NAME

       EVP_PKEY_verify_init, EVP_PKEY_verify - signature verification using a public key
       algorithm

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);

DESCRIPTION

       The EVP_PKEY_verify_init() function initializes a public key algorithm context using key
       pkey for a signature verification operation.

       The EVP_PKEY_verify() function performs a public key verification operation using ctx. The
       signature is specified using the sig and siglen parameters. The verified data (i.e. the
       data believed originally signed) is specified using the tbs and tbslen parameters.

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.

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.

EXAMPLE

       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.
         */

SEE ALSO

       EVP_PKEY_CTX_new(3), EVP_PKEY_encrypt(3), EVP_PKEY_decrypt(3), EVP_PKEY_sign(3),
       EVP_PKEY_verify_recover(3), EVP_PKEY_derive(3)

HISTORY

       These functions were first added to OpenSSL 1.0.0.

COPYRIGHT

       Copyright 2006-2018 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>.