(C# UWP/WinRT) ECDSA Sign Data and Get Raw R and S Values

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

Chilkat Universal Windows Platform (UWP) / WinRT Downloads Chilkat for the Universal Windows Platform (UWP)

// 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.

Chilkat.Crypt2 crypt = new Chilkat.Crypt2();
crypt.HashAlgorithm = "SHA256";
crypt.Charset = "utf-8";
crypt.EncodingMode = "base64";

// Hash a string.
string hash1 = crypt.HashStringENC("The quick brown fox jumps over the lazy dog");
Debug.WriteLine("hash1 = " + hash1);

// -----------------------------------------------------------
// 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-----

Chilkat.PrivateKey privKey = new Chilkat.PrivateKey();
bool success = privKey.LoadPemFile("qa_data/ecc/secp256r1-key-pkcs8.pem");
if (success != true) {
    Debug.WriteLine(privKey.LastErrorText);
    return;
}

// Sign the hash..
Chilkat.Prng prng = new Chilkat.Prng();
Chilkat.Ecc ecdsa = new Chilkat.Ecc();
string ecdsaSigBase64 = ecdsa.SignHashENC(hash1,"base64",privKey,prng);
if (ecdsa.LastMethodSuccess != true) {
    Debug.WriteLine(ecdsa.LastErrorText);
    return;
}

// 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

Debug.WriteLine("Base64 ECDSA signature = " + ecdsaSigBase64);

// If the raw R and S values are needed, here's how to get them:
Chilkat.Asn asn = new Chilkat.Asn();
success = asn.LoadEncoded(ecdsaSigBase64,"base64");
if (success == false) {
    Debug.WriteLine(asn.LastErrorText);
    return;
}

// The R and X will be in hexidecimal in the XML.
Chilkat.Xml xml = new Chilkat.Xml();
xml.LoadXml(asn.AsnToXml());
Debug.WriteLine(xml.GetXml());

// 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.
Chilkat.BinData bd = new Chilkat.BinData();
string r = xml.GetChildContent("int[0]");
string s = xml.GetChildContent("int[1]");
bd.AppendEncoded(r,"hex");
bd.AppendEncoded(s,"hex");

Debug.WriteLine("Number of bytes in bd: " + Convert.ToString(bd.NumBytes));