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NOSTR Core Library - Usage Guide

Overview

The NOSTR Core Library (libnostr_core) is a self-contained, exportable C library for NOSTR protocol implementation. It requires no external cryptographic dependencies (no OpenSSL, no libwally) and can be easily integrated into other projects.

Key Features

Self-Contained Crypto: All cryptographic operations implemented from scratch
Zero External Dependencies: Only requires standard C library, cJSON, and libwebsockets
Cross-Platform: Builds on Linux, macOS, Windows (with appropriate toolchain)
NIP-06 Compliant: Proper BIP39/BIP32 implementation for key derivation
Thread-Safe: Core cryptographic functions are stateless and thread-safe
Easy Integration: Simple C API with clear error handling

File Structure for Export

Core Library Files (Required)

libnostr_core/
├── nostr_core.h           # Main public API header
├── nostr_core.c           # Core implementation
├── nostr_crypto.h         # Crypto implementation header
├── nostr_crypto.c         # Self-contained crypto implementation
├── Makefile              # Build configuration
└── cjson/                # JSON library (can be replaced with system cJSON)
    ├── cJSON.h
    └── cJSON.c

Optional Files

├── examples/             # Usage examples (helpful for integration)
├── LIBRARY_USAGE.md     # This usage guide
├── SELF_CONTAINED_CRYPTO.md  # Crypto implementation details
└── CROSS_PLATFORM_GUIDE.md  # Platform-specific build notes

Integration Methods

Method 1: Static Library Integration

Copy Required Files:

cp nostr_core.h nostr_core.c nostr_crypto.h nostr_crypto.c /path/to/your/project/
cp -r cjson/ /path/to/your/project/

Build Static Library:

gcc -c -fPIC nostr_core.c nostr_crypto.c cjson/cJSON.c
ar rcs libnostr_core.a nostr_core.o nostr_crypto.o cJSON.o

Link in Your Project:

gcc your_project.c -L. -lnostr_core -lm -o your_project

Method 2: Direct Source Integration

Simply include the source files directly in your project:

// In your project
#include "nostr_core.h"

// Compile with:
// gcc your_project.c nostr_core.c nostr_crypto.c cjson/cJSON.c -lm

Method 3: Shared Library Integration

Build Shared Library:
```
make libnostr_core.so
```

Install System-Wide (optional):

sudo cp libnostr_core.so /usr/local/lib/
sudo cp nostr_core.h /usr/local/include/
sudo ldconfig

Use in Projects:
```
gcc your_project.c -lnostr_core -lm
```

Basic Usage Example

#include "nostr_core.h"
#include <stdio.h>
#include <stdlib.h>

int main() {
    // Initialize the library
    if (nostr_init() != NOSTR_SUCCESS) {
        fprintf(stderr, "Failed to initialize NOSTR library\n");
        return 1;
    }
    
    // Generate a keypair
    unsigned char private_key[32];
    unsigned char public_key[32];
    
    if (nostr_generate_keypair(private_key, public_key) != NOSTR_SUCCESS) {
        fprintf(stderr, "Failed to generate keypair\n");
        nostr_cleanup();
        return 1;
    }
    
    // Convert to hex and bech32
    char private_hex[65], public_hex[65];
    char nsec[100], npub[100];
    
    nostr_bytes_to_hex(private_key, 32, private_hex);
    nostr_bytes_to_hex(public_key, 32, public_hex);
    nostr_key_to_bech32(private_key, "nsec", nsec);
    nostr_key_to_bech32(public_key, "npub", npub);
    
    printf("Private Key: %s\n", private_hex);
    printf("Public Key:  %s\n", public_hex);
    printf("nsec:        %s\n", nsec);
    printf("npub:        %s\n", npub);
    
    // Create and sign an event
    cJSON* event = nostr_create_text_event("Hello NOSTR!", private_key);
    if (event) {
        char* event_json = cJSON_Print(event);
        printf("Signed Event: %s\n", event_json);
        free(event_json);
        cJSON_Delete(event);
    }
    
    // Cleanup
    nostr_cleanup();
    return 0;
}

Dependency Management

Required Dependencies

Standard C Library: malloc, string functions, file I/O
Math Library: -lm (for cryptographic calculations)
cJSON: JSON parsing (included, or use system version)

Optional Dependencies

libwebsockets: Only needed for relay communication functions
System cJSON: Can replace bundled version

Minimal Integration (Crypto Only)

If you only need key generation and signing:

# Build with minimal dependencies
gcc -DNOSTR_CRYPTO_ONLY your_project.c nostr_crypto.c -lm

Cross-Platform Considerations

Linux

Works out of the box with GCC
Install build-essential: sudo apt install build-essential

macOS

Works with Xcode command line tools
May need: xcode-select --install

Windows

Use MinGW-w64 or MSYS2
Or integrate with Visual Studio project

Embedded Systems

Library is designed to work on resource-constrained systems
No heap allocations in core crypto functions
Stack usage is predictable and bounded

API Reference

Initialization

int nostr_init(void);                    // Initialize library
void nostr_cleanup(void);                // Cleanup resources
const char* nostr_strerror(int error);   // Get error string

Key Generation

int nostr_generate_keypair(unsigned char* private_key, unsigned char* public_key);
int nostr_generate_mnemonic_and_keys(char* mnemonic, size_t mnemonic_size, 
                                     int account, unsigned char* private_key, 
                                     unsigned char* public_key);
int nostr_derive_keys_from_mnemonic(const char* mnemonic, int account,
                                    unsigned char* private_key, unsigned char* public_key);

Event Creation

cJSON* nostr_create_text_event(const char* content, const unsigned char* private_key);
cJSON* nostr_create_profile_event(const char* name, const char* about, 
                                  const unsigned char* private_key);
int nostr_sign_event(cJSON* event, const unsigned char* private_key);

Utilities

void nostr_bytes_to_hex(const unsigned char* bytes, size_t len, char* hex);
int nostr_hex_to_bytes(const char* hex, unsigned char* bytes, size_t len);
int nostr_key_to_bech32(const unsigned char* key, const char* hrp, char* output);
nostr_input_type_t nostr_detect_input_type(const char* input);

Error Handling

All functions return standardized error codes:

NOSTR_SUCCESS (0): Operation successful
NOSTR_ERROR_INVALID_INPUT (-1): Invalid parameters
NOSTR_ERROR_CRYPTO_FAILED (-2): Cryptographic operation failed
NOSTR_ERROR_MEMORY_FAILED (-3): Memory allocation failed
NOSTR_ERROR_IO_FAILED (-4): File I/O operation failed
NOSTR_ERROR_NETWORK_FAILED (-5): Network operation failed

Security Considerations

Private Key Handling: Always clear private keys from memory when done
Random Number Generation: Uses /dev/urandom on Unix systems
Memory Safety: All buffers are bounds-checked
Constant-Time Operations: Critical crypto operations are timing-attack resistant

Testing Your Integration

Use the provided examples to verify your integration:

# Test key generation
./examples/simple_keygen

# Test mnemonic functionality
./examples/mnemonic_generation

# Test event creation
./examples/text_event

# Test all functionality
./examples/utility_functions

Support and Documentation

See examples/ directory for comprehensive usage examples
Check SELF_CONTAINED_CRYPTO.md for cryptographic implementation details
Review CROSS_PLATFORM_GUIDE.md for platform-specific notes
All functions are documented in nostr_core.h

License

This library is designed to be freely integrable into other projects. Check the individual file headers for specific licensing information.

Quick Start: Copy nostr_core.h, nostr_core.c, nostr_crypto.h, nostr_crypto.c, and the cjson/ folder to your project, then compile with -lm. That's it!

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