generate nostr keys using NIP-06 derivation key

README.md

@@ -9,8 +9,8 @@ instead of a mnemonic seed phrase.
 
 ```
 $ brainseed seed
-Entropy prompt: hello world
-Confirm: hello world
+> Entropy prompt: hello world
+> Confirm: hello world
 cliff burden nut payment negative soccer one mad pulse balcony force inside
 ```
 
@@ -22,8 +22,8 @@ Directly generate a watch-only output descriptor, to import into a wallet like S
 
 ```
 $ brainseed watch
-Entropy prompt: hello world
-Confirm: hello world
+> Entropy prompt: hello world
+> Confirm: hello world
 wpkh([b343958c/84'/1'/0']tpubDCCj6osNwAnnSqViJQjqHD9xkJ6UXKT73ZB36W5gNapyCmirdibyzHeRsAYK5z9V5fi4ZdGAGA2jbXxPD1qS3Yht2tU3shPuatfUUWvKeCc/0/*)#cj35ttn3
 ```
 ## Signing a transaction
@@ -32,12 +32,26 @@ This can be used to sign files as well, if you don't want to use a seed phrase i
 
 ```
 $ brainseed sign input.psbt output.psbt
-Entropy prompt: hello world
-Confirm: hello world
+> Entropy prompt: hello world
+> Confirm: hello world
 ```
 
 After importing a watch-only wallet into something like Sparrow, generate a transaction and save it as a raw file. Then sign it with this command, and load it back into Sparrow.
 
+## Nostr keys
+
+Nostr's NIP-06 specifies the derivation path for generaing key pair's from Bitcoin seeds. By default, the derivation path is `m/44'/1237'/0'/0/0`. You can now generate key pairs like this:
+
+```
+$ brainseed nostr
+> Entropy prompt: hello world
+> Confirm: hello world
+Private: 69cae0b7638b0eee28044b555dbe9063a3ded632bbfc3d3e3f2778467617d1e6
+Public:  b3a19b7ef2749552db88fd43300db72484c4520a0ee84ae5881df871f1d84369
+```
+
+You can pass `--nip19` to use the bech32 encoding from NIP-19 (better known as the `npub/nsec` encoding). Additionally, you can specify additional indexes on the derivation path by using `-i <NUMBER>`. For instance, `-i 1` will use the derivation path `m/44'/1237'/0'/0/1`. This might be useful if you wish to rotate keys.
+
 ## Frequently Asked Questions
 
 ### This is horrible. Why would you do such a thing?

src/cli.rs

@@ -3,8 +3,12 @@ use std::{io::Write, path::PathBuf};
 use anyhow::Context;
 use bdk::{
     bitcoin::{
+        bech32::{encode, ToBase32, Variant},
         consensus::{deserialize, serialize},
+        hashes::hex::ToHex,
         psbt::PartiallySignedTransaction,
+        secp256k1::Secp256k1,
+        util::bip32::{DerivationPath, ExtendedPrivKey},
         Network,
     },
     database::MemoryDatabase,
@@ -42,6 +46,7 @@ impl Cli {
             Action::Seed => self.write_output(seed.to_string().as_bytes()),
             Action::Sign { input, output } => self.sign(input, output, seed),
             Action::Watch => self.show_descriptor(seed),
+            Action::Nostr { nip19, index } => self.nostr(seed, *nip19, *index),
         }
     }
 
@@ -122,6 +127,31 @@ impl Cli {
             Network::Bitcoin
         }
     }
+
+    fn nostr(&self, seed: Mnemonic, nip19: bool, index: u32) -> Result<(), anyhow::Error> {
+        let ctx = Secp256k1::new();
+        let dv: DerivationPath = format!("m/44'/1237'/0'/0/{index}")
+            .parse()
+            .context("Invalid derivation path for nostr")?;
+        let seed = seed.to_seed("");
+        let master = ExtendedPrivKey::new_master(Network::Bitcoin, &seed)?;
+        let xpriv = master.derive_priv(&ctx, &dv)?;
+        let privkey = xpriv.to_priv();
+        let pubkey = privkey.public_key(&ctx);
+
+        let (pubkey, privkey) = match nip19 {
+            true => (
+                encode("nsec", privkey.to_bytes().to_base32(), Variant::Bech32)?,
+                encode("npub", pubkey.to_bytes().to_base32(), Variant::Bech32)?,
+            ),
+            false => (pubkey.to_bytes()[1..].to_hex(), privkey.to_bytes().to_hex()),
+        };
+
+        println!("Private: {privkey}");
+        println!("Public:  {pubkey}");
+
+        Ok(())
+    }
 }
 
 #[derive(clap::Subcommand, Clone)]
@@ -134,4 +164,16 @@ pub enum Action {
 
     /// Show wallet descriptor that is useful for importing as a watch-only wallet.
     Watch,
+
+    /// Generate a Nostr private/public keypair (optionally in NIP-19 encoding).
+    Nostr {
+        /// Serialize the keys according to NIP-19 (npub/nsec format).
+        #[clap(long)]
+        nip19: bool,
+
+        /// Child index for the derivation path m/44'/1237'/0'/0.
+        /// Use this to create additional keys for your seed.
+        #[clap(short, long, default_value_t = 0)]
+        index: u32,
+    },
 }