(Swift 3,4,5...) JWE using RSAES-OAEP and AES GCM

This example duplicates the example A.1 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? = "The true sign of intelligence is not knowledge but imagination."

    // ---------------------------------
    // A.1.1 JOSE Header
    // First build the JWE Protected Header.
    // We want to build this: {"alg":"RSA-OAEP","enc":"A256GCM"}
    let jweProtHdr = CkoJsonObject()!
    jweProtHdr.append("alg", value: "RSA-OAEP")
    jweProtHdr.append("enc", value: "A256GCM")
    print("JWE Protected Header: \(jweProtHdr.emit()!)")
    print("--")

    // ---------------------------------
    // A.1.2 Content Encryption Key
    // Note: Chilkat automatically generates the random CEK internally.
    // The application does not need to explicitly take this step.

    // ---------------------------------
    // A.1.3.  Key Encryption
    // The application should load an RSA private key from any format.
    // However, the application does not need to explicitly construct the JWE Encrypted Key.
    // Chilkat automatically does it internally.
    // The design of the Chilkat JWE API is to allow the application to create the JWE
    // after specifying the inputs.  (This is in contrast to forcing the application developer
    // to painstakingly go through each step of the JWE construction process.)

    // The specific RSA key used in the A.1 example is the following JWK:
    let sbJwk = CkoStringBuilder()!
    sbJwk.append("{\"kty\": \"RSA\",")
    sbJwk.append("\"n\": \"oahUIoWw0K0usKNuOR6H4wkf4oBUXHTxRvgb48E-BVvxkeDNjbC4he8rUW")
    sbJwk.append("cJoZmds2h7M70imEVhRU5djINXtqllXI4DFqcI1DgjT9LewND8MW2Krf3S")
    sbJwk.append("psk_ZkoFnilakGygTwpZ3uesH-PFABNIUYpOiN15dsQRkgr0vEhxN92i2a")
    sbJwk.append("sbOenSZeyaxziK72UwxrrKoExv6kc5twXTq4h-QChLOln0_mtUZwfsRaMS")
    sbJwk.append("tPs6mS6XrgxnxbWhojf663tuEQueGC-FCMfra36C9knDFGzKsNa7LZK2dj")
    sbJwk.append("YgyD3JR_MB_4NUJW_TqOQtwHYbxevoJArm-L5StowjzGy-_bq6Gw\",")
    sbJwk.append("\"e\": \"AQAB\",")
    sbJwk.append("\"d\": \"kLdtIj6GbDks_ApCSTYQtelcNttlKiOyPzMrXHeI-yk1F7-kpDxY4-WY5N")
    sbJwk.append("WV5KntaEeXS1j82E375xxhWMHXyvjYecPT9fpwR_M9gV8n9Hrh2anTpTD9")
    sbJwk.append("3Dt62ypW3yDsJzBnTnrYu1iwWRgBKrEYY46qAZIrA2xAwnm2X7uGR1hghk")
    sbJwk.append("qDp0Vqj3kbSCz1XyfCs6_LehBwtxHIyh8Ripy40p24moOAbgxVw3rxT_vl")
    sbJwk.append("t3UVe4WO3JkJOzlpUf-KTVI2Ptgm-dARxTEtE-id-4OJr0h-K-VFs3VSnd")
    sbJwk.append("VTIznSxfyrj8ILL6MG_Uv8YAu7VILSB3lOW085-4qE3DzgrTjgyQ\",")
    sbJwk.append("\"p\": \"1r52Xk46c-LsfB5P442p7atdPUrxQSy4mti_tZI3Mgf2EuFVbUoDBvaRQ-")
    sbJwk.append("SWxkbkmoEzL7JXroSBjSrK3YIQgYdMgyAEPTPjXv_hI2_1eTSPVZfzL0lf")
    sbJwk.append("fNn03IXqWF5MDFuoUYE0hzb2vhrlN_rKrbfDIwUbTrjjgieRbwC6Cl0\",")
    sbJwk.append("\"q\": \"wLb35x7hmQWZsWJmB_vle87ihgZ19S8lBEROLIsZG4ayZVe9Hi9gDVCOBm")
    sbJwk.append("UDdaDYVTSNx_8Fyw1YYa9XGrGnDew00J28cRUoeBB_jKI1oma0Orv1T9aX")
    sbJwk.append("IWxKwd4gvxFImOWr3QRL9KEBRzk2RatUBnmDZJTIAfwTs0g68UZHvtc\",")
    sbJwk.append("\"dp\": \"ZK-YwE7diUh0qR1tR7w8WHtolDx3MZ_OTowiFvgfeQ3SiresXjm9gZ5KL")
    sbJwk.append("hMXvo-uz-KUJWDxS5pFQ_M0evdo1dKiRTjVw_x4NyqyXPM5nULPkcpU827")
    sbJwk.append("rnpZzAJKpdhWAgqrXGKAECQH0Xt4taznjnd_zVpAmZZq60WPMBMfKcuE\",")
    sbJwk.append("\"dq\": \"Dq0gfgJ1DdFGXiLvQEZnuKEN0UUmsJBxkjydc3j4ZYdBiMRAy86x0vHCj")
    sbJwk.append("ywcMlYYg4yoC4YZa9hNVcsjqA3FeiL19rk8g6Qn29Tt0cj8qqyFpz9vNDB")
    sbJwk.append("UfCAiJVeESOjJDZPYHdHY8v1b-o-Z2X5tvLx-TCekf7oxyeKDUqKWjis\",")
    sbJwk.append("\"qi\": \"VIMpMYbPf47dT1w_zDUXfPimsSegnMOA1zTaX7aGk_8urY6R8-ZW1FxU7")
    sbJwk.append("AlWAyLWybqq6t16VFd7hQd0y6flUK4SlOydB61gwanOsXGOAOv82cHq0E3")
    sbJwk.append("eL4HrtZkUuKvnPrMnsUUFlfUdybVzxyjz9JF_XyaY14ardLSjf4L_FNY\"}")

    // Load this JWK into a Chilkat private key object.
    let rsaPrivKey = CkoPrivateKey()!
    success = rsaPrivKey.loadJwk(sbJwk.getAsString())
    if success != true {
        print("\(rsaPrivKey.lastErrorText!)")
        return
    }

    // The public key is used to encrypt (i.e. create the JWE), 
    // and the private key is used to decrypt.
    // The RSA public key is simply a subset of the private key.  The RSA public key
    // is composed of the "n" and "e" members shown above.  These are also known as the
    // modulus and exponent.
    // We can simply get the public key object from the private key object
    var rsaPubKey: CkoPublicKey? = rsaPrivKey.getPublicKey()

    // ---------------------------------
    // A.1.4.  Initialization Vector
    // Chilkat automatically generates the necessary random IV internally.  
    // The application does not need to do this explicitly.

    // ---------------------------------
    // A.1.5.  Additional Authenticated Data
    // The Additional Authenticated Data encryption parameter is
    // ASCII(BASE64URL(UTF8(JWE Protected Header))).
    // Again, Chilkat automatically takes care of this internally.
    // The application does not need to explicitly take this step.

    // ---------------------------------
    // A.1.6.  Content Encryption
    // Again... this step is handled by Chilkat internally.

    // ---------------------------------
    // A.1.7.  Complete Representation
    // The application need only call the Encrypt, EncryptSb, or EncryptBd method
    // return the fully assembled JWE.  
    // The final representation in the Compact Serialization 
    // is the string BASE64URL(UTF8(JWE Protected Header)) || '.' ||
    // BASE64URL(JWE Encrypted Key) || '.' || BASE64URL(JWE Initialization
    // Vector) || '.' || BASE64URL(JWE Ciphertext) || '.' || BASE64URL(JWE
    // Authentication Tag).

    let jwe = CkoJwe()!
    jwe.setProtectedHeader(jweProtHdr)
    jwe.setPublicKey(0, pubKey: rsaPubKey)
    rsaPubKey = nil

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

    // Note: The RSA OAEP algorithm uses random padding bytes internally.
    // Therefore, the results will appear different each time -- even if the
    // identical plaintext is encrypted with the identical RSA key. 
    // (Do not expect the appearance of the results to be the same as what
    // is published in the RFC.  However, what is published in the RFC *should*
    // be decryptable using the code that follows.)
    print("\(strJwe!)")

    // Let's decrypt the JWE that was just produced.
    // Do the following to decrypt a JWE:
    // 1) Load the JWE.
    // 2) Set the private key for decryption.
    // 3) Decrypt.
    let jwe2 = CkoJwe()!
    success = jwe2.load(strJwe)
    if success != true {
        print("\(jwe2.lastErrorText!)")
        return
    }

    // Provide the RSA private key for decryption.
    // (The JWE was encrypted for a single recipient at index 0.)
    jwe2.setPrivateKey(0, privKey: rsaPrivKey)

    // 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.1.7
    // because it was produced using the same RSA key.

    let sbJwe = CkoStringBuilder()!
    sbJwe.append("eyJhbGciOiJSU0EtT0FFUCIsImVuYyI6IkEyNTZHQ00ifQ.")
    sbJwe.append("OKOawDo13gRp2ojaHV7LFpZcgV7T6DVZKTyKOMTYUmKoTCVJRgckCL9kiMT03JGe")
    sbJwe.append("ipsEdY3mx_etLbbWSrFr05kLzcSr4qKAq7YN7e9jwQRb23nfa6c9d-StnImGyFDb")
    sbJwe.append("Sv04uVuxIp5Zms1gNxKKK2Da14B8S4rzVRltdYwam_lDp5XnZAYpQdb76FdIKLaV")
    sbJwe.append("mqgfwX7XWRxv2322i-vDxRfqNzo_tETKzpVLzfiwQyeyPGLBIO56YJ7eObdv0je8")
    sbJwe.append("1860ppamavo35UgoRdbYaBcoh9QcfylQr66oc6vFWXRcZ_ZT2LawVCWTIy3brGPi")
    sbJwe.append("6UklfCpIMfIjf7iGdXKHzg.")
    sbJwe.append("48V1_ALb6US04U3b.")
    sbJwe.append("5eym8TW_c8SuK0ltJ3rpYIzOeDQz7TALvtu6UG9oMo4vpzs9tX_EFShS8iB7j6ji")
    sbJwe.append("SdiwkIr3ajwQzaBtQD_A.")
    sbJwe.append("XFBoMYUZodetZdvTiFvSkQ")

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

    // Provide the RSA private key for decryption.
    jwe2.setPrivateKey(0, privKey: rsaPrivKey)

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

    print("\(originalPlaintext!)")

}