about_cryptography.md

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About the cryptography

This plugin uses the sha256 and pbkdf2 algorithms for generating a key from your password. The key is a 32 char Hash. And for encryption and decryption of your docs the AES-GCM algorithm gets used.

What is encrypted

Hoodie, CouchDB and PouchDB need _id, _rev, _deleted, _attachments and _conflicts to function. They and the content of the hoodie object, are not encrypted! Everything else goes through JSON.stringify and gets encrypted.

This includes all fields of old documents. Those fields will then get deleted!

Please be aware, that the _id of a doc is not encrypted! Don't store important or personal information in the _id!

Derive key from password and salt

var pbkdf2 = require('native-crypto/pbkdf2')
var randomBytes = require('randombytes')

async function deriveKey (password) {
  const doc = await hoodie.store.find('hoodiePluginCryptoStore/salt')

  const digest = 'sha256'
  const iterations = 100000
  const salt = doc.salt != null && typeof doc.salt === 'string' && doc.salt.length === 32
    ? doc.salt
    : randomBytes(16).toString('hex')

  const key = await pbkdf2(password, Buffer.from(salt, 'hex'), iterations, 256 / 8, digest)

  return {
    key: key,
    salt: salt
  }
}

Encrypt a document

var encrypt = require('native-crypto/encrypt')
var randomBytes = require('randombytes')

var ignore = [
  '_id',
  '_rev',
  '_deleted',
  '_attachments',
  '_conflicts',
  'hoodie'
]

async function encryptDoc (key, doc) {
  var nonce = randomBytes(12)
  var outDoc = {
    nonce: nonce.toString('hex')
  }

  ignore.forEach(function (key) {
    outDoc[key] = doc[key]
    delete doc[key]
  })

  var data = JSON.stringify(doc)
  const response = await encrypt(key, nonce, data, Buffer.from(outDoc._id))

  outDoc.tag = response.slice(-16).toString('hex')
  outDoc.data = response.slice(0, -16).toString('hex')

  return outDoc
}

Decrypt a document

var decrypt = require('native-crypto/decrypt')

var ignore = [
  '_id',
  '_rev',
  '_deleted',
  '_attachments',
  '_conflicts',
  'hoodie'
]

async function decryptDoc (key, doc) {
  var data = Buffer.from(doc.data, 'hex')
  var tag = Buffer.from(doc.tag, 'hex')
  var encryptedData = Buffer.concat([data, tag])

  var nonce = Buffer.from(doc.nonce, 'hex')
  var aad = Buffer.from(doc._id)

  const outData = await decrypt(key, nonce, encryptedData, aad)
  var out = JSON.parse(outData)

  ignore.forEach(function (key) {
    var ignoreValue = doc[key]

    if (ignoreValue !== undefined) {
      out[key] = ignoreValue
    }
  })

  return out
}