Perl

DSA Signature Create and Verify

See more DSA Examples

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.

Perl

use chilkat();

$success = 0;

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

$crypt = chilkat::CkCrypt2->new();

$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 = chilkat::CkDsa->new();

# 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() . "\r\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() . "\r\n";
    exit;
}

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

# 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() . "\r\n";
    exit;
}

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

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

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