How to create signature using SHA256WithRSA and PKCS#8 in PHP

Question

I wants to write the functionality to create a signature using the algorithem of SHA256withRSA, I have tried but nothing is printing.Can anyone please update my code. I have tried but I am not able to identify my mistake. Thnaks in advance!!

My PHP code

<?php

$data = "Sample Text";

$private_key = <<<EOD
-----BEGIN RSA PRIVATE KEY-----
MIIBOgIBAAJBANDiE2+Xi/WnO+s120NiiJhNyIButVu6zxqlVzz0wy2j4kQVUC4Z
RZD80IY+4wIiX2YxKBZKGnd2TtPkcJ/ljkUCAwEAAQJAL151ZeMKHEU2c1qdRKS9
sTxCcc2pVwoAGVzRccNX16tfmCf8FjxuM3WmLdsPxYoHrwb1LFNxiNk1MXrxjH3R
6QIhAPB7edmcjH4bhMaJBztcbNE1VRCEi/bisAwiPPMq9/2nAiEA3lyc5+f6DEIJ
h1y6BWkdVULDSM+jpi1XiV/DevxuijMCIQCAEPGqHsF+4v7Jj+3HAgh9PU6otj2n
Y79nJtCYmvhoHwIgNDePaS4inApN7omp7WdXyhPZhBmulnGDYvEoGJN66d0CIHra
I2SvDkQ5CmrzkW5qPaE2oO7BSqAhRZxiYpZFb5CI
-----END RSA PRIVATE KEY-----
EOD;

$binary_signature = "";

$algo = "SHA256WithRSA";
openssl_sign($data, $binary_signature, $private_key, $algo);
$signature = base64_encode($binary_signature);
echo $timestamp = time();// I need here PHP curent date and timestamp
echo "<br>";
print_r($signature);

?>

UPDATED PHP CODE

<?php
$data = "Sample Text";

$private_key = <<<EOD
-----BEGIN RSA PRIVATE KEY-----
MIIBOgIBAAJBANDiE2+Xi/WnO+s120NiiJhNyIButVu6zxqlVzz0wy2j4kQVUC4Z
RZD80IY+4wIiX2YxKBZKGnd2TtPkcJ/ljkUCAwEAAQJAL151ZeMKHEU2c1qdRKS9
sTxCcc2pVwoAGVzRccNX16tfmCf8FjxuM3WmLdsPxYoHrwb1LFNxiNk1MXrxjH3R
6QIhAPB7edmcjH4bhMaJBztcbNE1VRCEi/bisAwiPPMq9/2nAiEA3lyc5+f6DEIJ
h1y6BWkdVULDSM+jpi1XiV/DevxuijMCIQCAEPGqHsF+4v7Jj+3HAgh9PU6otj2n
Y79nJtCYmvhoHwIgNDePaS4inApN7omp7WdXyhPZhBmulnGDYvEoGJN66d0CIHra
I2SvDkQ5CmrzkW5qPaE2oO7BSqAhRZxiYpZFb5CI
-----END RSA PRIVATE KEY-----
EOD;

$binary_signature = "";

$algo = OPENSSL_ALGO_SHA256;
openssl_sign($data, $binary_signature, $private_key, $algo);
$signature = base64_encode($binary_signature);

//verify signature
$r = openssl_verify($data, $signature, $public_key_pem, "sha256WithRSAEncryption");
var_dump($r);
?>

Turn your error reporting on/up and you'll see "PHP Warning: openssl_sign(): Unknown signature algorithm." Use the constant OPENSSL_ALGO_SHA256 and you'll get the signature "xEjyq+pwgRLpc+ikNT8HQRiE+vYtHjwaBafhaqW1ueu8ftxvg1PDtPZ1jQGjwvtuixk+yg90nbpjF0nUBshqNA==" — Sammitch
– Sammitch, Commented Jul 25, 2022 at 19:35
I am using OPENSSL_ALGO_SHA256 getting error ( ! ) Warning: openssl_sign(): Unknown signature algorithm. in C:\xampp\htdocs\test\index.php on line 20 — RAJA
– RAJA, Commented Jul 25, 2022 at 19:38

oralunal · Accepted Answer · 2022-07-25 19:55:41Z

3

You can view a good example on PHP.net. In the below example, it generates and saves private_key.pem, public_key.pem and signature.dat.

There are built-in algorithm constants. You can view them here. You have to use these as Constant. Example: openssl_sign(data, $signature, $pkeyid, OPENSSL_ALGO_SHA256)

Also, you can check any other algorithm by running openssl_get_md_methods(). You can see more detail here. Notice that these algorithms are not constant. You have to define these ones as a string. Example: openssl_sign(data, $signature, $pkeyid, 'sha256')

<?php
//data you want to sign
$data = 'my data';

//create new private and public key
$new_key_pair = openssl_pkey_new(array(
    "private_key_bits" => 2048,
    "private_key_type" => OPENSSL_KEYTYPE_RSA,
));
openssl_pkey_export($new_key_pair, $private_key_pem);

$details = openssl_pkey_get_details($new_key_pair);
$public_key_pem = $details['key'];

//create signature
openssl_sign($data, $signature, $private_key_pem, OPENSSL_ALGO_SHA256);

//save for later
file_put_contents('private_key.pem', $private_key_pem);
file_put_contents('public_key.pem', $public_key_pem);
file_put_contents('signature.dat', $signature);

//verify signature
$r = openssl_verify($data, $signature, $public_key_pem, "sha256WithRSAEncryption");
var_dump($r);
?>

EDIT

In your situation, please try the below code:

$data = "Sample Text";

$private_key = <<<EOD
-----BEGIN RSA PRIVATE KEY-----
MIIBOgIBAAJBANDiE2+Xi/WnO+s120NiiJhNyIButVu6zxqlVzz0wy2j4kQVUC4Z
RZD80IY+4wIiX2YxKBZKGnd2TtPkcJ/ljkUCAwEAAQJAL151ZeMKHEU2c1qdRKS9
sTxCcc2pVwoAGVzRccNX16tfmCf8FjxuM3WmLdsPxYoHrwb1LFNxiNk1MXrxjH3R
6QIhAPB7edmcjH4bhMaJBztcbNE1VRCEi/bisAwiPPMq9/2nAiEA3lyc5+f6DEIJ
h1y6BWkdVULDSM+jpi1XiV/DevxuijMCIQCAEPGqHsF+4v7Jj+3HAgh9PU6otj2n
Y79nJtCYmvhoHwIgNDePaS4inApN7omp7WdXyhPZhBmulnGDYvEoGJN66d0CIHra
I2SvDkQ5CmrzkW5qPaE2oO7BSqAhRZxiYpZFb5CI
-----END RSA PRIVATE KEY-----
EOD;

$binary_signature = "";

$algo = OPENSSL_ALGO_SHA256;
openssl_sign($data, $binary_signature, $private_key, $algo);
$signature = base64_encode($binary_signature);
echo $timestamp = time();// I need here PHP curent date and timestamp
echo "<br>";
print_r($signature);

edited Jul 25, 2022 at 19:55

answered Jul 25, 2022 at 19:46

oralunal

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11 Comments

RAJA Over a year ago

I tried your code, throwing warning message, signature not getting created

oralunal Over a year ago

What is the warning message? Again "Warning: openssl_sign(): Unknown signature algorithm"?

RAJA Over a year ago

OPENSSL_ALGO_SHA256 is equivalent to SHA256withRSA this? because i wants to implement in SHA256withRSA

RAJA Over a year ago

your Edit answer working fine. OPENSSL_ALGO_SHA256 is equivalent to SHA256withRSA this?

oralunal Over a year ago

yes, you can verify it with this: openssl_verify($data, $signature, $public_key_pem, "sha256WithRSAEncryption");

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