(MFC) Validate a JWS Using ECDSA P-256 SHA-256

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 C/C++ Library Downloads MS Visual C/C++ Libs

See Also: Using MFC CString in Chilkat

#include <CkStringBuilder.h>
#include <CkPublicKey.h>
#include <CkJws.h>
#include <CkJsonObject.h>

void ChilkatSample(void)
    {
    CkString strOut;

    // 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-256", 
    //       "x":"f83OJ3D2xF1Bg8vub9tLe1gHMzV76e8Tus9uPHvRVEU", 
    //       "y":"x_FEzRu9m36HLN_tue659LNpXW6pCyStikYjKIWI5a0" 
    //      } 

    CkStringBuilder sbPubKey;
    sbPubKey.Append("{\"kty\":\"EC\",");
    sbPubKey.Append("\"crv\":\"P-256\",");
    sbPubKey.Append("\"x\":\"f83OJ3D2xF1Bg8vub9tLe1gHMzV76e8Tus9uPHvRVEU\",");
    sbPubKey.Append("\"y\":\"x_FEzRu9m36HLN_tue659LNpXW6pCyStikYjKIWI5a0\"");
    sbPubKey.Append("}");

    CkPublicKey pubKey;
    bool success = pubKey.LoadFromString(sbPubKey.getAsString());
    if (success != true) {
        strOut.append(pubKey.lastErrorText());
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    CkJws jws;

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

    // Load the JWS.
    CkStringBuilder sbJws;
    sbJws.Append("eyJhbGciOiJFUzI1NiJ9");
    sbJws.Append(".");
    sbJws.Append("eyJpc3MiOiJqb2UiLA0KICJleHAiOjEzMDA4MTkzODAsDQogImh0dHA6Ly9leGFt");
    sbJws.Append("cGxlLmNvbS9pc19yb290Ijp0cnVlfQ");
    sbJws.Append(".");
    sbJws.Append("DtEhU3ljbEg8L38VWAfUAqOyKAM6-Xx-F4GawxaepmXFCgfTjDxw5djxLa8ISlSA");
    sbJws.Append("pmWQxfKTUJqPP3-Kg6NU1Q");

    success = jws.LoadJwsSb(sbJws);
    if (success != true) {
        strOut.append(jws.lastErrorText());
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        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..
        strOut.append("Method call failed for some other reason.");
        strOut.append("\r\n");
        strOut.append(jws.lastErrorText());
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    if (v == 0) {
        strOut.append("Invalid signature.  The ECC key was incorrect, the JWS was invalid, or both.");
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    // If we get here, the signature was validated..
    strOut.append("Signature validated.");
    strOut.append("\r\n");
    strOut.append("--");
    strOut.append("\r\n");

    // Recover the original content:
    strOut.append("Recovered content:");
    strOut.append("\r\n");
    strOut.append(jws.getPayload("utf-8"));
    strOut.append("\r\n");
    strOut.append("--");
    strOut.append("\r\n");

    // Examine the protected header:
    CkJsonObject *joseHeader = jws.GetProtectedHeader(signatureIndex);
    if (jws.get_LastMethodSuccess() != true) {
        strOut.append("No protected header found at the given index.");
        strOut.append("\r\n");
        SetDlgItemText(IDC_EDIT1,strOut.getUnicode());
        return;
    }

    joseHeader->put_EmitCompact(false);

    strOut.append("Protected (JOSE) header:");
    strOut.append("\r\n");
    strOut.append(joseHeader->emit());
    strOut.append("\r\n");
    delete joseHeader;

    // Output:

    // 	Signature validated.
    // 	--
    // 	Recovered content:
    // 	{"iss":"joe",
    // 	 "exp":1300819380,
    // 	 "http://example.com/is_root":true}
    // 	--
    // 	Protected (JOSE) header:
    // 	{ 
    // 	  "alg": "ES256"
    // 	}


    SetDlgItemText(IDC_EDIT1,strOut.getUnicode());

    }