Perl

DSA R,S Signature Values

See more DSA Examples

Creates a DSA signature. Gets r,s values from the signature. Re-creates the DSA signature ASN.1 from the r,s values. Then verifies the signature using the re-created ASN.1 DSA signature. 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");

$hashStr = $crypt->hashFileENC("qa_data/hamlet.xml");
print "hash to sign: " . $hashStr . "\r\n";

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

$pemPrivateKey = $dsa->loadText("qa_data/dsa/dsaPrivKey2.pem");
$success = $dsa->FromPem($pemPrivateKey);
if ($success == 0) {
    print $dsa->lastErrorText() . "\r\n";
    exit;
}

# Load the hash to be signed into the DSA object:
$success = $dsa->SetEncodedHash("hex",$hashStr);
if ($success == 0) {
    print $dsa->lastErrorText() . "\r\n";
    exit;
}

# Sign the hash.
$success = $dsa->SignHash();
if ($success == 0) {
    print $dsa->lastErrorText() . "\r\n";
    exit;
}

# Get the ASN.1 signature.
$asnSig = $dsa->getEncodedSignature("base64");
print "Signature: " . $asnSig . "\r\n";

# Examine the details of the ASN.1 signature.
# We want to get the r,s values as hex strings..
$asn = chilkat::CkAsn->new();
$success = $asn->LoadEncoded($asnSig,"base64");
if ($success == 0) {
    print $asn->lastErrorText() . "\r\n";
    exit;
}

# Get the ASN.1 as XML.
$xml = chilkat::CkXml->new();
$success = $xml->LoadXml($asn->asnToXml());
print "Signature as XML: " . "\r\n";
print $xml->getXml() . "\r\n";

# Sample XML shown here.
# The r and s values are the two hex strings in the XML.

# <?xml version="1.0" encoding="utf-8"?>
# <sequence>
#     <int>2C187F3AB6E47A66497B86CE97BB39E2133810F5</int>
#     <int>588E53D3F7B69636B48FD7175E99A3961BD7D775</int>
# </sequence>

# Pretend we're starting with r,s
$r = "2C187F3AB6E47A66497B86CE97BB39E2133810F5";
$s = "588E53D3F7B69636B48FD7175E99A3961BD7D775";

# Build the XML that will be converted to ASN.1
$xml->Clear();
$xml->put_Tag("sequence");
$xml->NewChild2("int",$r);
$xml->NewChild2("int",$s);

# Convert the XML to ASN.1
$success = $asn->LoadAsnXml($xml->getXml());

# Emit the signature as DER encoded ASN.1 (base64)
$asnSig = $asn->getEncodedDer("base64");

# --------------------------------------------------------------------
# Verify the signature using the asnSig we built from the r,s values
# --------------------------------------------------------------------

$dsa2 = chilkat::CkDsa->new();

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

$pemPublicKey = $dsa2->loadText("qa_data/dsa/dsaPubKey2.pem");
$success = $dsa2->FromPublicPem($pemPublicKey);
if ($success == 0) {
    print $dsa2->lastErrorText() . "\r\n";
    exit;
}

# Load the hash to be verified.
$success = $dsa2->SetEncodedHash("hex",$hashStr);
if ($success == 0) {
    print $dsa2->lastErrorText() . "\r\n";
    exit;
}

# Load the ASN.1 signature:
$success = $dsa2->SetEncodedSignature("base64",$asnSig);
if ($success == 0) {
    print $dsa2->lastErrorText() . "\r\n";
    exit;
}

# Verify:
$success = $dsa2->Verify();
if ($success == 0) {
    print $dsa2->lastErrorText() . "\r\n";
}
else {
    print "DSA Signature Verified!" . "\r\n";
}