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EVP_DIGESTSIGNINIT(3ossl)	    OpenSSL	     EVP_DIGESTSIGNINIT(3ossl)

NAME
       EVP_DigestSignInit_ex, EVP_DigestSignInit, EVP_DigestSignUpdate,
       EVP_DigestSignFinal, EVP_DigestSign - EVP signing functions

SYNOPSIS
	#include <openssl/evp.h>

	int EVP_DigestSignInit_ex(EVP_MD_CTX *ctx, EVP_PKEY_CTX	**pctx,
				  const	char *mdname, OSSL_LIB_CTX *libctx,
				  const	char *props, EVP_PKEY *pkey);
	int EVP_DigestSignInit(EVP_MD_CTX *ctx,	EVP_PKEY_CTX **pctx,
			       const EVP_MD *type, ENGINE *e, EVP_PKEY *pkey);
	int EVP_DigestSignUpdate(EVP_MD_CTX *ctx, const	void *d, size_t	cnt);
	int EVP_DigestSignFinal(EVP_MD_CTX *ctx, unsigned char *sig, size_t *siglen);

	int EVP_DigestSign(EVP_MD_CTX *ctx, unsigned char *sigret,
			   size_t *siglen, const unsigned char *tbs,
			   size_t tbslen);

DESCRIPTION
       The EVP signature routines are a	high-level interface to	digital
       signatures.  Input data is digested first before	the signing takes
       place.

       EVP_DigestSignInit_ex() sets up signing context ctx to use a digest
       with the	name mdname and	private	key pkey. The name of the digest to be
       used is passed to the provider of the signature algorithm in use. How
       that provider interprets	the digest name	is provider specific. The
       provider	may implement that digest directly itself or it	may
       (optionally) choose to fetch it (which could result in a	digest from a
       different provider being	selected). If the provider supports fetching
       the digest then it may use the props argument for the properties	to be
       used during the fetch.

       The pkey	algorithm is used to fetch a EVP_SIGNATURE method implicitly,
       to be used for the actual signing. See "Implicit	fetch" in provider(7)
       for more	information about implicit fetches.

       The OpenSSL default and legacy providers	support	fetching digests and
       can fetch those digests from any	available provider. The	OpenSSL	fips
       provider	also supports fetching digests but will	only fetch digests
       that are	themselves implemented inside the fips provider.

       ctx must	be created with	EVP_MD_CTX_new() before	calling	this function.
       If pctx is not NULL, the	EVP_PKEY_CTX of	the signing operation will be
       written to *pctx: this can be used to set alternative signing options.
       Note that any existing value in *pctx is	overwritten. The EVP_PKEY_CTX
       value returned must not be freed	directly by the	application if ctx is
       not assigned an EVP_PKEY_CTX value before being passed to
       EVP_DigestSignInit_ex() (which means the	EVP_PKEY_CTX is	created	inside
       EVP_DigestSignInit_ex() and it will be freed automatically when the
       EVP_MD_CTX is freed). If	the EVP_PKEY_CTX to be used is created by
       EVP_DigestSignInit_ex then it will use the OSSL_LIB_CTX specified in
       libctx and the property query string specified in props.

       The digest mdname may be	NULL if	the signing algorithm supports it. The
       props argument can always be NULL.

       No EVP_PKEY_CTX will be created by EVP_DigestSignInit_ex() if the
       passed ctx has already been assigned one	via
       EVP_MD_CTX_set_pkey_ctx(3).  See	also SM2(7).

       Only EVP_PKEY types that	support	signing	can be used with these
       functions. This includes	MAC algorithms where the MAC generation	is
       considered as a form of "signing". Built-in EVP_PKEY types supported by
       these functions are CMAC, Poly1305, DSA,	ECDSA, HMAC, RSA, SipHash,
       Ed25519 and Ed448.

       Not all digests can be used for all key types. The following
       combinations apply.

       DSA Supports SHA1, SHA224, SHA256, SHA384 and SHA512

       ECDSA
	   Supports SHA1, SHA224, SHA256, SHA384, SHA512 and SM3

       RSA with	no padding
	   Supports no digests (the digest type	must be	NULL)

       RSA with	X931 padding
	   Supports SHA1, SHA256, SHA384 and SHA512

       All other RSA padding types
	   Support SHA1, SHA224, SHA256, SHA384, SHA512, MD5, MD5_SHA1,	MD2,
	   MD4,	MDC2, SHA3-224,	SHA3-256, SHA3-384, SHA3-512

       Ed25519 and Ed448
	   Support no digests (the digest type must be NULL)

       HMAC
	   Supports any	digest

       CMAC, Poly1305 and SipHash
	   Will	ignore any digest provided.

       If RSA-PSS is used and restrictions apply then the digest must match.

       EVP_DigestSignInit() works in the same way as EVP_DigestSignInit_ex()
       except that the mdname parameter	will be	inferred from the supplied
       digest type, and	props will be NULL. Where supplied the ENGINE e	will
       be used for the signing and digest algorithm implementations. e may be
       NULL.

       EVP_DigestSignUpdate() hashes cnt bytes of data at d into the signature
       context ctx. This function can be called	several	times on the same ctx
       to include additional data.

       Unless sig is NULL EVP_DigestSignFinal()	signs the data in ctx and
       places the signature in sig.  Otherwise the maximum necessary size of
       the output buffer is written to the siglen parameter. If	sig is not
       NULL then before	the call the siglen parameter should contain the
       length of the sig buffer. If the	call is	successful the signature is
       written to sig and the amount of	data written to	siglen.

       EVP_DigestSign()	signs tbslen bytes of data at tbs and places the
       signature in sig	and its	length in siglen in a similar way to
       EVP_DigestSignFinal().

RETURN VALUES
       EVP_DigestSignInit(), EVP_DigestSignUpdate(), EVP_DigestSignFinal() and
       EVP_DigestSign()	return 1 for success and 0 for failure.

       The error codes can be obtained from ERR_get_error(3).

NOTES
       The EVP interface to digital signatures should almost always be used in
       preference to the low-level interfaces. This is because the code	then
       becomes transparent to the algorithm used and much more flexible.

       EVP_DigestSign()	is a one shot operation	which signs a single block of
       data in one function. For algorithms that support streaming it is
       equivalent to calling EVP_DigestSignUpdate() and	EVP_DigestSignFinal().
       For algorithms which do not support streaming (e.g. PureEdDSA) it is
       the only	way to sign data.

       In previous versions of OpenSSL there was a link	between	message	digest
       types and public	key algorithms.	This meant that	"clone"	digests	such
       as EVP_dss1() needed to be used to sign using SHA1 and DSA. This	is no
       longer necessary	and the	use of clone digest is now discouraged.

       For some	key types and parameters the random number generator must be
       seeded.	If the automatic seeding or reseeding of the OpenSSL CSPRNG
       fails due to external circumstances (see	RAND(7)), the operation	will
       fail.

       The call	to EVP_DigestSignFinal() internally finalizes a	copy of	the
       digest context. This means that calls to	EVP_DigestSignUpdate() and
       EVP_DigestSignFinal() can be called later to digest and sign additional
       data.

       Since only a copy of the	digest context is ever finalized, the context
       must be cleaned up after	use by calling EVP_MD_CTX_free() or a memory
       leak will occur.

       The use of EVP_PKEY_get_size() with these functions is discouraged
       because some signature operations may have a signature length which
       depends on the parameters set. As a result EVP_PKEY_get_size() would
       have to return a	value which indicates the maximum possible signature
       for any set of parameters.

SEE ALSO
       EVP_DigestVerifyInit(3),	EVP_DigestInit(3), evp(7), HMAC(3), MD2(3),
       MD5(3), MDC2(3),	RIPEMD160(3), SHA1(3), openssl-dgst(1),	RAND(7)

HISTORY
       EVP_DigestSignInit(), EVP_DigestSignUpdate() and	EVP_DigestSignFinal()
       were added in OpenSSL 1.0.0.

       EVP_DigestSignInit_ex() was added in OpenSSL 3.0.

       EVP_DigestSignUpdate() was converted from a macro to a function in
       OpenSSL 3.0.

COPYRIGHT
       Copyright 2006-2021 The OpenSSL Project Authors.	All Rights Reserved.

       Licensed	under the Apache License 2.0 (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>.

3.0.0-beta1+quic		  2021-06-19	     EVP_DIGESTSIGNINIT(3ossl)

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

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