- NAME
- SYNOPSIS
- DESCRIPTION
- NOTES
- RETURN VALUES
- EXAMPLE
- SEE ALSO
- HISTORY

# 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 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);
     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, EVP_PKEY_encrypt, EVP_PKEY_decrypt, EVP_PKEY_sign, EVP_PKEY_verify_recover, EVP_PKEY_derive

# HISTORY

These functions were first added to OpenSSL 1.0.0.