(C# UWP/WinRT) Create a JWS Using ECDSA P-256 SHA-256

Creates and validates a JSON Web Signature (JWS) that uses ECDSA P-256 SHA-256

Note: This example requires Chilkat v9.5.0.66 or greater.

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

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

// Note: This example requires Chilkat v9.5.0.66 or greater.

// Use the following ECC key loaded from JWK format.
Chilkat.StringBuilder sbJwk = new Chilkat.StringBuilder();
sbJwk.Append("{\"kty\":\"EC\",");
sbJwk.Append("\"crv\":\"P-256\",");
sbJwk.Append("\"x\":\"f83OJ3D2xF1Bg8vub9tLe1gHMzV76e8Tus9uPHvRVEU\",");
sbJwk.Append("\"y\":\"x_FEzRu9m36HLN_tue659LNpXW6pCyStikYjKIWI5a0\",");
sbJwk.Append("\"d\":\"jpsQnnGQmL-YBIffH1136cspYG6-0iY7X1fCE9-E9LI\"");
sbJwk.Append("}");

Chilkat.PrivateKey eccKey = new Chilkat.PrivateKey();
// Note: This example loads the ECDSA key from JWK format.  Any format can be loaded
// into the private key object. (See the online reference documentation..)
bool success = eccKey.LoadJwk(sbJwk.GetAsString());
if (success != true) {
    Debug.WriteLine(eccKey.LastErrorText);
    return;
}

// Create the JWS Protected Header
Chilkat.JsonObject jwsProtHdr = new Chilkat.JsonObject();
jwsProtHdr.AppendString("alg","ES256");

Chilkat.Jws jws = new Chilkat.Jws();

// Set the protected header:
int signatureIndex = 0;
jws.SetProtectedHeader(signatureIndex,jwsProtHdr);

// Set the ECC key:
jws.SetPrivateKey(signatureIndex,eccKey);

// Set the payload.
bool bIncludeBom = false;
string payloadStr = "In our village, folks say God crumbles up the old moon into stars.";
jws.SetPayload(payloadStr,"utf-8",bIncludeBom);

// Create the JWS
// By default, the compact serialization is used.
string jwsCompact = jws.CreateJws();
if (jws.LastMethodSuccess != true) {
    Debug.WriteLine(jws.LastErrorText);
    return;
}

Debug.WriteLine("JWS: " + jwsCompact);

// Note: ECC signatures use random values, so the output will be different each time a signature is produced.
// sample output:
// JWS: eyJhbGciOiJFUzI1NiJ9.SW4gb3VyIHZpbGxhZ2UsIGZvbGtzIHNheSBHb2QgY3J1bWJsZXMgdXAgdGhlIG9sZCBtb29uIGludG8gc3RhcnMu.J6EGTNkeuEjehHHBu0SOKzifm8r35wbx49A5964pxzB7gannyZZPMkK7vmlaPJ-K8Xmm8cZsQySAPC12Xd8avw

// Now load the JWS, validate, and recover the original text.
Chilkat.Jws jws2 = new Chilkat.Jws();

// Load the JWS.
success = jws2.LoadJws(jwsCompact);

Chilkat.PublicKey eccPubKey = eccKey.GetPublicKey();

// Set the ECC public key used for validation.
signatureIndex = 0;
jws2.SetPublicKey(signatureIndex,eccPubKey);

// Validate the 1st (and only) signature at index 0..
int v = jws2.Validate(signatureIndex);
if (v < 0) {
    // Perhaps Chilkat was not unlocked or the trial expired..
    Debug.WriteLine("Method call failed for some other reason.");
    Debug.WriteLine(jws2.LastErrorText);
    return;
}

if (v == 0) {
    Debug.WriteLine("Invalid signature.  The ECC key was incorrect, the JWS was invalid, or both.");
    return;
}

// If we get here, the signature was validated..
Debug.WriteLine("Signature validated.");

// Recover the original content:
Debug.WriteLine(jws2.GetPayload("utf-8"));

// Examine the protected header:
Chilkat.JsonObject joseHeader = jws2.GetProtectedHeader(signatureIndex);
if (jws2.LastMethodSuccess != true) {
    Debug.WriteLine("No protected header found at the given index.");
    return;
}

joseHeader.EmitCompact = false;

Debug.WriteLine("Protected (JOSE) header:");
Debug.WriteLine(joseHeader.Emit());

// Output:

// Signature validated.
// In our village, folks say God crumbles up the old moon into stars.
// Protected (JOSE) header:
// { 
//   "alg": "ES256"
// }