(C# UWP/WinRT) Validate a JWS Using ECDSA P-521 SHA-512

Validates a JSON Web Signature (JWS) that uses ECDSA P-521 SHA-512

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.

// This example takes a JSON signature in compact serialization format,
// and uses an ECDSA public key to validate and recover the protected header and payload.

// We only need a public key for signature validation.  This is the ECDSA public key
// that is used:

//      {"kty":"EC", 
//       "crv":"P-521", 
//       "x":"AekpBQ8ST8a8VcfVOTNl353vSrDCLLJXmPk06wTjxrrjcBpXp5EOnYG_NjFZ6OvLFV1jSfS9tsz4qUxcWceqwQGk", 
//       "y":"ADSmRA43Z1DSNx_RvcLI87cdL07l6jQyyBXMoxVg_l2Th-x3S1WDhjDly79ajL4Kkd0AZMaZmh9ubmf63e3kyMj2" 
//      } 

Chilkat.StringBuilder sbPubKey = new Chilkat.StringBuilder();
sbPubKey.Append("{\"kty\":\"EC\",");
sbPubKey.Append("\"crv\":\"P-521\",");
sbPubKey.Append("\"x\":\"AekpBQ8ST8a8VcfVOTNl353vSrDCLLJXmPk06wTjxrrjcBpXp5EOnYG_NjFZ6OvLFV1jSfS9tsz4qUxcWceqwQGk\",");
sbPubKey.Append("\"y\":\"ADSmRA43Z1DSNx_RvcLI87cdL07l6jQyyBXMoxVg_l2Th-x3S1WDhjDly79ajL4Kkd0AZMaZmh9ubmf63e3kyMj2\"");
sbPubKey.Append("}");

Chilkat.PublicKey pubKey = new Chilkat.PublicKey();
bool success = pubKey.LoadFromString(sbPubKey.GetAsString());
if (success != true) {
    Debug.WriteLine(pubKey.LastErrorText);
    return;
}

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

// Set the ECC public key:
int signatureIndex = 0;
jws.SetPublicKey(signatureIndex,pubKey);

// Load the JWS.
Chilkat.StringBuilder sbJws = new Chilkat.StringBuilder();
sbJws.Append("eyJhbGciOiJFUzUxMiJ9");
sbJws.Append(".");
sbJws.Append("UGF5bG9hZA");
sbJws.Append(".");
sbJws.Append("AdwMgeerwtHoh-l192l60hp9wAHZFVJbLfD_UxMi70cwnZOYaRI1bKPWROc-mZZq");
sbJws.Append("wqT2SI-KGDKB34XO0aw_7XdtAG8GaSwFKdCAPZgoXD2YBJZCPEX3xKpRwcdOO8Kp");
sbJws.Append("EHwJjyqOgzDO7iKvU8vcnwNrmxYbSW9ERBXukOXolLzeO_Jn");

success = jws.LoadJwsSb(sbJws);
if (success != true) {
    Debug.WriteLine(jws.LastErrorText);
    return;
}

// Validate the 1st (and only) signature at index 0..
int v = jws.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(jws.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.");
Debug.WriteLine("--");

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

// Examine the protected header:
Chilkat.JsonObject joseHeader = jws.GetProtectedHeader(signatureIndex);
if (jws.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:
// (the string "Payload" was the content that was signed.)

// 	Signature validated.
// 	--
// 	Recovered content:
// 	Payload
// 	--
// 	Protected (JOSE) header:
// 	{
// 	  "alg": "ES512"
// 	}