Secure Messaging With Ethereum

Reasoning about Ethereum's Role

Presented by: Cayman Nava (caymannava@gmail.com)

Outline

• Messaging Requirements
• Ethereum's Role
• Message Storage
• Examples
  
• Rendezvous Point
• Interlude - WebRTC
  
• Examples
  

Messaging Requirements

• What kind of messages?
• Voice/Video
• Picture/Text
• Who can read the messages?
• One-on-one (ex: text message)
  
• Group-messaging (ex: Google hangouts)
• Broadcast messaging (ex: Reddit)
• How are the messages stored and transported?
• Synchronous communication - messages sent to online parties
• Asynchronous communication - messages stored for later retrieval
• How to identify a person/persona? ethereum address or list
  

Ethereum's Role

• Message storage
• Messages stored in the blockchain
• the WHAT of messaging
• Rendezvous Point
• Relationships stored in the blockchain
• the WHO, WHERE, HOW of messaging
• Others (not going to discuss)
  

Message Store

• Benefits
• Ease of broadcast
  
• Anyone with the blockchain can access the message
• No off-chain transport/storage
  
• Asynchronous messages
• Acts as a 'mailbox' that can be retrieved at any time
• Parties don't need to be online to access messages
• Considerations
• Public message boards vs. Private mailboxes
• read protection - encrypted data
• write permission - contract rules limiting access (whitelist of ethereum addresses)
• Other rules (ex: voting, categorizing, 'replying')
  

Message Store - Examples

Naive Eth-mail

• How to use for messaging:
• Creator can suicide mailbox if necessary
• Any other address can send messages in tx.data[0]
• Use app logic to display messages in contract
  

if tx.sender == CONTRACTCREATOR:
     if tx.data[0] == 1:
         suicide(CONTRACTCREATOR)
else:
     NEXTINDEX = contract.storage[999]
     contract.storage[1000 + NEXTINDEX] = tx.data[0]
     contract.storage[999] = NEXTINDEX + 1

Message Store - Examples

Naive Message Board

• How to use for messaging:
• Use tx.data[0] as topic, tx.data[1] as message
• Use app logic to display messages for a topic

// data[0] = topic
// data[1] = message
if tx.data[0]:
    NEXTINDEX = contract.storage[sha3(tx.data[0])]
    contract.storage[sha3(tx.data[0]) + 1 + NEXTINDEX] = tx.data[1]
    contract.storage[sha3(tx.data[0])] = NEXTINDEX + 1 

Rendezvous Point

• Benefits
• Flexible in approach
• use any sort of transport
• Possibly cheaper (less blockchain editing)
  
• Possibility of more real-time communication
• Not limited by 1 minute block updates
• Considerations
• Transport medium (ex: WebRTC, Bitmessage, etc)
• Sync vs. Async (who needs to be online)
  
• storing WHO vs HOW - tradeoffs
  
• WHO - is less likely to change, still worrying about how
• HOW - 'Trusted' communication, but long connection times if multiple handshakes need to be exchanged
  

Interlude - WEBRTC

webrtc.org

• Web Real-time communications
• P2P connections from browser (native, no plugins)
• Secure communication, end-to-end encryption
  
• Audio, video, data connections
• Centralized component in peer discovery
  

Interlude - WebRTC

Connecting to a peer

Rendezvous Point - ExampleS

WHO - Friend list

• Uses ethereum address or contract to signify friend
• How to use for messaging:
• use app logic to only allow connections from 'friends'
  

if tx.sender != CONTRACTCREATOR:
    stop
if tx.data[0] == 0:
    contract.storage[1000+tx.data[1]] = tx.data[2]
elif tx.data[0] == 1:
    suicide(CONTRACTCREATOR)

Rendezvous Point - Examples

WHO - topic-group connection

• Uses ethereum address or contract for connection name/info
• How to use for messaging:
• add address to a topic
• optionally link contract to address
• use address or contract as means to initiate connections
  
• use application logic to only allow connections from your current topic

if tx.data[0] == 0: // update contract
    if tx.data[1] < 1000: // if the contractAddress isn't valid, stop
        stop
    contract.storage[tx.sender] = tx.data[1]
if tx.data[0] == 1: // update topic
    if tx.data[1] < 1000: // if the topic isn't valid, stop
        stop
    if contract.storage[tx.sender + 1]: // if address has an old topic
        TOPICROOT = sha3(32,contract.storage[tx.sender+1]) 
        LEN = contract.storage[TOPICROOT]
        INDEX = contract.storage[tx.sender + 2]
        // set swapped address to new index position and set address index
        contract.storage[TOPICROOT+INDEX] = contract.storage[TOPICROOT+LEN]
        contract.storage[contract.storage[TOPICROOT+INDEX] + 2] = INDEX
        contract.storage[LEN] = 0
        // decrement old topic length
        contract.storage[sha3(32,contract.storage[tx.sender + 1])] = LEN - 1
    TOPICROOT = sha3(32,tx.data[1])
    LEN = contract.storage[TOPICROOT]
    // add address to topic list and increment length
    contract.storage[TOPICROOT+LEN+1] = tx.sender
    contract.storage[TOPICROOT] = LEN + 1
    // store topic and index in list for later lookup
    contract.storage[tx.sender+1] = tx.data[1]
    contract.storage[tx.sender+2] = LEN + 1

End

Questions, comments, corrections?

• caymannava@gmail.com

• caymannava@gmail.com