(Swift 3,4,5...) JWE Using Flattened JWE JSON Serialization

This example duplicates the example A.5 in RFC 7516 for JSON Web Encryption (JWE).

This example demonstrates using the flattened JWE JSON Serialization syntax. This example demonstrates the capability for encrypting the plaintext to a single recipient in a flattened JSON structure.

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: {"enc":"A128CBC-HS256"}
    let jweProtHdr = CkoJsonObject()!
    jweProtHdr.append("enc", value: "A128CBC-HS256")
    jwe.setProtectedHeader(jweProtHdr)

    // We have a single recipient that uses AES Key Wrap to encrypt the CEK.
    // 
    //      {"alg":"A128KW","kid":"7"}

    let jweRecipientHdr = CkoJsonObject()!
    jweRecipientHdr.append("alg", value: "A128KW")
    jweRecipientHdr.append("kid", value: "7")
    var recipientIndex: Int = 0
    jwe.setRecipientHeader(recipientIndex, json: jweRecipientHdr)

    // Set the Shared Unprotected Header:  {"jku":"https://server.example.com/keys.jwks"}
    let jweUnprotHdr = CkoJsonObject()!
    jweUnprotHdr.append("jku", value: "https://server.example.com/keys.jwks")
    jwe.setUnprotectedHeader(jweUnprotHdr)

    // Set the AES key wrapping key.
    var aesWrappingKey: String? = "GawgguFyGrWKav7AX4VKUg"
    recipientIndex = 0
    jwe.setWrappingKey(recipientIndex, encodedKey: aesWrappingKey, encoding: "base64url")

    // OK.. everything has been specified.
    // Now encrypt.  
    // Indicate that we prefer the flattened JSON serialization.
    jwe.preferFlattened = true
    var strJwe: String? = jwe.encrypt(plaintext, charset: "utf-8")
    if jwe.lastMethodSuccess != true {
        print("\(jwe.lastErrorText!)")
        return
    }

    // The JWE is produced in the most compact form possible (a single line).
    // Let's load it into a JSON object and examine in a non-compact pretty-printed format:
    let jsonTemp = CkoJsonObject()!
    jsonTemp.load(strJwe)
    jsonTemp.emitCompact = false
    print("\(jsonTemp.emit()!)")

    // The JWE looks like this:
    // (Note: Because of random values used in the encryption process, your encrypted results will be different.)

    // 	{ 
    // 	  "protected": "eyJlbmMiOiJBMTI4Q0JDLUhTMjU2In0",
    // 	  "unprotected": { 
    // 	    "jku": "https://server.example.com/keys.jwks"
    // 	  },
    // 	  "header": { 
    // 	    "alg": "A128KW",
    // 	    "kid": "7"
    // 	  },
    // 	  "encrypted_key": "FW7z9VxOvnF2ClicvUT4HTeqcdyh90C6qytfEFJsOb77FOwTfYrc3w",
    // 	  "iv": "O6Ly5-eML3zTs-_fNX3D5Q",
    // 	  "ciphertext": "Q8NLmeac9JhLh0CQPuG_7D9wVDb55eToCh0g5-FQ4M0",
    // 	  "tag": "slzlo6-J9C7wSDF4dh_kBg"
    // 	} 

    // Now decrypt......................................

    // First, load the JWE..
    let jwe2 = CkoJwe()!
    success = jwe2.load(strJwe)
    if success != true {
        print("\(jwe2.lastErrorText!)")
        return
    }

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

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

    print("original text decrypted with AES key wrap key: ")
    print("\(originalPlaintext!)")

    // ---------------------------------------------------------------------------------
    // It should also be possible to decrypt the flattened JWE as shown in RFC 7516, Appendix A.5
    // because it was produced using the same key.

    let sbJwe = CkoStringBuilder()!

    sbJwe.append("{")
    sbJwe.append("\"protected\":")
    sbJwe.append("\"eyJlbmMiOiJBMTI4Q0JDLUhTMjU2In0\",")
    sbJwe.append("\"unprotected\":")
    sbJwe.append("{\"jku\":\"https://server.example.com/keys.jwks\"},")
    sbJwe.append("\"header\":")
    sbJwe.append("{\"alg\":\"A128KW\",\"kid\":\"7\"},")
    sbJwe.append("\"encrypted_key\":")
    sbJwe.append("\"6KB707dM9YTIgHtLvtgWQ8mKwboJW3of9locizkDTHzBC2IlrT1oOQ\",")
    sbJwe.append("\"iv\":")
    sbJwe.append("\"AxY8DCtDaGlsbGljb3RoZQ\",")
    sbJwe.append("\"ciphertext\":")
    sbJwe.append("\"KDlTtXchhZTGufMYmOYGS4HffxPSUrfmqCHXaI9wOGY\",")
    sbJwe.append("\"tag\":")
    sbJwe.append("\"Mz-VPPyU4RlcuYv1IwIvzw\"")
    sbJwe.append("}")

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

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

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

    print("original text decrypted from published flattened JWE: ")
    print("\(originalPlaintext!)")

    // The output:

    // original text decrypted with AES key wrap key: 
    // Live long and prosper.
    // original text decrypted from published flattened JWE: 
    // Live long and prosper.

}