Hide your nuts!

@gandlaf21

...with Cashu - an eCash system for the Bitcoin Lightning network

@gandlaf21

  • Open source dev
  • Cashu: eCash protocol by @callebtc
  • Nutstash: Cashu wallet

ECash

  • Heard about it?
  • Understand it?
  • Used it?

What is eCash?

  • ECash =/= Bitcoin
  • 1982 by David Chaum
  • Privacy respecting, electronic value transmission protocol
  • Using blind signatures

How does eCash work?

(ELI5)

How does eCash work?

(ELI5)

I want to mint 5$ worth of eCash

Mint Request

How does eCash work?

(ELI5)

I want to mint 5$ worth of eCash

Mint Request

Mint Request Response

Ok, send me 5$ and a secret (inside carbon envelope)

How does eCash work?

(ELI5)

I want to mint 5$ worth of eCash

Mint Request

Mint Request Response

Ok, send me 5$ and a secret (inside carbon envelope)

verysecret..xyz

carbon envelope

How does eCash work?

(ELI5)

I want to mint 5$ worth of eCash

Mint Request

Mint Request Response

Ok, send me 5$ and a secret (inside carbon envelope)

carbon envelope

How does eCash work?

(ELI5)

I want to mint 5$ worth of eCash

Mint Request

Mint Request Response

Ok, send me 5$ and a secret (inside carbon envelope)

carbon envelope

How does eCash work?

(ELI5)

I want to mint 5$ worth of eCash

Mint Request

Mint Request Response

Ok, send me 5$ and a secret (inside carbon envelope)

How does eCash work?

(ELI5)

I want to mint 5$ worth of eCash

Mint Request

Mint Request Response

Ok, send me 5$ and a secret (inside carbon envelope)

Mint

Here is my blinded secret and 5$

How does eCash work?

(ELI5)

I want to mint 5$ worth of eCash

Mint Request

Mint Request Response

Ok, send me 5$ and a secret (inside carbon envelope)

Mint

Here is my blinded secret and 5$

How does eCash work?

(ELI5)

I want to mint 5$ worth of eCash

Mint Request

Mint Request Response

Ok, send me 5$ and a secret (inside carbon envelope)

Mint

Here is my blinded secret and 5$

How does eCash work?

(ELI5)

I want to mint 5$ worth of eCash

Mint Request

Mint Request Response

Ok, send me 5$ and a secret (inside carbon envelope)

Mint

Here is my blinded secret and 5$

How does eCash work?

(ELI5)

I want to mint 5$ worth of eCash

Mint Request

Mint Request Response

Ok, send me 5$ and a secret (inside carbon envelope)

Mint

Here is my blinded secret and 5$

Mint Response

I return your blinded secret with mints signature

How does eCash work?

(ELI5)

I want to mint 5$ worth of eCash

Mint Request

Mint Request Response

Ok, send me 5$ and a secret (inside carbon envelope)

Mint

Here is my blinded secret and 5$

Mint Response

I return your blinded secret with mints signature

How does eCash work?

(ELI5)

I want to mint 5$ worth of eCash

Mint Request

Mint Request Response

Ok, send me 5$ and a secret (inside carbon envelope)

Mint

Here is my blinded secret and 5$

Mint Response

I return your blinded secret with mints signature

How does eCash work?

(ELI5)

I want to mint 5$ worth of eCash

Mint Request

Mint Request Response

Ok, send me 5$ and a secret (inside carbon envelope)

Mint

Here is my blinded secret and 5$

Mint Response

I return your blinded secret with mints signature

How does eCash work?

(ELI5)

I want to mint 5$ worth of eCash

Mint Request

Mint Request Response

Ok, send me 5$ and a secret (inside carbon envelope)

Mint

Here is my blinded secret and 5$

Mint Response

I return your blinded secret with mints signature

  • The mint has never seen our secret                

How does eCash work?

(ELI5)

I want to mint 5$ worth of eCash

Mint Request

Mint Request Response

Ok, send me 5$ and a secret (inside carbon envelope)

Mint

Here is my blinded secret and 5$

Mint Response

I return your blinded secret with mints signature

  • The mint has never seen our secret
  • The mint can verify the secret validity/amount because of the stamp

How does eCash work?

(ELI5)

I want to mint 5$ worth of eCash

Mint Request

Mint Request Response

Ok, send me 5$ and a secret (inside carbon envelope)

Mint

Here is my blinded secret and 5$

Mint Response

I return your blinded secret with mints signature

  • The mint has never seen our secret
  • The mint can verify the secret validity/amount because of the stamp
  • Bearer token

How does Cashu work?

Mint Request

Mint Request Response

Mint

Mint Response

How does Cashu work?

I want to mint 8 sats worth of eCash

Mint Request

Mint Request Response

Mint

Mint Response

How does Cashu work?

I want to mint 8 sats worth of eCash

Mint Request

Mint Request Response

Mint

Mint Response

Ok, pay LN-invoice and send blinded secret

await payment...

How does Cashu work?

I want to mint 8 sats worth of eCash

Mint Request

Mint Request Response

Mint

Mint Response

Ok, pay LN-invoice and send blinded secret

await payment...

How does Cashu work?

I want to mint 8 sats worth of eCash

Mint Request

Mint Request Response

Mint

Mint Response

Ok, pay LN-invoice and send blinded secret

await payment...

How does Cashu work?

I want to mint 8 sats worth of eCash

Mint Request

Mint Request Response

Mint

Mint Response

Ok, pay LN-invoice and send blinded secret

await payment...

How does Cashu work?

I want to mint 8 sats worth of eCash

Mint Request

Mint Request Response

Mint

Mint Response

Ok, pay LN-invoice and send blinded secret

await payment...

B_

Y

+

r

G

=

Y: secret

r: blinding factor

How does Cashu work?

I want to mint 8 sats worth of eCash

Mint Request

Mint Request Response

Mint

Mint Response

Ok, pay LN-invoice and send blinded secret

await payment...

B_

Y

r

How does Cashu work?

I want to mint 8 sats worth of eCash

Mint Request

Mint Request Response

Mint

Mint Response

Ok, pay LN-invoice and send blinded secret

await payment...

B_

Y

r

Here is my blinded secret and payment hash

How does Cashu work?

I want to mint 8 sats worth of eCash

Mint Request

Mint Request Response

Mint

Mint Response

Ok, pay LN-invoice and send blinded secret

await payment...

B_

Y

r

Here is my blinded secret and payment hash

How does Cashu work?

I want to mint 8 sats worth of eCash

Mint Request

Mint Request Response

Mint

Mint Response

Ok, pay LN-invoice and send blinded secret

await payment...

B_

Y

r

Here is my blinded secret and payment hash

PUB PRIV Amount
123abc afd890 1
... ... ...
456def 876acb 8

K

k

How does Cashu work?

I want to mint 8 sats worth of eCash

Mint Request

Mint Request Response

Mint

Mint Response

Ok, pay LN-invoice and send blinded secret

await payment...

Y

r

Here is my blinded secret and payment hash

PUB PRIV Amount
123abc afd890 1
... ... ...
456def 876acb 8

K

k

*

=

C_

B_

8

How does Cashu work?

I want to mint 8 sats worth of eCash

Mint Request

Mint Request Response

Mint

Mint Response

Ok, pay LN-invoice and send blinded secret

await payment...

Y

r

Here is my blinded secret and payment hash

PUB PRIV Amount
123abc afd890 1
... ... ...
456def 876acb 8

K

k

C_

How does Cashu work?

I want to mint 8 sats worth of eCash

Mint Request

Mint Request Response

Mint

Mint Response

Ok, pay LN-invoice and send blinded secret

await payment...

Y

r

Here is my blinded secret and payment hash

PUB PRIV Amount
123abc afd890 1
... ... ...
456def 876acb 8

K

k

C_

I return your blinded secret with mints signature

How does Cashu work?

I want to mint 8 sats worth of eCash

Mint Request

Mint Request Response

Mint

Mint Response

Ok, pay LN-invoice and send blinded secret

await payment...

Y

r

Here is my blinded secret and payment hash

PUB PRIV Amount
123abc afd890 1
... ... ...
456def 876acb 8

K

k

I return your blinded secret with mints signature

-

*

=

C

C_

8

How does Cashu work?

I want to mint 8 sats worth of eCash

Mint Request

Mint Request Response

Mint

Mint Response

Ok, pay LN-invoice and send blinded secret

await payment...

Y

Here is my blinded secret and payment hash

PUB PRIV Amount
123abc afd890 1
... ... ...
456def 876acb 8

k

I return your blinded secret with mints signature

C

How does Cashu work?

I want to mint 8 sats worth of eCash

Mint Request

Mint Request Response

Mint

Mint Response

Ok, pay LN-invoice and send blinded secret

await payment...

Y

Here is my blinded secret and payment hash

PUB PRIV Amount
123abc afd890 1
... ... ...
456def 876acb 8

k

I return your blinded secret with mints signature

C

*

==

How does Cashu work?

How does Cashu work?

How does Cashu work?

  • Wallets use the mints LN node
  • No balance, no ID, no UTXOs

How does Cashu work?

  • Wallets use the mints LN node
  • No balance, no ID, no UTXOs
  • Mints inerop over LN
  • Private ecash transactions

Why Cashu?

  • LN self custody is "hard"
  • LN privacy is complicated
  • User data ownership
  • Bearer tokens UX

Cashu usage

Mints

Wallets

cashu nutshell

cashu nutshell

feni

feni

redeem

Nutstash usage

Nutstash usage

https://wallet.nutstash.app

Nutstash usage

https://wallet.nutstash.app

Connect with mints

Nutstash usage

https://wallet.nutstash.app

Connect with mints

Use Wallet

Nutstash usage

Send

Receive

Mint

Pay LN invoice

Nutstash usage

Swap between mints

Integrate with nostr

Nutstash usage

demo

Other usages?

We've seen...

  • Private LN payments using custodians
  • Sending bearer asset tokens via DMs

Other usages?

We've seen...

  • Private LN payments using custodians
  • Sending bearer asset tokens via DMs

Yet to come....

  • Paid REST requests (X-Cashu)
  • Cashu nostr relays
  • ...

Cashu development

We're not there yet...

Join us!

  • Token backups
  • Fractional reserve rug-pulling
  • Making it easy for developers and user: Simple protocol, great libraries & easy to run software

Cashu development

Join us!

@gandlaf21

https://gandlaf.com