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 Perl Module Downloads for Windows, Linux, and MAC OS X

use chilkat();



#  Use Chilkat Crypt to hash the contents of a file.
$crypt = new chilkat::CkCrypt2();
$success = $crypt->UnlockComponent("Anything for 30-day trial.");
if ($success != 1) {
    print $crypt->lastErrorText() . "\n";
    exit;
}

$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 chilkat::CkDsa();

#  The Chilkat Crypt and Chilkat DSA components are separate
#  products.  To license both, it's least expensive to purchase
#  the "Chilkat Bundle" which provides licenses to all the
#  Chilkat components.
$success = $dsa->UnlockComponent("Anything for 30-day trial");
if ($success != 1) {
    print $dsa->lastErrorText() . "\n";
    exit;
}

#  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 != 1) {
    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 != 1) {
    print $dsa->lastErrorText() . "\n";
    exit;
}

#  Load the hash to be signed into the DSA object:
$success = $dsa->SetEncodedHash("hex",$hashStr);
if ($success != 1) {
    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 != 1) {
    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:" . "\r\n";
print $hexSig . "\r\n";

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

$dsa2 = new chilkat::CkDsa();

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

$pemPublicKey = $dsa2->loadText("dsa_pub.pem");
$success = $dsa2->FromPublicPem($pemPublicKey);
if ($success != 1) {
    print $dsa2->lastErrorText() . "\n";
    exit;
}

#  Load the hash to be verified against the signature.
$success = $dsa2->SetEncodedHash("hex",$hashStr);
if ($success != 1) {
    print $dsa2->lastErrorText() . "\n";
    exit;
}

#  Load the signature:
$success = $dsa2->SetEncodedSignature("hex",$hexSig);
if ($success != 1) {
    print $dsa2->lastErrorText() . "\n";
    exit;
}

#  Verify:
$success = $dsa2->Verify();
if ($success != 1) {
    print $dsa2->lastErrorText() . "\n";
}
else {
    print "DSA Signature Verified!" . "\r\n";
}