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EVP_VERIFYINIT(3)		    OpenSSL		     EVP_VERIFYINIT(3)

NAME
       EVP_VerifyInit_ex, EVP_VerifyInit, EVP_VerifyUpdate, EVP_VerifyFinal -
       EVP signature verification functions

SYNOPSIS
	#include <openssl/evp.h>

	int EVP_VerifyInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
	int EVP_VerifyUpdate(EVP_MD_CTX	*ctx, const void *d, unsigned int cnt);
	int EVP_VerifyFinal(EVP_MD_CTX *ctx, unsigned char *sigbuf, unsigned int siglen,
			    EVP_PKEY *pkey);

	int EVP_VerifyInit(EVP_MD_CTX *ctx, const EVP_MD *type);

DESCRIPTION
       The EVP signature verification routines are a high level	interface to
       digital signatures.

       EVP_VerifyInit_ex() sets	up verification	context	ctx to use digest type
       from ENGINE impl. ctx must be created by	calling	EVP_MD_CTX_new()
       before calling this function.

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

       EVP_VerifyFinal() verifies the data in ctx using	the public key pkey
       and against the siglen bytes at sigbuf.

       EVP_VerifyInit()	initializes verification context ctx to	use the
       default implementation of digest	type.

RETURN VALUES
       EVP_VerifyInit_ex() and EVP_VerifyUpdate() return 1 for success and 0
       for failure.

       EVP_VerifyFinal() returns 1 for a correct signature, 0 for failure and
       -1 if some other	error occurred.

       The error codes can be obtained by 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.

       The call	to EVP_VerifyFinal() internally	finalizes a copy of the	digest
       context.	 This means that calls to EVP_VerifyUpdate() and
       EVP_VerifyFinal() can be	called later to	digest and verify 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.

BUGS
       Older versions of this documentation wrongly stated that	calls to
       EVP_VerifyUpdate() could	not be made after calling EVP_VerifyFinal().

       Since the public	key is passed in the call to EVP_SignFinal() any error
       relating	to the private key (for	example	an unsuitable key and digest
       combination) will not be	indicated until	after potentially large
       amounts of data have been passed	through	EVP_SignUpdate().

       It is not possible to change the	signing	parameters using these
       function.

       The previous two	bugs are fixed in the newer EVP_VerifyDigest*()
       function.

SEE ALSO
       evp(7), EVP_SignInit(3),	EVP_DigestInit(3), evp(7), HMAC(3), MD2(3),
       MD5(3), MDC2(3),	RIPEMD160(3), SHA1(3), dgst(1)

COPYRIGHT
       Copyright 2000-2018 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>.

1.1.1a				  2018-11-20		     EVP_VERIFYINIT(3)

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

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