PrivateKeySigner

PrivateKeySigner

The PrivateKeySigner is the default implementation of the NostrSigner interface provided by the @contextvm/sdk. It is a straightforward and easy-to-use signer that operates directly on a raw private key provided as a hexadecimal string.

Overview

The PrivateKeySigner is designed for scenarios where the private key is readily available in the application’s environment. It handles all the necessary cryptographic operations locally, including:

• Deriving the corresponding public key.
• Signing Nostr events.
• Encrypting and decrypting messages using NIP-44.

constructor(privateKey: string)

The constructor takes a single argument:

• privateKey: A hexadecimal string representing the 32-byte Nostr private key.

When instantiated, the PrivateKeySigner will immediately convert the hex string into a Uint8Array and derive the public key, which is then cached for future calls to getPublicKey().

Usage Example

import { PrivateKeySigner } from "@contextvm/sdk";

// Replace with a securely stored private key
const privateKeyHex = "your-32-byte-private-key-in-hex";

const signer = new PrivateKeySigner(privateKeyHex);

// You can now pass this signer instance to a transport
const transportOptions = {
  signer: signer,
  // ... other options
};

Key Methods

The PrivateKeySigner implements all the methods required by the NostrSigner interface.

async getPublicKey(): Promise<string>

Returns a promise that resolves with the public key corresponding to the private key provided in the constructor.

async signEvent(event: UnsignedEvent): Promise<NostrEvent>

Takes an unsigned Nostr event, signs it using the private key, and returns a promise that resolves with the finalized, signed NostrEvent.

nip44

The PrivateKeySigner also provides a nip44 object that implements NIP-44 encryption and decryption. This is used internally by the transports when encryption is enabled, and it allows the decryptMessage function to work seamlessly with this signer.

• encrypt(pubkey, plaintext): Encrypts a plaintext message for a given recipient public key.
• decrypt(pubkey, ciphertext): Decrypts a ciphertext message received from a given sender public key.

Security Considerations

While the PrivateKeySigner is convenient, it requires you to handle a raw private key directly in your application code. It is crucial to manage this key securely. Avoid hard-coding private keys in your source code. Instead, use environment variables or a secure secret management system to load the key at runtime.

For applications requiring a higher level of security, consider creating a custom signer that interacts with a hardware wallet or a remote signing service.

Next Steps

• Learn how to build a custom signer: Custom Signer Development