Function encryptMediaFile

Encrypts a media file for sharing in a Marmot group message (MIP-04 v2).

Uses ChaCha20-Poly1305 AEAD with a randomly generated nonce. The associated data (AAD) binds the scheme version, file hash, MIME type, and filename to prevent metadata tampering.

Typical usage:

import { sha256 } from "@noble/hashes/sha2";
import { bytesToHex } from "@noble/hashes/utils";
import { createImetaTagForAttachment } from "applesauce-common/helpers";

const attachment: Mip04MediaAttachment = {
  sha256: bytesToHex(sha256(fileBytes)),
  type: "image/jpeg",
  filename: "photo.jpg",
  nonce: "",          // filled by encryptMediaFile
  version: MIP04_VERSION,
};
const fileKey = await deriveMip04FileKey(clientState, ciphersuite, attachment);
const { encrypted, attachment: filled } = encryptMediaFile(fileBytes, fileKey, attachment);
// Upload `encrypted` to Blossom, then:
const imetaTag = createImetaTagForAttachment({ ...filled, url: blossomUrl });
Copy