=pod

=head1 NAME

EVP_PKEY_verify_init, EVP_PKEY_verify - signature verification using a public key algorithm

=head1 SYNOPSIS

 #include <openssl/evp.h>

 int EVP_PKEY_verify_init(EVP_PKEY_CTX *ctx);

 int EVP_PKEY_verify(EVP_PKEY_CTX *ctx,

                     const unsigned char *sig, size_t siglen,

                     const unsigned char *tbs, size_t tbslen);

=head1 DESCRIPTION

The EVP_PKEY_verify_init() function initializes a public key algorithm

context using key B<pkey> for a signature verification operation.

The EVP_PKEY_verify() function performs a public key verification operation

using B<ctx>. The signature is specified using the B<sig> and

B<siglen> parameters. The verified data (i.e. the data believed originally

signed) is specified using the B<tbs> and B<tbslen> parameters.

=head1 NOTES

After the call to EVP_PKEY_verify_init() algorithm specific control

operations can be performed to set any appropriate parameters for the

operation.

The function EVP_PKEY_verify() can be called more than once on the same

context if several operations are performed using the same parameters.

=head1 RETURN VALUES

EVP_PKEY_verify_init() and EVP_PKEY_verify() return 1 if the verification was

successful and 0 if it failed. Unlike other functions the return value 0 from

EVP_PKEY_verify() only indicates that the signature did not verify

successfully (that is tbs did not match the original data or the signature was

of invalid form) it is not an indication of a more serious error.

A negative value indicates an error other that signature verification failure.

In particular a return value of -2 indicates the operation is not supported by

the public key algorithm.

=head1 EXAMPLES

Verify signature using PKCS#1 and SHA256 digest:

 #include <openssl/evp.h>

 #include <openssl/rsa.h>

 EVP_PKEY_CTX *ctx;

 unsigned char *md, *sig;

 size_t mdlen, siglen;

 EVP_PKEY *verify_key;

 /*

  * NB: assumes verify_key, sig, siglen md and mdlen are already set up

  * and that verify_key is an RSA public key

  */

 ctx = EVP_PKEY_CTX_new(verify_key, NULL /* no engine */);

 if (!ctx)

     /* Error occurred */

 if (EVP_PKEY_verify_init(ctx) <= 0)

     /* Error */

 if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) <= 0)

     /* Error */

 if (EVP_PKEY_CTX_set_signature_md(ctx, EVP_sha256()) <= 0)

     /* Error */

 /* Perform operation */

 ret = EVP_PKEY_verify(ctx, sig, siglen, md, mdlen);

 /*

  * ret == 1 indicates success, 0 verify failure and < 0 for some

  * other error.

  */

=head1 SEE ALSO

L<EVP_PKEY_CTX_new(3)>,

L<EVP_PKEY_encrypt(3)>,

L<EVP_PKEY_decrypt(3)>,

L<EVP_PKEY_sign(3)>,

L<EVP_PKEY_verify_recover(3)>,

L<EVP_PKEY_derive(3)>

=head1 HISTORY

These functions were added in OpenSSL 1.0.0.

=head1 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

L<https://www.openssl.org/source/license.html>.

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