2025 was my first year working on Bitcoin full time and honestly, it’s been nothing short of incredible. I’m deeply grateful for the people I met along the way, the friendships that grew out of this space, and the inspiring projects I had the privilege to contribute to.

If there’s one thing this year truly taught me, it’s that we’re winning, ladies and gentlemen. Being able to witness this moment firsthand, to build, learn, and grow alongside so many brilliant minds, is something I don’t take for granted.

Feeling excited, humbled, and incredibly stoked to be here for what’s coming next. Happy new years and lots of love to all of you 💜

Important to note thought that this is a major pivot, with all that major pivoting entails.

This is a case of "as it turns out toothbrushes are useful to clean bathtub grout". Which can be true, but still, it's important to stay aware that toothbrushes were designed to brush your teeth with.

nostr wins if it stops trying to be a twitter clone and starts being the invisible layer underneath apps you actually want to use. like bitchat for location-based messaging, diVine for entertainment, whitenoise for private messaging, zap.stream for streaming, shakespeare for vibe coding, etc.

it wins by unbundling into 50 different apps that all talk to each other, rather than one giant app/corp that traps you. it's all about the ecosystem.

The beauty of P2BK is that it provides perfect privacy. Alice and Bob do not need to communicate at all to set it up - all Alice needs is Bob's public key.

The ecash is locked to totally unique blinded public key(s), keeping the receiver's identity private from anyone who views the ecash. This means tokens can be published securely in public.

The sender's identity is also protected, because Alice uses an ephemeral keypair to create the shared secret, and throws it away afterwards. All Bob needs is the ephemeral Public Key!

Now Bob can use the magic of ECDH... he takes his private key (p) and the ephemeral public key that Alice sent with the ecash (E), and he can calculate the SAME shared secret!

He can now use that shared secret to derive a private key to unlock the ecash.

Having calculated the shared secret and blinded the public keys using it, she then send Bob the ecash token, including the ephemeral PUBLIC KEY (E) that she created.

She then calculates a "shared secret" by point-multiplying her ephemeral private key (e) with Bob's public key (P). This gives a shared point (known as "Z").

Here's the magic... this shared point (Z) is the SAME as if she had multiplied her private key (e), Bob's private key (p) and the cryptographic Generator point (G).

But she calculated it using Bob's PUBLIC key.

She then generates a random, temporary keypair (Public Key: E, Private Key: e) known as her "ephemeral key pair".

To start with, Alice obtains Bob's public key (eg from his Nostr profile)...

The magic of ECDH is possible because a person's Public key (eg: NPUB) is their Private key multiplied by the curve base point G.

It's a calculation that simple to do, but pretty much impossible to reverse engineer.

In other words, you can easily calculate a public key (P) given its private key (p), but crucially, you can't calculate a private key from the public key!

Pay to Blinded Key (P2BK) uses Elliptic Curve Diffie-Hellman (ECDH) to establish a shared secret key over a public or insecure channel.

Here's how it works... in layman's terms.

The solution is to "blind" the public keys cryptographically, in a way that only the sender and receiver can reverse.

This makes it easy to link Proofs together, and removes privacy - especially if the Proof is linked to a long-lived public key, such as a Nostr NPUB.

"Pay to Public Key" (P2PK) is the standard way of locking ecash to one or more public keys.

The problem, however, is that these keys are visible in the ecash Proof by design.

Introducing "Pay to Blinded Key" (P2BK) for Cashu - an exciting privacy upgrade for creating P2PK locked proofs.

It's currently a draft specification - likely "NUT-26".

Here's a quick explainer thread 🧵

story time. the recently disclosed nutshell cashu mint vulnerability is as ironic as it gets. it’s very similar to an inscription which is hilarious. as per the cashu spec, a HTLC must have a preimage witness size of 32 bytes.

unfortunately, the mint never checked the size before validating and storing it in its db. we simply overlooked it. since users never paid a fee that depends on the witness size (because we assumed it would be constant), this allowed the attacker to store jpgs of dickbutts in a mints database. for free!

fortunately there’s no messy consensus in cashu. every mint operator dictates their own rules. the fix is simple: now we reject all tokens with a witness that’s too large. those maliciously crafted tokens (of which we haven’t seen any in the wild) can’t be spent anymore.

i must admit, given my recent active engagement in the filter debate, this is probably the funniest exploit possible. i own this one and i’m giggling as i type this. it’s pure comedy.

however, this doesn’t mean the disclosure has gone well. the attacker has proven to be malicious and refused to coordinate with us. instead, he’s putting active mints at risk. this is not how responsible disclosure works. very unprofessional. if you run a mint or know someone who does, update to the latest version (0.18.1) where this issue is fixed. funds were never in danger.

it’s certainly worth a laugh. grill me. this one is simply too good. 😊

thanks to the entire cashu team for their amazing work and their swift reaction. you’ve handled it like pros.

You can also play with locked eCash using Cashu NutLock… nostrly.com/cashu-nutlock/

🥜 #NutNovember

I’ll admit it. I’ve complained about Cashu without ever really using it. Testing and random transactions do not count. So this month, I’m going nuts:

⚡ Using Cashu wallets for zaps and everyday Nostr transactions.

⚡ Treating eCash not as a novelty, but as real Bitcoin on Lightning. Fight me on this!

If we’re serious about freedom tech, we’ve got to use it and not just talk about it.

So for the entire month of November, I’ll be using #Cashu instead of my usual Lightning wallets and I’m inviting you to join me. Let’s see what it’s really like to live on eCash for a month. 🥜💸

Here’s how you can join in:

👉 Option 1: Use cashu.me as your eCash wallet.

It uses npub.cash automatically as your Lightning address.

For zapping, connect your NWC wallets.

Be sure to log in with your browser extension so you use your real npub (otherwise it’ll generate a random one).

👉 Option 2: Try the nostr:npub1kvaln6tm0re4d99q9e4ma788wpvnw0jzkz595cljtfgwhldd75xsj9tkzv app

Use it for both sending zaps with NWC

And your own minibits.cash Lightning address

🪙 Recommended Mints:

mint.chorus.community

mint.minibits.cash/Bitcoin

mint.0xchat.com

I don’t think follow implies obedience at all. People even follow their enemies, it’s about keeping track of information.

Is subscribe a better term than follow?

Could we have a simplified explanation of Cashu for non-coders? I hear a lot about it but it's hard to work out what it is and what it does based the on Nostr posts.

what is cashu??

I love working in open source bitcoin: extremely powerful and subversive technology. purposeful mission with enormous societal impact. top notch talent and intelligent people. intellectually stimulating and challenging. free and open source.

it ticks all the boxes. what a life.

Ooooh! the nostr login on nostrly.com is not working for me

Told my wife that I am a proud vibe coder now. She made this for my notebook 🪿❤️

Do I have to redeem cashu in the mint I got it from? Or can I use any mint?

#asknostr

Hal wrote about Bitcoin banks before Satoshi had invented merged mining. It was the obviously simple scaling solution, but they continued to develop and build.

Bitcoin banks will suffer the same fate as gold-backed banks. The solution is multiple "medium-size" blockchains.

So instead of 10GB blocks on L1, we have ten 1GB sidechains + 1MB L1, secured by Bitcoin miners and cheap enough for businesses to run full archival nodes.

The rest of us can use SPV wallets (and still run a full L1 node), which are massively better than custodians.

LN fit better in the idea. Cashu is more like vouchers.