BRC-85

Proven Identity Key Exchange (PIKE)

Two people who want to transact need each other's public key, and sending it over a channel someone could tamper with is a real risk. This uses a short code shared out of band to confirm the key really came from the right person.

Darren Kellenschwiler, Damian Orzepowski7 Jun 20245 min read

Why: A hosted paymail server could be compromised and hand out a fake public key for a contact without either party noticing.
What: BRC-85 (Proven Identity Key Exchange, PIKE) is a paymail-based flow for two wallets to exchange public keys and then confirm, using a shared secret and a one time code shared off channel, that the exchange was not tampered with.
How: Two wallets swap contact requests and generated public keys through their paymail servers, then each side derives a shared secret from its own private key and the counterparty's public key, generates a Time-based One Time Password (TOTP) from that secret, and the humans read the codes to each other out of band to…

What this lets you do

Send a contact request to another paymail address
Accept or reject an incoming contact request
Derive a shared secret from a private key and a peer's public key
Generate and compare a TOTP to confirm a key exchange was not tampered with
Detect a compromised or malicious paymail server before trusting a key

Written by claude-sonnet-5 from the specification text. Where the two differ, the original is correct.

Reference for an AI

Everything an assistant needs to answer questions about BRC-85 accurately, including what it depends on.

The specification

Read the original

Abstract

Allowing humans to securely exchange public keys using web apis and an off channel sharing of TOTPs.

Motivation

When you use hosted servers for payment output generation there's no way to detect if the host has been compromised and is sharing keys not associated with the intended recipient.

BRFCID

A random ID was generated in order to avoid label collisions in the capability document of a paymail server.

brfcid: 8c4ed5ef8ace
title: Proven Identity Key Exchange (PIKE)
author: Darren Kellenschwiler, Damian Orzepowski
version: 1.0.0

Specification

Roughly speaking you create a shared secret between you and the counterparty using their public key and your private key. If you each do this you can arrive at a shared secret. You then derive a time hashed one time pass code to prove you both have the same value - each sharing the TOTP and validating the counterparty's. Thereafter you can use that public key knowing that it really is that counterparty without fear of MITM attacks.

Implementations

SPV Wallet

Flow

Sender wallet: generate random hash
Sender wallet generate public key from private key and random hash
Sender wallet is sending "add contact request" to Sender BUX containing: a. contact paymail address b. random hash c. generated public key
Sender BUX is performing Paymail host discovery (which is described on this page: https://tsc.bsvblockchain.org/standards/paymail/#ServiceDiscovery)
Sender BUX is performing Paymail capability discovery on Receiver BUX by requesting /.well-known/bsvalias
If Receiver BUX doesn't contain Proven Identity Key Exchange (PIKE) capability, Sender BUX should return an error to Sender Wallet
else the Sender BUX is sending a "Add a contact" request to Receiver BUX on the endpoint provided in PIKE capability. This request contains: a. sender paymail address b. random hash c. generated public key
Receiver BUX stores that "contact" as "waiting" in database
Receiver BUX is answering to Sender BUX with success
Sender BUX is storing the "contact" as "waiting"
Receiver Wallet asks Receiver BUX for "waiting" "contact" to confirm or reject
Receiver BUX is responding with the list of contacts
If Receiver Wallet reject the contact, then: a. it is sending rejection request to Receiver BUX b. Receiver BUX is removing the contact from database c. In that case the flow ends
else: Receiver Wallet generate public key from private key and random hash from the contact
Receiver Wallet is sending the request for Receiver BUX for accepting the contact with informations: a. paymail address for contact to accept b. generated public key
Receiver BUX is marking a "contact" as "accepted"
Receiver BUX is sending the "contact accepted" request to Sender BUX with: a. paymail address of Receiver b. generated public key c. random hash
Sender BUX is validating random hash, and stores received public key in "contact" and marks it as accepted
Sender Wallet is asking Sender to confirm contact
Sender asks Receiver for TOTP
Receiver checks TOTP for Senders paymail in Receiver Wallet
Receiver Wallet calculates shared secret based on private key and Senders public key
Receiver Wallet generates TOTP based on shared secret
Receiver Wallet sends back TOTP to Receiver
Receiver is responding with TOTP to Sender
Sender is providing TOTP to Sender Wallet
Sender Wallet calculates shared secret based on private key and Receiver public key
Sender Wallet generates TOTP based on shared secret
Sender Wallet is comparing received TOTP with generated TOTP. If their match then it marks contact as confirmed.
Sender Wallet is now generating another TOTP and provides to Sender
Sender is providing TOTP to Receiver
Receiver is providing TOTP to Receiver Wallet
Receiver Wallet is generating TOTP and comparing it with received TOTP If their match then it marks contact as confirmed.

sequenceDiagram
actor Sender
participant Sender Wallet
participant Sender BUX
participant Receiver BUX
participant Receiver Wallet
actor Receiver

    Sender->>Sender Wallet: Add receiver as contact
    activate Sender Wallet
    Sender Wallet->>Sender Wallet: Generate random hash
    Sender Wallet->>Sender Wallet: Generate public key from private key and random hash
    deactivate Sender Wallet
    activate Sender Wallet
    Sender Wallet->>Sender BUX: Add contact request
    activate Sender BUX
    Sender BUX->>Sender BUX: Paymail host discovery
    Sender BUX->>Receiver BUX: Paymail capability discovery
    activate Receiver BUX
    Sender BUX->>Receiver BUX: Add a contact request
    Receiver BUX->>Receiver BUX: Store contact as "waiting" in database
    Receiver BUX->>Sender BUX: Success
    deactivate Receiver BUX
    Sender BUX->>Sender BUX: Store contact as "waiting"
    Sender BUX->>Sender Wallet: success
    deactivate Sender BUX
    Sender Wallet->>Sender: Display success
    deactivate Sender Wallet
    
    Receiver Wallet->>Receiver BUX: Get "waiting" "contact" to confirm or reject
    activate Receiver Wallet
    activate Receiver BUX
    Receiver BUX->>Receiver Wallet: List of contacts
    deactivate Receiver BUX
    alt reject contatct
        Receiver Wallet->>Receiver BUX: Rejection request
        activate Receiver BUX
        Receiver BUX->>Receiver BUX: Remove contact from database
        deactivate Receiver BUX
    else accept contact
        Receiver Wallet->>Receiver Wallet: Generate public key from private key and random hash
        Receiver Wallet->>Receiver BUX: Accept contact request
        activate Receiver BUX
        Receiver BUX->>Receiver BUX: Mark contact as "accepted"
        Receiver BUX->>Sender BUX: Contact accepted request
        Sender BUX->>Sender BUX: Validate random hash and store received public key
        Sender BUX->>Receiver BUX: success
        Receiver BUX->>Receiver Wallet: success
        deactivate Receiver BUX
        deactivate Receiver Wallet
    end
    Sender Wallet->>Sender: Confirm contact?
    activate Sender
    Sender->>Receiver: TOTP request
    activate Receiver
    activate Receiver
    Receiver->>Receiver Wallet: Check TOTP for Senders paymail
    activate Receiver Wallet
    Receiver Wallet->>Receiver Wallet: Calculate shared secret based on private key and Senders public key
    Receiver Wallet->>Receiver Wallet: Generate TOTP based on shared secret
    Receiver Wallet->>Receiver: TOTP
    deactivate Receiver Wallet
    Receiver->>Sender: TOTP
    deactivate Receiver
    Sender->>Sender Wallet: TOTP
    activate Sender
    activate Sender Wallet
    Sender Wallet->>Sender Wallet: Calculate shared secret based on private key and Receiver public key
    Sender Wallet->>Sender Wallet: Generate TOTP based on shared secret
    Sender Wallet->>Sender Wallet: Compare received TOTP with generated TOTP
    Sender Wallet->>Sender Wallet: Mark contact as confirmed
    Sender Wallet->>Sender Wallet: Generate another TOTP
    Sender Wallet->>Sender: TOTP
    deactivate Sender Wallet
    deactivate Sender
    Sender->>Receiver: TOTP
    deactivate Sender
    activate Receiver
    Receiver->>Receiver Wallet: TOTP
    activate Receiver Wallet
    Receiver Wallet->>Receiver Wallet: Generate TOTP and compare it with received TOTP
    Receiver Wallet->>Receiver Wallet: Mark contact as confirmed
    deactivate Receiver Wallet
    deactivate Receiver
    deactivate Receiver

Was this helpful?

Summary