Utils

The Utils module provides low-level cryptographic functions and utilities for advanced use cases.

Encryption Functions

deriveECDHSecret

Derives a shared ECDH secret for encryption between two parties.

async function deriveECDHSecret(
  privateKey: `0x${string}`,
  publicKey: `0x${string}`
): Promise<Uint8Array>

Parameters

• privateKey: 0x${string} - Your private key
• publicKey: 0x${string} - Other party's public key (compressed or uncompressed)

Returns

Promise resolving to SHA-256 hashed shared secret (32 bytes)

Example

import { deriveECDHSecret } from '@moki-chat/core/utils'

const myPrivateKey = "0x..."
const theirPublicKey = "0x04..."

const sharedSecret = await deriveECDHSecret(myPrivateKey, theirPublicKey)
console.log(sharedSecret) // Uint8Array(32)

---

encryptWithECDHSecret

Encrypts content using AES-GCM with a shared secret.

async function encryptWithECDHSecret(
  sharedSecret: Uint8Array,
  content: string
): Promise<string>

Parameters

• sharedSecret: Uint8Array - Derived ECDH shared secret (32 bytes)
• content: string - Plain text to encrypt

Returns

Promise resolving to encrypted hex string: IV (12 bytes) + AuthTag (16 bytes) + Ciphertext

Example

import {
  deriveECDHSecret,
  encryptWithECDHSecret
} from '@moki-chat/core/utils'

const secret = await deriveECDHSecret(myPrivateKey, theirPublicKey)
const encrypted = await encryptWithECDHSecret(secret, "Secret message")

console.log(encrypted) // 0x...

Encryption Details

• Algorithm: AES-GCM
• Key: Shared secret (32 bytes)
• IV: Random 12 bytes
• Tag Length: 128 bits (16 bytes)
• Output Format: Hex string with IV + Tag + Ciphertext

---

decryptWithECDHSecret

Decrypts content encrypted with AES-GCM.

async function decryptWithECDHSecret(
  sharedSecret: Uint8Array,
  encryptedHex: string
): Promise<string>

Parameters

• sharedSecret: Uint8Array - Derived ECDH shared secret (32 bytes)
• encryptedHex: string - Encrypted hex string (from encryptWithECDHSecret)

Returns

Promise resolving to decrypted plain text

Example

import {
  deriveECDHSecret,
  decryptWithECDHSecret
} from '@moki-chat/core/utils'

const secret = await deriveECDHSecret(myPrivateKey, theirPublicKey)
const decrypted = await decryptWithECDHSecret(secret, encryptedHex)

console.log(decrypted) // "Secret message"

Throws

• Invalid encrypted data format
• Authentication tag verification failed
• Decryption errors

---

Public Key Functions

compressPublicKey

Compresses an uncompressed secp256k1 public key.

function compressPublicKey(
  uncompressedKey: `0x${string}`
): `0x${string}`

Parameters

• uncompressedKey: 0x${string} - Uncompressed public key (65 bytes: 0x04 + X + Y)

Returns

Compressed public key (33 bytes: 0x02/0x03 + X)

Example

import { compressPublicKey } from '@moki-chat/core/utils'

const uncompressed = "0x04..." // 65 bytes
const compressed = compressPublicKey(uncompressed)

console.log(compressed.length) // 66 (33 bytes * 2 + 2 for 0x)

---

decompressPublicKey

Decompresses a compressed secp256k1 public key.

function decompressPublicKey(
  compressedKey: `0x${string}`
): `0x${string}`

Parameters

• compressedKey: 0x${string} - Compressed public key (33 bytes)

Returns

Uncompressed public key (65 bytes: 0x04 + X + Y)

Example

import { decompressPublicKey } from '@moki-chat/core/utils'

const compressed = "0x02..." // 33 bytes
const uncompressed = decompressPublicKey(compressed)

console.log(uncompressed.length) // 130 (65 bytes * 2 + 2 for 0x)
console.log(uncompressed.startsWith('0x04')) // true