(PHP Extension) DSA Signature Create and Verify

Shows how to create a DSA (DSS) signature for the contents of a file. The first step is to create an SHA-1 hash of the file contents. The hash is signed using the Digital Signature Algorithm and the signature bytes are retrieved as a hex-encoded string.

The 2nd part of the example loads the signature and verifies it against the hash.

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

<?php

// The version number (9_5_0) should match version of the Chilkat extension used, omitting the micro-version number.
// For example, if using Chilkat v9.5.0.48, then include as shown here:
include("chilkat_9_5_0.php");

// This example requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

$crypt = new CkCrypt2();

$crypt->put_EncodingMode('hex');
$crypt->put_HashAlgorithm('sha-1');

// Return the SHA-1 hash of a file.  The file may be any size.
// The Chilkat Crypt component will stream the file when 
// computing the hash, keeping the memory usage constant
// and reasonable.
// The 20-byte SHA-1 hash is returned as a hex-encoded string.
$hashStr = $crypt->hashFileENC('hamlet.xml');

$dsa = new CkDsa();

// Load a DSA private key from a PEM file.  Chilkat DSA
// provides the ability to load and save DSA public and private
// keys from encrypted or non-encrypted PEM or DER.
// The LoadText method is for convenience only.  You may
// use any means to load the contents of a PEM file into
// a string.

$pemPrivateKey = $dsa->loadText('dsa_priv.pem');
$success = $dsa->FromPem($pemPrivateKey);
if ($success != true) {
    print $dsa->lastErrorText() . "\n";
    exit;
}

// You may optionally verify the key to ensure that it is a valid
// DSA key.
$success = $dsa->VerifyKey();
if ($success != true) {
    print $dsa->lastErrorText() . "\n";
    exit;
}

// Load the hash to be signed into the DSA object:
$success = $dsa->SetEncodedHash('hex',$hashStr);
if ($success != true) {
    print $dsa->lastErrorText() . "\n";
    exit;
}

// Now that the DSA object contains both the private key and hash,
// it is ready to create the signature:
$success = $dsa->SignHash();
if ($success != true) {
    print $dsa->lastErrorText() . "\n";
    exit;
}

// If SignHash is successful, the DSA object contains the
// signature.  It may be accessed as a hex or base64 encoded
// string.  (It is also possible to access directly in byte array form via
// the "Signature" property.)
$hexSig = $dsa->getEncodedSignature('hex');
print 'Signature:' . "\n";
print $hexSig . "\n";

// -----------------------------------------------------------
// Step 2: Verify the DSA Signature
// -----------------------------------------------------------

$dsa2 = new CkDsa();

// Load the DSA public key to be used for verification:

$pemPublicKey = $dsa2->loadText('dsa_pub.pem');
$success = $dsa2->FromPublicPem($pemPublicKey);
if ($success != true) {
    print $dsa2->lastErrorText() . "\n";
    exit;
}

// Load the hash to be verified against the signature.
$success = $dsa2->SetEncodedHash('hex',$hashStr);
if ($success != true) {
    print $dsa2->lastErrorText() . "\n";
    exit;
}

// Load the signature:
$success = $dsa2->SetEncodedSignature('hex',$hexSig);
if ($success != true) {
    print $dsa2->lastErrorText() . "\n";
    exit;
}

// Verify:
$success = $dsa2->Verify();
if ($success != true) {
    print $dsa2->lastErrorText() . "\n";
}
else {
    print 'DSA Signature Verified!' . "\n";
}


?>