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

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

Features

• Envelope
  • Sender
  • Receiver
  • Time (same value from content.time)
• Content
  • Type
  • Serial Number
  • Time
  • Group (Optional)
• Message
  • Instant Message
  • Secure Message
  • Reliable Message

Envelope

Message Envelope

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

Content

/* example */
{
    "type"     : "1",       // message type
    "sn"       : 412968873, // serial number (message ID in conversation)
    
    "text"     : "Hey guy!"
}

Content Type

FOUNDATION_EXPORT NSString * DKDContentType_Any;      // 0x00: 0000 0000 (Undefined)

FOUNDATION_EXPORT NSString * DKDContentType_Text;     // 0x01: 0000 0001

FOUNDATION_EXPORT NSString * DKDContentType_File;     // 0x10: 0001 0000
FOUNDATION_EXPORT NSString * DKDContentType_Image;    // 0x12: 0001 0010
FOUNDATION_EXPORT NSString * DKDContentType_Audio;    // 0x14: 0001 0100
FOUNDATION_EXPORT NSString * DKDContentType_Video;    // 0x16: 0001 0110

// Web Page
FOUNDATION_EXPORT NSString * DKDContentType_Page;     // 0x20: 0010 0000

// Name Card
FOUNDATION_EXPORT NSString * DKDContentType_NameCard; // 0x33: 0011 0011

// Quote a message before and reply it with text
FOUNDATION_EXPORT NSString * DKDContentType_Quote;    // 0x37: 0011 0111

FOUNDATION_EXPORT NSString * DKDContentType_Money;        // 0x40: 0100 0000
FOUNDATION_EXPORT NSString * DKDContentType_Transfer;     // 0x41: 0100 0001
FOUNDATION_EXPORT NSString * DKDContentType_LuckyMoney;   // 0x42: 0100 0010
FOUNDATION_EXPORT NSString * DKDContentType_ClaimPayment; // 0x48: 0100 1000 (Claim for Payment)
FOUNDATION_EXPORT NSString * DKDContentType_SplitBill;    // 0x49: 0100 1001 (Split the Bill)

FOUNDATION_EXPORT NSString * DKDContentType_Command;      // 0x88: 1000 1000
FOUNDATION_EXPORT NSString * DKDContentType_History;      // 0x89: 1000 1001 (Entity History Command)

// Application Customized
FOUNDATION_EXPORT NSString * DKDContentType_Application;      // 0xA0: 1010 0000 (Aoplication 0nly, Reserved)
//FOUNDATION_EXPORT NSString * DKDContentType_Application_1;  // 0xA1: 1010 0001 (Reserved)
//                             ...                            //       1010 ???? (Reserved)
//FOUNDATION_EXPORT NSString * DKDContentType_Application_15; // 0xAF: 1010 1111 (Reserved)

//FOUNDATION_EXPORT NSString * DKDContentType_Customized_0;   // 0xC0: 1100 0000 (Reserved)
//FOUNDATION_EXPORT NSString * DKDContentType_Customized_1;   // 0xC1: 1100 0001 (Reserved)
//                           .....                            //       1100 ???? (Reserved)
FOUNDATION_EXPORT NSString * DKDContentType_Array;            // 0xCA: 1100 1010 (Content Array)
//                           ...                              //       1100 ???? (Reserved)
FOUNDATION_EXPORT NSString * DKDContentType_Customized;       // 0xCC: 1100 1100 (Customized Content)
//                           ...                              //       1100 ???? (Reserved)
FOUNDATION_EXPORT NSString * DKDContentType_CombineForward;   // 0xCF: 1100 1111 (Combine and Forward)

// Top-Secret message forward by proxy (MTA)
FOUNDATION_EXPORT NSString * DKDContentType_Forward;          // 0xFF: 1111 1111

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" : "1",       // 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)

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