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EVP_DIGESTSIGNINIT(3)		    OpenSSL		 EVP_DIGESTSIGNINIT(3)

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

SYNOPSIS
	#include <openssl/evp.h>

	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.

       EVP_DigestSignInit() sets up signing context ctx	to use digest type
       from ENGINE e and private key pkey. 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() (which
       means the EVP_PKEY_CTX is created inside	EVP_DigestSignInit() and it
       will be freed automatically when	the EVP_MD_CTX is freed).

       The digest type may be NULL if the signing algorithm supports it.

       No EVP_PKEY_CTX will be created by EVP_DigestSignInit() if the passed
       ctx has already been assigned one via EVP_MD_CTX_set_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_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. This	function is currently implemented
       using a macro.

       EVP_DigestSignFinal() signs the data in ctx and places the signature in
       sig.  If	sig is NULL then the maximum 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_DigestSignaFinal()
       and EVP_DigestSign() return 1 for success and 0 or a negative value for
       failure.	In particular, a return	value of -2 indicates the operation is
       not supported by	the public key algorithm.

       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_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_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), dgst(1),	RAND(7)

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

COPYRIGHT
       Copyright 2006-2019 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_DIGESTSIGNINIT(3)

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

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