Encryptor

A TypeScript utility for ECDH key exchange, AES-256-CBC encryption/decryption, and shared-secret computation between a browser and an app platform.

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Installation

JSR (Deno / Bun / Node.js)

deno add jsr:@cypriot/encryptor
bunx jsr add @cypriot/encryptor
npx jsr add @cypriot/encryptor

npm

npm install @cypriotunknown/encryptor

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Features

• Generate ECDH key pairs (P-256 curve)
• Import/export keys for both browser (JWK) and app (SPKI/PKCS8) platforms
• Compute shared secrets via ECDH + SHA-256
• AES-256-CBC symmetric encryption and decryption
• Random digit generation (e.g. OTP codes)
• Works in Node.js 18+, Bun, and modern browsers (uses crypto.subtle)

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Usage

1. Generate keys

import Encryptor from '@cypriot/encryptor';

// Browser platform (uses JWK)
const browserKeys = await Encryptor.generateKeys({ platform: "browser" });

// App platform (uses PKCS8/SPKI)
const appKeys = await Encryptor.generateKeys({ platform: "app" });

Returns a SecurityKeysOutput:

{
  privateKeyString: string; // serialized private key — never share this
  publicKeyString: string;  // serialized public key — share with the other party
  privateKey: CryptoKey;    // native CryptoKey, ready to use directly
}

2. Import a key from a string

// Re-import a stored app private key
const privateKey = await Encryptor.generateCryptoKeyFromBase64({
  platform: "app",
  base64KeyString: appKeys.privateKeyString,
  returnKey: "private",
});

// Import a peer's browser public key
const publicKey = await Encryptor.generateCryptoKeyFromBase64({
  platform: "browser",
  base64KeyString: browserKeys.publicKeyString,
});

3. Compute a shared secret

const sharedSecret = await Encryptor.computeSecret({
  clientPublicKeyBase64: browserKeys.publicKeyString,
  privateKey: appPrivateKey,
  platform: "app",
});

Returns a Base64-encoded, SHA-256-hashed shared secret.

4. Generate random digits (OTP)

const otp = Encryptor.generateRandomDigits({ maxDigits: 6 });
console.log(otp); // e.g. "482031"

5. Encrypt and decrypt

const encrypted = await Encryptor.encryptContent({
  content: JSON.stringify({ message: "Hello World" }),
  secret: sharedSecret,
  platform: "app",
});

const decrypted = await Encryptor.decryptContent({
  content: encrypted,
  secret: sharedSecret,
  platform: "app",
});

console.log(decrypted); // {"message":"Hello World"}

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Supported Platforms

Platform	Key Format	Cipher Output	Typical Use Case
"browser"	JWK (JSON string)	Hex	Web clients using the Web Crypto API
"app"	SPKI / PKCS8 (Base64)	Base64	Mobile/desktop apps, Node.js/Bun backends

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Full Example

Two applications exchanging an encrypted message:

import Encryptor, { type EncryptorPlatform } from '@cypriot/encryptor';

const platform: EncryptorPlatform = "app";

const clientKeys = await Encryptor.generateKeys({ platform });
const serverKeys = await Encryptor.generateKeys({ platform });

// Each party computes the same shared secret from the other's public key
const sharedSecret = await Encryptor.computeSecret({
  clientPublicKeyBase64: clientKeys.publicKeyString,
  privateKey: serverKeys.privateKey,
  platform,
});

const encrypted = await Encryptor.encryptContent({
  content: JSON.stringify({ hello: "world" }),
  platform,
  secret: sharedSecret,
});

console.log(encrypted);
// { iv: "bBJXZLp5XIKF68Xcdu3Ecg==", hash: "FYrQAVSeDhk..." }

const decrypted = await Encryptor.decryptContent({
  content: encrypted,
  secret: sharedSecret,
  platform,
}).then(d => JSON.parse(d));

console.log(decrypted);
// { hello: "world" }

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Related Packages

Language	Package
Swift	SwiftEncryptor — iOS 15+ / macOS 12+ / tvOS 15+ / watchOS 8+, built on CryptoKit and CommonCrypto
Go	encryptor-go — go get github.com/CypriotUnknown/encryptor-go

All three implementations share the same P-256 curve, SHA-256 secret digest, AES-256-CBC cipher, and "app"/"browser" platform conventions, so any pair can interoperate directly.

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License

MIT