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Briolett Explainer
An introductory explainer of briolette
Will Drewry
briolette,ecash,cbdc,se,smartcard
pull

Briolette

A framework for digital value exchange

What is it?

  • It's not money
  • It's a way to exchange value -- money, points, credits, whatever!
  • It's a way to exchange value digitally -- with computers, phones, or cards
  • It's a way to directly exchange value digitally -- online or in-person
  • It's a reliable way to directly exchange value digitally -- works anywhere, anytime

What does that mean?

  • You could withdraw money from your bank onto your phone
    • And send it to my phone directly
      • Over email, sms, wifi, bluetooth, NFC, QR code scanning, ...
    • Or pay for a purchase at a store
  • Anything remaining can be deposited back with your bank from your phone or just held

How is it not money then?

  • Money is the combination of payment method and a value guarantee
  • We use digital payments all the time
    • like credit cards or peer-to-peer payment mobile apps
  • Most payments systems today provide their own method of exchange value (called "rails)
    • and guarantee the systems will exchange some underlying fiat value
  • For instance, a merchant may be paid by a credit card or bank transfer
    • The rails connect the payer and payee
    • The value is guaranteed by the businesses involved, like payment providers or banks
  • briolette provides a different approach to rails

What's the approach?

  • Tokens are embued with value by the system operator
    • whether it's a central bank, commercial bank, or private business
    • in most cases, they will assign a monetary value, but it could be frequent flyer points!
  • Similarly, wallets are allowed to send and receive tokens, using cryptography, by the system operator
  • Tokens may then be securely exchanged between users with enabled wallets
  • The digital tokens are used like physical cash
    • Once transferred, the payment is complete and can be immediately spent again

So how is that different?

  • Many of the guarantees and goals are the same
    • Some rails operators even require trusted wallets
  • The difference is largely in how authorization works
  • Most payment rails require an online authorization for a payment to proceed
  • Authorization of a transaction is part of the transaction process not part of the value transfer
    • Delayed authorizations, like when a merchant is offline, work but the merchant cannot access any of that value until they have settled online
  • With briolette, authorization is carried with the value and does not depend on online validation

Can I just cut-and-paste tokens? How could this work?

  • Tokens themselves aren't secret and copying them doesn't help
    • For a token to have value, any transfer must be between valid wallets and signed off by the last wallet to receive it
    • Wallets rely on cryptographic keys and those shouldn't be easily copied or misused
  • Your phone (or other digital wallet) should have a few specific features to help with this
    • by protecting the keys that let you send and receive money from being stolen
    • disallowing transfers of the same token to be signed off more than once (e.g., double spent or "copied")
  • Even if these features get bypassed, briolette still provides a mean to detect and trace when tokens are copied

Wait. Can it trace me?

  • Not at all.
  • Every time a token is transferred from one wallet to another, the sending wallet signs off on it
    • these sign offs are kept as a chain of transfers for each token
  • For legitimate transfers, any wallet's sign off looks like any other
    • except that there may be a random, shared "group" number associated
  • When a token is transferred more than once from the same wallet, its sign offs become connected (or linkable)
    • but the system still doesn't know "who" you are

So how does that help?

  • When a token is shared online with the system operator,
    • branches in the chain of transfers will show if a token has been copied
      • and provide the random group number along with the linkable sign offs
  • This allow wallets avoid other wallets in a known "bad" group
    • and services to disallow wallets from getting new groups if they can be linked to the bad behavior

Why does anyone show the tokens back to the operator?

  • As tokens are transferred, the addition of wallet sign offs cause them to grow
    • At some point, they become too large to exchange and need to be swapped for a fresh token
  • Private banks, or anyone handling large transfers, may wish to validate their tokens, like many do with cash today
    • The operator will provide a validation service for this

Ok, but how do wallets learn about "bad" groups?

  • The system operator posts an update at a regular interval (called 'epochs')
  • Wallets will either collect these updates directly or receive the updates from other wallets when transacting

Why does my wallet need an update?

  • In practice, it doesn't!
  • However, these updates help keep the system reliable
    • If trust in a server or other wallets changes, updates keep your wallet working
  • And wallets cannot perform an infinite number of transactions forever
    • They have to collect 'tickets' which allow them to transact during a time period
    • This time period is defined by the system 'epochs'

This is a lot.

So what happens if my wallet is in a "bad" group?

  • Your wallet will need to go online and get new tickets
    • It may need to "prove" it isn't the misbehaving wallet
  • If the misbehaving wallet was because of a security bug in wallets like yours
    • You may need to update your wallet to get back online
    • Your tokens won't be lost, but it will be an inconvenience

What happens if there aren't any security updates? Am I stuck?

  • It is expected that wallet providers (software and hardware) will meet certain requirements
    • If that doesn't happen, a new wallet may be needed!
  • However, the system operator can still allow you to recover your tokens to the new wallet

Recover? Does that mean I can get my tokens back if I lose my wallet?

  • Yes!
  • If the operator has configured tokens that expire
    • The operator may re-issue tokens back to the last wallet they were seen at
  • In the case of a wallet provider failure, the known broken wallets can indicate the new recipient of the tokens

Expiring tokens seems tricky. Will I lose money?

  • Expiration only means that an online check-in needs to occur before the token can be used again
  • This is a good reason to check in with the operator
    • If the operator knows the (unlinkable) last recipient of a token prior to expiration, it can swap the token
  • If a token is transferred and then let expire without checking in, it's possible that it will be lost
    • Most operators will have a grace period to allow valid transactions to come in after the expiration date
  • The time to recover tokens depends on both the expiration time and grace period

I'd like to learn more.