Why Nostr Needs a C Library: Lessons from the Trenches

Built by embedded developers who were tired of being told to "just use Node.js."

Years ago I was exploring how to add Nostr support to embedded systems and resource-constrained devices. Every Nostr library I found required Node.js, Python, or Rust with massive runtime overhead.

That's when it hit me: we're building the wrong tools for the wrong problems.

The Embedded Developer's Dilemma

Here's a reality check: the most important devices in the Bitcoin ecosystem don't run JavaScript. They run C.

• Bitcoin Core: C++

• Lightning Network Daemon: Go (but talks to C libraries)

• Hardware wallets: C on microcontrollers

• Bitcoin ASICs: C firmware

• Lightning nodes on Raspberry Pi: Resource-constrained C

Yet when these systems need to speak Nostr, we tell them to spin up a Node.js instance. It's like requiring a semi-truck to deliver a letter.

libnostr-c: Built Different

I spent a while building what should have existed from day one: a pure C implementation of Nostr. No runtime. No garbage collector. No package manager. Just clean, portable C99 that compiles anywhere.

The results speak for themselves:

Performance Benchmarks:

• Key generation: 2,500 µs (JavaScript) → 47 µs (libnostr-c) = 53x faster

• Event signing: 850 µs (JavaScript) → 49 µs (libnostr-c) = 17x faster

• Binary size: 85 MB (JavaScript) → 100 KB (libnostr-c) = 850x smaller

• Startup time: 800 ms (JavaScript) → <1 ms (libnostr-c) = 800x faster

But performance wasn't the goal. Integration was.

The Integration Story

Hardware Wallet Integration (Conceptual)

// This COULD run on a device with 256KB RAM
void wallet_post_transaction_note(const char* txid, uint64_t amount) {
    nostr_event* event = nostr_event_create();
    
    char content[256];
    snprintf(content, sizeof(content), 
             "Sent %llu sats. TX: %s", amount, txid);
    
    nostr_event_set_content(event, content);
    nostr_event_add_tag(event, "t", "bitcoin-tx");
    nostr_event_sign(event, &device_privkey);
    
    // Queue for broadcast when connected
    queue_nostr_event(event);
}

The library is designed to make this possible, the code is small enough and efficient enough for embedded use.

Bitcoin Node Integration

// Inside Bitcoin Core/Knots (conceptual)
void broadcast_block_found(const CBlock& block) {
    if (!nostr_enabled) return;
    
    nostr_event* event = nostr_event_create();
    nostr_event_set_kind(event, 1);
    
    char msg[512];
    sprintf(msg, "New block at height %d: %s", 
            block.height, block.GetHash().ToString().c_str());
    
    nostr_event_set_content(event, msg);
    nostr_event_sign(event, &node_privkey);
    
    relay_to_nostr(event);
}

Lightning Node Status Updates

// LND plugin using libnostr-c
void publish_channel_update(const channel_t* chan) {
    nostr_event* event = nostr_event_create();
    nostr_event_set_kind(event, 38000); // Lightning channel update
    
    // Add channel metadata as tags
    nostr_event_add_tag(event, "channel_id", chan->id);
    nostr_event_add_tag(event, "capacity", 
                        itoa(chan->capacity_sats));
    nostr_event_add_tag(event, "status", 
                        chan->active ? "active" : "inactive");
    
    nostr_event_sign(event, &node_privkey);
    broadcast_to_relays(event);
}

The Cryptography Challenge

Modern Nostr requires NIP-44 encryption. Most libraries punt this to OpenSSL or libsodium, adding megabytes of dependencies. We integrated noscrypt directly, getting:

• Constant-time operations (no timing attacks)

• Minimal code size (25KB for full NIP-44)

• Zero allocations in the crypto path

• Hardware acceleration where available

// End-to-end encrypted DMs on embedded devices
void send_encrypted_dm(const char* recipient_pubkey_hex, 
                      const char* message) {
    nostr_key recipient;
    nostr_key_from_hex(recipient_pubkey_hex, &recipient);
    
    uint8_t ciphertext[1024];
    size_t ciphertext_len;
    
    // One function call, no async complexity
    nostr_nip44_encrypt(&my_privkey, &recipient,
                        (uint8_t*)message, strlen(message),
                        ciphertext, &ciphertext_len);
    
    // Create kind 44 event with encrypted content
    nostr_event* dm = create_encrypted_dm_event(
        recipient_pubkey_hex, ciphertext, ciphertext_len
    );
    
    relay_event(dm);
}

Lightning Wallet Connect: The Killer Feature

NIP-47 (Nostr Wallet Connect) is how Lightning wallets communicate. Every implementation I found required WebSockets, JSON-RPC libraries, and async event loops. On embedded systems? Forget it.

libnostr-c makes it trivial:

// Complete Lightning payment flow in C
void pay_invoice_via_nwc(const char* invoice) {
    // Parse connection from QR/string
    struct nwc_connection* wallet;
    nostr_nip47_parse_connection_uri(saved_nwc_uri, &wallet);
    
    // Create payment request
    struct nwc_request req = {
        .method = "pay_invoice",
        .params.invoice = invoice
    };
    
    // Send and wait for response
    struct nwc_response* resp;
    nostr_nip47_send_request(wallet, &req, &resp);
    
    if (resp->error) {
        printf("Payment failed: %s\n", resp->error->message);
    } else {
        printf("Payment sent! Preimage: %s\n", 
               resp->result.preimage);
    }
}

This same code works on a Linux server, a Raspberry Pi, or an STM32 microcontroller.

Potential Use Cases

What You Could Build

1. Hardware Wallet Integration

   • Sign Nostr events with same keys as Bitcoin transactions

   • Post transaction notes to user's relays

   • Total code addition: <5KB

2. Lightning ATM

   • ESP32-based Bitcoin ATM

   • Post transaction receipts to Nostr

   • Enable social proof of liquidity

3. Mining Pool Monitor

   • Publish block finds in real-time

   • Share difficulty adjustments

   • Miner performance stats

4. Mesh Network Nodes

   • Raspberry Pi mesh networks

   • Nostr as transport protocol

   • Works without internet backhaul

The Performance Deep Dive

Let's talk about why C matters for Nostr:

Memory Allocation Patterns

JavaScript:

// Every operation allocates
const event = new NostrEvent();  // Heap allocation
event.tags.push(['p', pubkey]); // Array resize, more allocation
const json = JSON.stringify(event); // String allocation

libnostr-c:

// Stack allocation, predictable memory
nostr_event event_storage;
nostr_event* event = nostr_event_init(&event_storage);

// Tags use arena allocator - one malloc for all tags
nostr_event_add_tag(event, "p", pubkey); // No individual mallocs

Benchmark Methodology

Our performance numbers come from real measurements:

// How we measure
for (int i = 0; i < 10000; i++) {
    uint64_t start = get_nsec_time();
    
    nostr_key_generate(&privkey, &pubkey);
    
    uint64_t elapsed = get_nsec_time() - start;
    total_time += elapsed;
}
average = total_time / 10000; // 47,234 nanoseconds

What's Next?

libnostr-c is just the beginning. The roadmap:

Medium Term

• Additional NIP Support

• Hardware security module support

• SIMD optimizations for batch operations

• WebAssembly compilation target

• Relay pooling and management

• Embedded-friendly SQLite integration

• Bluetooth transport for offline signing

Long Term

• Formal verification of crypto code

• Integration into Bitcoin Core/Knots as optional module

• Standard C library for all Nostr implementations

Try It Today

The code is real, tested, and ready:

# Clone and build
git clone https://github.com/privkeyio/libnostr-c.git
cd libnostr-c
mkdir build && cd build
cmake ..
make

# Run the test suite
make test

# Benchmark on your hardware
./benchmark/bench_runner

The Bottom Line

We built the infrastructure layer that Nostr was missing. Not because C is trendy (it's not), but because the devices that matter run C.

Every Lightning node that can't post status updates, every hardware wallet that can't sign events, every embedded system locked out of Nostr, they're all waiting for tools built for their constraints.

libnostr-c is that tool. Battle-tested on real hardware, optimized for real constraints, ready for real deployment.

Get Started: GitHub Repository

Contact:

• Nostr:

  • npub1acr7ycax3t7ne8xzt0kfhh33cfd5z4h8z3ntk00erpd7zxlqzy3qrn2tqw

  • npub1h3fzzzeq60acjvnyvw34rpn5clkaueteffmkt3ln4ygekg9lcm0qhw96sj

• Email:

  • kyle@privkey.io

  • william@privkey.io

• GitHub: @privkeyio