv[1]);
	    if (md == NULL) {
		printf("Unknown	message	digest %s\n", argv[1]);
		exit(1);
	    }

	    mdctx = EVP_MD_CTX_new();
	    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_free(mdctx);

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

	    exit(0);
	}

SEE ALSO
       dgst(1),	evp(7)

       The full	list of	digest algorithms are provided below.

       EVP_blake2b512(3), EVP_md2(3), EVP_md4(3), EVP_md5(3), EVP_mdc2(3),
       EVP_ripemd160(3), EVP_sha1(3), EVP_sha224(3), EVP_sha3_224(3),
       EVP_sm3(3), EVP_whirlpool(3)

HISTORY
       The EVP_MD_CTX_create() and EVP_MD_CTX_destroy()	functions were renamed
       to EVP_MD_CTX_new() and EVP_MD_CTX_free() in OpenSSL 1.1.0,
       respectively.

       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.

       The EVP_dss1() function was removed in OpenSSL 1.1.0.

       The EVP_MD_CTX_set_pkey_ctx() function was added	in 1.1.1.

COPYRIGHT
       Copyright 2000-2019 The OpenSSL Project Authors.	All Rights Reserved.

       Licensed	under the OpenSSL license (the "License").  You	may not	use
       this file except	in compliance with the License.	 You can obtain	a copy
       in the file LICENSE in the source distribution or at
       <https://www.openssl.org/source/license.html>.

1.1.1d				  2019-09-10		     EVP_DIGESTINIT(3)

NAME | SYNOPSIS | DESCRIPTION | FLAGS | RETURN VALUES | NOTES | EXAMPLES | SEE ALSO | HISTORY | COPYRIGHT

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