(C# UWP/WinRT) ECDSA Sign and Verify

Demonstrates how to create an ECDSA signature on the SHA256 hash of some data, and then verify.

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

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

// First load an ECDSA private key to be used for signing.
Chilkat.PrivateKey privKey = new Chilkat.PrivateKey();
bool success = privKey.LoadEncryptedPemFile("qa_data/ecc/secp256r1-key-pkcs8-secret.pem","secret");
if (success == false) {
    Debug.WriteLine(privKey.LastErrorText);
    return;
}

// Sign the SHA256 hash of some data.
Chilkat.BinData bd = new Chilkat.BinData();
success = bd.LoadFile("qa_data/hamlet.xml");
if (success == false) {
    Debug.WriteLine("Failed to load file to be hashed.");
    return;
}

Chilkat.Crypt2 crypt = new Chilkat.Crypt2();
crypt.HashAlgorithm = "sha256";
crypt.EncodingMode = "base64";
string hashStr = crypt.HashBdENC(bd);

Chilkat.Ecc ecdsa = new Chilkat.Ecc();
Chilkat.Prng prng = new Chilkat.Prng();
// Returns ASN.1 signature as a base64 string.
string sig = ecdsa.SignHashENC(hashStr,"base64",privKey,prng);
Debug.WriteLine("sig = " + sig);

// The signature is in ASN.1 format (which may be described as the "encoded DSS signature").
// SEQUENCE (2 elem)
//   INTEGER (255 bit) 4849395540832462044300553275435608522154141569743642905628579547100940...
//   INTEGER (255 bit) 3680701124244788134409868118208591399799457104230118295614152238560005...

// If you wish, you can get the r and s components of the signature like this:
Chilkat.Asn asn = new Chilkat.Asn();
asn.LoadEncoded(sig,"base64");
Chilkat.Xml xml = new Chilkat.Xml();
xml.LoadXml(asn.AsnToXml());

Debug.WriteLine(xml.GetXml());

// We now have this:
// <?xml version="1.0" encoding="utf-8"?>
// <sequence>
//     <int>6650D422D86BA4A228B5617604E59052591B9B2C32EF324C44D09EF67E5F0060</int>
//     <int>0CFD9F6AC85042FC70F672C141BA6B2A4CAFBB906C3D907BCCC1BED62B28326F</int>
// </sequence>

// Get the "r" and "s" as hex strings
string r = xml.GetChildContentByIndex(0);
string s = xml.GetChildContentByIndex(1);

Debug.WriteLine("r = " + r);
Debug.WriteLine("s = " + s);

// --------------------------------------------------------------------
// Now verify against the hash of the original data.

// Get the corresponding public key.
Chilkat.PublicKey pubKey = new Chilkat.PublicKey();
success = pubKey.LoadFromFile("qa_data/ecc/secp256r1-pub.pem");
if (success == false) {
    Debug.WriteLine(pubKey.LastErrorText);
    return;
}

// We already have the SHA256 hash of the original data (hashStr) so no need to re-do it..
Chilkat.Ecc ecc2 = new Chilkat.Ecc();
int result = ecc2.VerifyHashENC(hashStr,sig,"base64",pubKey);
if (result != 1) {
    Debug.WriteLine(ecc2.LastErrorText);
    return;
}

Debug.WriteLine("Verified!");

// Note: If we have only r,s and wish to reconstruct the ASN.1 signature, we do it like this:
Chilkat.Xml xml2 = new Chilkat.Xml();
xml2.Tag = "sequence";
xml2.NewChild2("int",r);
xml2.NewChild2("int",s);

Chilkat.Asn asn2 = new Chilkat.Asn();
asn2.LoadAsnXml(xml2.GetXml());
string encodedSig = asn2.GetEncodedDer("base64");
Debug.WriteLine("encoded DSS signature: " + encodedSig);

// You can go to https://lapo.it/asn1js/  and copy/paste the base64 encodedSig into the online tool, then press the "decode" button.
// You will see the ASN.1 such as this:

// SEQUENCE (2 elem)
//   INTEGER (255 bit) 4849395540832462044300553275435608522154141569743642905628579547100940...
//   INTEGER (255 bit) 3680701124244788134409868118208591399799457104230118295614152238560005...