Module @trevixal/extension-security

@trevixal/extension-security

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Features

Password-encrypted documents with expiry
Encrypted storage and copy restrictions
2.9 kB minified and gzipped, with TypeScript types in the package

Password-encrypted documents, expiry, an encrypted storage wrapper, and copy/print restrictions.

npm install @trevixal/extension-security

Encrypting a document

import { encryptDocument, decryptDocument, WrongPasswordError } from '@trevixal/extension-security'

const envelope = await encryptDocument(editor.getJSON(), password, {
  expiresAt: Date.now() + 7 * 864e5,
})

try {
  const { payload } = await decryptDocument(envelope, password)
  editor.setContent(payload)
} catch (error) {
  if (error instanceof WrongPasswordError) askAgain()
}

The envelope is plain JSON ({ format, version, kdf, iterations, salt, iv, cipher, data, expiresAt }) so it stores and travels like any other document. The key is stretched with PBKDF2-SHA256 (310,000 rounds by default) and the content sealed with AES-GCM, both through the browser's own WebCrypto. There is no cipher code here to audit or keep current, which is the point.

The iteration count travels in the envelope, so a ceiling of ten million is enforced on what one may ask for: without it, a hostile file could ask for a number that hangs the tab.

An encrypted key-value store

import { createEncryptedStorage, createWebStorage } from '@trevixal/extension-security'

const vault = createEncryptedStorage(createWebStorage(localStorage, 'app:'), password)

A drop-in KeyValueStorage, so autosave and the document workspace can write through it unchanged and a draft on disk is unreadable without the password. The password may be an async getter, for hosts that prompt lazily.

Restrictions

import { applyRestrictions, restrictionsAllow } from '@trevixal/extension-security'

const release = applyRestrictions(
  editor,
  { copy: true, print: true },
  { onBlocked: (action) => say(`${action} is blocked`) },
)

copy, cut, paste, print, download and contextMenu. Print also swallows the shortcut, reports beforeprint, and injects a print-media rule that blanks the surface if the dialog is opened another way.

These keep an honest user honest. They are not a confidentiality control, anything rendered in a browser can be read out of it, and should not be sold as one.

Expiry

isExpired(expiresAt) and describeExpiry(expiresAt). The description rounds down: forty-five days reads as "in 1 month", never "in 2 months". This string tells someone when a document stops opening, and the failure mode of overstating it is losing access while believing there was time.