PHP openssl_verify() Function

The openssl_verify() function is an inbuilt function in PHP which is used to verifies that if the signature is correct for the specified data using the public key associated with public_key or not. This must be the public key corresponding to the private key used for signing.

Syntax: 

openssl_verify( $data, $signature, 
    $public_key, $algorithm ): int|false

Parameters: This function accept four parameters which are listed below –

• data: The string of data used to generate the signature previously.
• signature: A raw binary string, generated by openssl_sign() or similar means.
• public_key: string – a PEM formatted key, example, “—–BEGIN PUBLIC KEY—– MIIBCgK…”
• algorithm: A valid string returned by openssl_get_md_methods() function.

Return Value: It returns 1 if the signature is correct, 0 if it is incorrect, and -1 or false on error.

Note: The public key comes from a certificate in any of the support formats.

Listed below are examples illustrating the use of openssl_verify() function:

Example 1:

PHP

<?php

// Data you want to sign
$data = 'geeks for geeks';

// Create a new pair of private and public key
$private_key_rsa = openssl_pkey_new(array(
    "private_key_bits" => 2048,
    "private_key_type" => OPENSSL_KEYTYPE_RSA,
));

$details = openssl_pkey_get_details($private_key_rsa);
$public_key_rsa = openssl_pkey_get_public($details['key']);

// Create signature for your data
openssl_sign($data, $signature,
    $private_key_rsa, "sha256WithRSAEncryption");

// Verify signature obtained for your data
$result = openssl_verify($data, $signature,
    $public_key_rsa, OPENSSL_ALGO_SHA256);

if ($result == 1) {
    echo "signature is valid for given data.";
} elseif ($ok == 0) {
    echo "signature is invalid for given data.";
} else {
    echo "error: ".openssl_error_string();
}

?>

Output:

signature is valid for given data.

Example 2:

PHP

<?php

// Data you want to sign
$data = 'geeks for geeks';

// Create a new pair of private and public key
$private_key_rsa = openssl_pkey_new(array(
    "private_key_bits" => 2048,
    "private_key_type" => OPENSSL_KEYTYPE_RSA,
));

$details = openssl_pkey_get_details($private_key_rsa);
$public_key_rsa = openssl_pkey_get_public($details['key']);

// Create signature for your data
openssl_sign($data, $signature,
    $private_key_rsa, "sha256WithRSAEncryption");

// Change the data
$data = 'geeks and geeks';

// Verify signature obtained for your data
$result = openssl_verify($data, $signature,
    $public_key_rsa, OPENSSL_ALGO_SHA256);

if ($result == 1) {
    echo "signature is valid for given data.";
} elseif ($ok == 0) {
    echo "signature is invalid for given data.";
} else {
    echo "error: ".openssl_error_string();
}
?>

Output:

signature is invalid for given data.

Reference: https://www.php.net/manual/en/function.openssl-verify.php