(Swift 3,4,5...) 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.

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func chilkatTest() {
    // 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.
    let sbJwk = CkoStringBuilder()!
    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("}")

    let eccKey = CkoPrivateKey()!
    // 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..)
    var success: Bool = eccKey.loadJwk(sbJwk.getAsString())
    if success != true {
        print("\(eccKey.lastErrorText!)")
        return
    }

    // Create the JWS Protected Header
    let jwsProtHdr = CkoJsonObject()!
    jwsProtHdr.append("alg", value: "ES256")

    let jws = CkoJws()!

    // Set the protected header:
    var signatureIndex: Int = 0
    jws.setProtectedHeader(signatureIndex, json: jwsProtHdr)

    // Set the ECC key:
    jws.setPrivateKey(signatureIndex, privKey: eccKey)

    // Set the payload.
    var bIncludeBom: Bool = false
    var payloadStr: String? = "In our village, folks say God crumbles up the old moon into stars."
    jws.setPayload(payloadStr, charset: "utf-8", includeBom: bIncludeBom)

    // Create the JWS
    // By default, the compact serialization is used.
    var jwsCompact: String? = jws.createJws()
    if jws.lastMethodSuccess != true {
        print("\(jws.lastErrorText!)")
        return
    }

    print("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.
    let jws2 = CkoJws()!

    // Load the JWS.
    success = jws2.load(jwsCompact)

    var eccPubKey: CkoPublicKey? = eccKey.getPublicKey()

    // Set the ECC public key used for validation.
    signatureIndex = 0
    jws2.setPublicKey(signatureIndex, pubKey: eccPubKey)
    eccPubKey = nil

    // Validate the 1st (and only) signature at index 0..
    var v: Int = jws2.validate(signatureIndex).intValue
    if v < 0 {
        // Perhaps Chilkat was not unlocked or the trial expired..
        print("Method call failed for some other reason.")
        print("\(jws2.lastErrorText!)")
        return
    }

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

    // If we get here, the signature was validated..
    print("Signature validated.")

    // Recover the original content:
    print("\(jws2.getPayload("utf-8")!)")

    // Examine the protected header:
    var joseHeader: CkoJsonObject? = jws2.getProtectedHeader(signatureIndex)
    if jws2.lastMethodSuccess != true {
        print("No protected header found at the given index.")
        return
    }

    joseHeader.emitCompact = false

    print("Protected (JOSE) header:")
    print("\(joseHeader!.emit()!)")
    joseHeader = nil

    // Output:

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

}