NAME

       EVP_PKEY_verify_init, EVP_PKEY_verify_init_ex, 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_init_ex(EVP_PKEY_CTX *ctx, const OSSL_PARAM params[]);
        int EVP_PKEY_verify(EVP_PKEY_CTX *ctx,
                            const unsigned char *sig, size_t siglen,
                            const unsigned char *tbs, size_t tbslen);

DESCRIPTION

       EVP_PKEY_verify_init() initializes a public key algorithm context ctx for signing using
       the algorithm given when the context was created using EVP_PKEY_CTX_new(3) or variants
       thereof.  The algorithm is used to fetch a EVP_SIGNATURE method implicitly, see "Implicit
       fetch" in provider(7) for more information about implicit fetches.

       EVP_PKEY_verify_init_ex() is the same as EVP_PKEY_verify_init() but additionally sets the
       passed parameters params on the context before returning.

       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.

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.
         */

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

       The EVP_PKEY_verify_init() and EVP_PKEY_verify() functions were added in OpenSSL 1.0.0.

       The EVP_PKEY_verify_init_ex() function was added 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>.