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.

Chilkat2 Perl

use strict;
use warnings;
use Chilkat2;

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

my $crypt = Chilkat2::Crypt2->new;

$crypt->EncodingMode('hex');
$crypt->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.
my $hashStr = $crypt->HashFileENC('hamlet.xml');

my $dsa = Chilkat2::Dsa->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.
my $pemPrivateKey = $dsa->LoadText('dsa_priv.pem');
my $success = $dsa->FromPem($pemPrivateKey);
if (!$success) {
    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) {
    print $dsa->LastErrorText, "\n";
    exit;
}

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

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

my $dsa2 = Chilkat2::Dsa->new;

# Load the DSA public key to be used for verification:
my $pemPublicKey = $dsa2->LoadText('dsa_pub.pem');
$success = $dsa2->FromPublicPem($pemPublicKey);
if (!$success) {
    print $dsa2->LastErrorText, "\n";
    exit;
}

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

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

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