PHP Requires Chilkat v11.0.0+

Verify an RSA Signature Against the Signed String

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Demonstrates how to validate an RSA Signature against the string that was signed. Chilkat2 PHP

<?php

use Chilkat2\PublicKey;
use Chilkat2\Rsa;
use Chilkat2\StringBuilder;

// Create the same string we previously signed in this example:
// RSA Sign utf-8 Bytes of String to get Base64 RSA Signature

$sb = new StringBuilder();
$crlfLineEnding = true;
for ($i = 0; $i <= 10; $i++) {
    $sb->AppendLine('This is a test.', $crlfLineEnding);
}

$base64_rsa_sig = 'gWgpEXQqvXN6wh0MuFXPiw2xCb8cnmdizBT1TD1Tpm2GlJ8gnD59DGSj35GGXk1tM+mCOvMa2uW/9gmz8p6A90JLbn918i/2wKGvcde4wXnzPO7JADSNn2UwYzf3rp4/q/JrHv1GZETRJhABSFqTxOgdmdbEJQE/zijOSctCtQAM2CTb6t2BO8uHKSSUAwPH2cbeWxqsaVRLT4ruk5nZOxhoLgLMSjupiSzbE8zSTkkFOEHD+Mbb2xwg85AI0E4DsUnp+hLwwtS0blesgSyvtBY8oJODJeFcJsR7JDOTPdzHQHgJRl/2A4ij5xT91TpXy7ok43jhT6O9j7Q3qrafIQ==';

// Get the public key to be used for signature verification.
$pubKey = new PublicKey();
try {
    $pubKey->LoadFromFile('rsaKeys/chilkat-rsa-2048.pem');

    $rsa = new Rsa();
    $rsa->UsePublicKey($pubKey);
} catch (\Chilkat2\Exception $e) {
    echo $e->getMessage(), "\n";
    exit;
}

// Verify the string against the signature.
// We signed the utf-8 byte representation of the string, so we must indicate
// to also validate against the utf-8 byte representation.
$rsa->Charset = 'utf-8';
$rsa->EncodingMode = 'base64';
$signedString = $sb->GetAsString();

try {
    $rsa->VerifyStringENC($signedString, 'sha256', $base64_rsa_sig);
    echo "Signature valid.\n";
} catch (\Chilkat2\Exception $e) {
    echo $e->getMessage(), "\n";
    echo "Signature invalid.\n";
}