mesh-sdk/src/seal/index.ts

// Sealing to one recipient (novox/hq ADR 0183, ADR 0206): X25519 for the agreement, HKDF-SHA256 for the
// key, AES-256-GCM for the box. The TypeScript twin of the Go package `go/seal`, byte for byte: the same
// fixtures prove both. A box is `{ v: 1, eph, iv, tag, ct }`; keys travel as PEM (SPKI public, PKCS #8
// private).

import { generateKeyPairSync, randomBytes } from "node:crypto";
import { sealWith, open, VERSION, type SealedBox } from "./box.js";

export { open, VERSION, type SealedBox };

/** A recipient's keypair as the two PEM strings it is kept and sent as. */
export interface KeyPair {
  readonly publicKey: string;
  readonly privateKey: string;
}

/** A fresh X25519 keypair, PEM-encoded. */
export function generateKeyPair(): KeyPair {
  const { publicKey, privateKey } = generateKeyPairSync("x25519");
  return {
    publicKey: publicKey.export({ format: "pem", type: "spki" }) as string,
    privateKey: privateKey.export({ format: "pem", type: "pkcs8" }) as string,
  };
}

/** Seal plaintext to the recipient's PEM public key, with a fresh one-time key and iv. */
export function seal(plaintext: string, recipientPem: string): SealedBox {
  return sealWith(plaintext, recipientPem, generateKeyPairSync("x25519").privateKey, randomBytes(12));
}