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EuroToken: Protocol specifics

Previously, the app had zero indication of whether the counterparty was to be trusted. Our pull request attempts to create a 'web of trust' by transceiving public keys that counterparties transacted with in the past.

An unknown public key currently receives a trust score of 0. Upon receiving a message containing a known public key, the trust score is incremented by 1 (up to 100). The following sequence diagram describes the trust update protocol. To transceive the list of 50 public keys, the EVA protocol is utilized.

Sequence diagram showing public key transmission

EVA protocol specifics

Sending public keys

  • As mentioned, we use the EVA protocol to transmit a binary blob of encoded public keys to the other party.
  • TransactionsPayload serializes and deserializes n public keys seperated by comma's into a correct payload.
  • serializePacket is called to construct an encrypted pcket containing the payload and message identifier (MessageId.ATTACHMENT) such that only the counterparty can decrypt the message with it's private key.
  • evaSendBinary(peer, 'eva_last_addresses', payload.id, packet) is called to finally transmit the binary.

Receiving public keys

  • Upon receiving a packet, the messageHandlers list is checked for matching handler calls in nl.tudelft.trustchain.eurotoken/community/EuroTokenCommunity.kt.
  • MessageId.ATTACHMENT is matched to the last addresses packet and onLastAddressPacket is called.
  • The packet is decrypted using packet.getDecryptedAuthPayload.
  • myTrustStore.incrementTrust(address) is called for every address found in the payload. Trust Score popup Demo

Changelog

  • Added TrustStore.db to store and update public key + trust score pairs.
  • Added demo mode to EuroToken, which can be toggled on in the topright options corner. Demo mode is used to generate random keys for transmitting, in case when a fresh app has no transactions.
  • Added transceiving of public keys. On receive; update trust score by 1 (default is 0). Send latest 50 transaction public keys after sending EuroTokens to someone.
  • Added a visualization of the trust score of the counterparty you are transacting with. Check out TrustScoresFragment.kt
  • Improved string localization; move strings to eurotoken/src/main/res/values/strings.xml