(Swift 3,4,5...) JWE using AES Key Wrap and AES_128_CBC_HMAC_SHA_256

This example duplicates the example A.3 in RFC 7516 for JSON Web Encryption (JWE).

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.

    var success: Bool
    var plaintext: String? = "Live long and prosper."

    let jwe = CkoJwe()!

    // First build the JWE Protected Header: {"alg":"A128KW","enc":"A128CBC-HS256"}
    let jweProtHdr = CkoJsonObject()!
    jweProtHdr.append("alg", value: "A128KW")
    jweProtHdr.append("enc", value: "A128CBC-HS256")
    jwe.setProtectedHeader(jweProtHdr)

    print("JWE Protected Header: \(jweProtHdr.emit()!)")
    print("--")

    // The example A.3 in RFC 7516 uses the following 128-bit AES key,
    // specified in JWK (JSON Web Key) format:
    //      {"kty":"oct",
    //       "k":"GawgguFyGrWKav7AX4VKUg"
    //      }
    // This is just a way of saying: The key type ("kty") is 
    // a bunch of octets ("k") in base64url encoding.
    // We can simply set the AES wrapping key like this:
    var aesWrappingKey: String? = "GawgguFyGrWKav7AX4VKUg"
    jwe.setWrappingKey(0, encodedKey: aesWrappingKey, encoding: "base64url")

    // Encrypt and return the JWE:
    var strJwe: String? = jwe.encrypt(plaintext, charset: "utf-8")
    if jwe.lastMethodSuccess != true {
        print("\(jwe.lastErrorText!)")
        return
    }

    // Show the JWE we just created:
    print("\(strJwe!)")

    // Decrypt the JWE that was just produced.
    // 1) Load the JWE.
    // 2) Set the AES wrapping key.
    // 3) Decrypt.
    let jwe2 = CkoJwe()!
    success = jwe2.load(strJwe)
    if success != true {
        print("\(jwe2.lastErrorText!)")
        return
    }

    // Set the AES wrap key.
    jwe2.setWrappingKey(0, encodedKey: aesWrappingKey, encoding: "base64url")

    // Decrypt.
    var originalPlaintext: String? = jwe2.decrypt(0, charset: "utf-8")
    if jwe2.lastMethodSuccess != true {
        print("\(jwe2.lastErrorText!)")
        return
    }

    print("original text: ")
    print("\(originalPlaintext!)")

    // ---------------------------------------------------------------------------------
    // It should also be possible to decrypt the JWE as shown in RFC 7516, Appendix A.3.7
    // because it was produced using the same AES Wrap key.

    let sbJwe = CkoStringBuilder()!
    sbJwe.append("eyJhbGciOiJBMTI4S1ciLCJlbmMiOiJBMTI4Q0JDLUhTMjU2In0.")
    sbJwe.append("6KB707dM9YTIgHtLvtgWQ8mKwboJW3of9locizkDTHzBC2IlrT1oOQ.")
    sbJwe.append("AxY8DCtDaGlsbGljb3RoZQ.")
    sbJwe.append("KDlTtXchhZTGufMYmOYGS4HffxPSUrfmqCHXaI9wOGY.")
    sbJwe.append("U0m_YmjN04DJvceFICbCVQ")

    success = jwe2.loadSb(sbJwe)
    if success != true {
        print("\(jwe2.lastErrorText!)")
        return
    }

    jwe2.setWrappingKey(0, encodedKey: aesWrappingKey, encoding: "base64url")

    // Decrypt.
    originalPlaintext = jwe2.decrypt(0, charset: "utf-8")
    if jwe2.lastMethodSuccess != true {
        print("\(jwe2.lastErrorText!)")
        return
    }

    print("\(originalPlaintext!)")

}