Dao Ke Dao (道可道) -- Message Module (Objective-C)

This document introduces a common Message Module for decentralized instant messaging.

Copyright © 2018-2019 Albert Moky

• Envelope
  • Sender
  • Receiver
  • Time
• Content
  • Type
  • Serial Number
• Message
  • Instant Message
  • Secure Message
  • Reliable Message

0. Envelope

Message Envelope

/* example */
{
    sender   : "moki@4WDfe3zZ4T7opFSi3iDAKiuTnUHjxmXekk",
    receiver : "hulk@4YeVEN3aUnvC1DNUufCq1bs9zoBSJTzVEj",
    time     : 1545405083
}

1. Content

/* example */
{
    type     : 0x01,      // message type
    sn       : 412968873, // serial number (message ID in conversation)
    
    text     : "Hey guy!"
}

Message Content Type

typedef NS_ENUM(UInt8, DKDContentType) {
    DKDContentType_Unknown    = 0x00,
    
    DKDContentType_Text       = 0x01, // 0000 0001
    
    DKDContentType_File       = 0x10, // 0001 0000
    DKDContentType_Image      = 0x12, // 0001 0010
    DKDContentType_Audio      = 0x14, // 0001 0100
    DKDContentType_Video      = 0x16, // 0001 0110
    
    DKDContentType_Page       = 0x20, // 0010 0000
    
    // quote a message before and reply it with text
    DKDContentType_Quote      = 0x37, // 0011 0111
    
    DKDContentType_Money      = 0x40, // 0100 0000
//    DKDContentType_LuckyMoney = 0x41, // 0100 0001
//    DKDContentType_Transfer   = 0x42, // 0100 0010

    DKDContentType_Command    = 0x88, // 1000 1000
    DKDContentType_History    = 0x89, // 1000 1001 (Entity history command)
    
    // top-secret message forward by proxy (Service Provider)
    DKDContentType_Forward    = 0xFF  // 1111 1111
};

2. Message

When the user want to send out a message, the client needs TWO steps before sending it:

1. Encrypt the Instant Message to Secure Message;
2. Sign the Secure Message to Reliable Message.

Accordingly, when the client received a message, it needs TWO steps to extract the content:

1. Verify the Reliable Message to Secure Message;
2. Decrypt the Secure Message to Instant Message.

    Message Transforming
    ~~~~~~~~~~~~~~~~~~~~

    Instant Message  <-->  Secure Message  <-->  Reliable Message
    +-------------+        +------------+        +--------------+
    |  sender     |        |  sender    |        |  sender      |
    |  receiver   |        |  receiver  |        |  receiver    |
    |  time       |        |  time      |        |  time        |
    |             |        |            |        |              |
    |  content    |        |  data      |        |  data        |
    +-------------+        |  key/keys  |        |  key/keys    |
                           +------------+        |  signature   |
                                                 +--------------+
    Algorithm:
        data      = password.encrypt(content)
        key       = receiver.public_key.encrypt(password)
        signature = sender.private_key.sign(data)

Instant Message

/* example */
{
    //-------- head (envelope) --------
    sender   : "moki@4WDfe3zZ4T7opFSi3iDAKiuTnUHjxmXekk",
    receiver : "hulk@4YeVEN3aUnvC1DNUufCq1bs9zoBSJTzVEj",
    time     : 1545405083,
    
    //-------- body (content) ---------
    content  : {
        type : 0x01,      // message type
        sn   : 412968873, // serial number (ID)
        text : "Hey guy!"
    }
}

content -> JsON string: {"sn":412968873,"text":"Hey guy!","type":1}

Secure Message

/**
 *  Algorithm:
 *      string = json(content);
 *      PW     = random();
 *      data   = encrpyt(string, PW);      // Symmetric
 *      key    = encrypt(PW, receiver.PK); // Asymmetric
 */
{
    //-------- head (envelope) --------
    sender   : "moki@4WDfe3zZ4T7opFSi3iDAKiuTnUHjxmXekk",
    receiver : "hulk@4YeVEN3aUnvC1DNUufCq1bs9zoBSJTzVEj",
    time     : 1545405083,
    
    //-------- body (content) ---------
    data     : "9cjCKG99ULCCxbL2mkc/MgF1saeRqJaCc+S12+HCqmsuF7TWK61EwTQWZSKskUeF",
    key      : "WH/wAcu+HfpaLq+vRblNnYufkyjTm4FgYyzW3wBDeRtXs1TeDmRxKVu7nQI/sdIALGLXrY+O5mlRfhU8f8TuIBilZUlX/eIUpL4uSDYKVLaRG9pOcrCHKevjUpId9x/8KBEiMIL5LB0Vo7sKrvrqosCnIgNfHbXMKvMzwcqZEU8="
}

Reliable Message

/**
 *  Algorithm:
 *      signature = sign(data, sender.SK);
 */
{
    //-------- head (envelope) --------
    sender   : "moki@4WDfe3zZ4T7opFSi3iDAKiuTnUHjxmXekk",
    receiver : "hulk@4YeVEN3aUnvC1DNUufCq1bs9zoBSJTzVEj",
    time     : 1545405083,
    
    //-------- body (content) ---------
    data      : "9cjCKG99ULCCxbL2mkc/MgF1saeRqJaCc+S12+HCqmsuF7TWK61EwTQWZSKskUeF",
    key       : "WH/wAcu+HfpaLq+vRblNnYufkyjTm4FgYyzW3wBDeRtXs1TeDmRxKVu7nQI/sdIALGLXrY+O5mlRfhU8f8TuIBilZUlX/eIUpL4uSDYKVLaRG9pOcrCHKevjUpId9x/8KBEiMIL5LB0Vo7sKrvrqosCnIgNfHbXMKvMzwcqZEU8=",
    signature : "Yo+hchWsQlWHtc8iMGS7jpn/i9pOLNq0E3dTNsx80QdBboTLeKoJYAg/lI+kZL+g7oWJYpD4qKemOwzI+9pxdMuZmPycG+0/VM3HVSMcguEOqOH9SElp/fYVnm4aSjAJk2vBpARzMT0aRNp/jTFLawmMDuIlgWhBfXvH7bT7rDI="
}

(All data encode with BASE64 algorithm as default)