(Perl) ECDSA Sign Data and Get Raw R and S Values

Demonstrates getting the raw R and S value of an ECDSA signature.

Chilkat Perl Downloads Perl Module for Windows, MacOS, Linux, Alpine Linux, Solaris

use chilkat();

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

# To create an ECDSA signature, the data first needs to be hashed.  Then the hash
# is signed.

$crypt = chilkat::CkCrypt2->new();
$crypt->put_HashAlgorithm("SHA256");
$crypt->put_Charset("utf-8");
$crypt->put_EncodingMode("base64");

# Hash a string.
$hash1 = $crypt->hashStringENC("The quick brown fox jumps over the lazy dog");
print "hash1 = " . $hash1 . "\r\n";

# -----------------------------------------------------------
# An ECDSA private key is used for signing.  The public key is for signature verification.
# Load our ECC private key.
# Our private key file contains this:

# 	// -----BEGIN PRIVATE KEY-----
# 	MIGHAgEAMBMGByqGSM49AgEGCCqGSM49AwEHBG0wawIBAQQg3J8q/24D1sEKGdP9
# 	72MGYElLGpw/a56Y3t6pfON3uhShRANCAATlSmoizyhAwoYZAOuFBATl07/1RR54
# 	a1Dzfm16grxJe666AGKR+bSs24hk7TEpaeCTvT8YOOM3l+xKFg7zq6Q9
# 	-----END PRIVATE KEY-----

$privKey = chilkat::CkPrivateKey->new();
$success = $privKey->LoadPemFile("qa_data/ecc/secp256r1-key-pkcs8.pem");
if ($success != 1) {
    print $privKey->lastErrorText() . "\r\n";
    exit;
}

# Sign the hash..
$prng = chilkat::CkPrng->new();
$ecdsa = chilkat::CkEcc->new();
$ecdsaSigBase64 = $ecdsa->signHashENC($hash1,"base64",$privKey,$prng);
if ($ecdsa->get_LastMethodSuccess() != 1) {
    print $ecdsa->lastErrorText() . "\r\n";
    exit;
}

# The ECDSA signature is ASN.1 that contains a sequence of 2 large integers (r and s)
# For example:
# SEQUENCE (2 elem)
#   INTEGER (255 bit) 792134D9B4AD82D5431ED03835A88E2596EB35E5B13054BD9B05A0069281ACC9
#   INTEGER (255 bit) 481E758CC1E3CBF825537EC3D9A2CA627E5FAD1137BBEA65DF38658DCB0A9ED5

print "Base64 ECDSA signature = " . $ecdsaSigBase64 . "\r\n";

# If the raw R and S values are needed, here's how to get them:
$asn = chilkat::CkAsn->new();
$success = $asn->LoadEncoded($ecdsaSigBase64,"base64");
if ($success == 0) {
    print $asn->lastErrorText() . "\r\n";
    exit;
}

# The R and X will be in hexidecimal in the XML.
$xml = chilkat::CkXml->new();
$xml->LoadXml($asn->asnToXml());
print $xml->getXml() . "\r\n";

# The XML looks like this:
# <sequence>
# <int>792134D9B4AD82D5431ED03835A88E2596EB35E5B13054BD9B05A0069281ACC9</int>
# <int>481E758CC1E3CBF825537EC3D9A2CA627E5FAD1137BBEA65DF38658DCB0A9ED5</int>
# </sequence>

# Copy raw R and S hex values into a Chilkat BinData object.
$bd = chilkat::CkBinData->new();
$r = $xml->getChildContent("int[0]");
$s = $xml->getChildContent("int[1]");
$bd->AppendEncoded($r,"hex");
$bd->AppendEncoded($s,"hex");

print "Number of bytes in bd: " . $bd->get_NumBytes() . "\r\n";