(PHP Extension) 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.

Chilkat PHP Downloads PHP Extension for Windows, Linux, MacOS, Alpine Linux, Solaris

<?php

include("chilkat.php");
// Use "chilkat_9_5_0.php" for versions of Chilkat < 10.0.0

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

$sb = new CkStringBuilder();
$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 CkPublicKey();
$success = $pubKey->LoadFromFile('rsaKeys/chilkat-rsa-2048.pem');
if ($success == false) {
    print $pubKey->lastErrorText() . "\n";
    exit;
}

$rsa = new CkRsa();
$rsa->ImportPublicKeyObj($pubKey);

// 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->put_Charset('utf-8');
$rsa->put_EncodingMode('base64');
$signedString = $sb->getAsString();
$success = $rsa->VerifyStringENC($signedString,'sha256',$base64_rsa_sig);

if ($success == false) {
    print $rsa->lastErrorText() . "\n";
    print 'Signature invalid.' . "\n";
}
else {
    print 'Signature valid.' . "\n";
}


?>