A privacy-first web-based period tracker?

Is it even possible?

User Benedicte

Developer Benedicte

Don't be evil

vs.

Can't be evil

Thank you Jeffrey Goldberg!

@jpgoldberg on Twitter

Caveat

Encryption

Cyphertext

KEY

Plaintext

Entropy

A long random sequence of characters has high entropy, a short human memorable password has low entropy.

Encryption in the browser

  const key = await window.crypto.subtle.generateKey(
    {
      name: "AES-GCM",
      length: 256
    },
    true,
    ["encrypt", "decrypt"]
  );

Key generation

AES-GCM

Advanced Encryption Standard
with Galois Counter Mode

  const note = "A very secret note";
  const noteBuffer = new TextEncoder("utf-8").encode(note);

  const nonce = window.crypto.getRandomValues(new Uint8Array(12));

  const cyphertext = await window.crypto.subtle.encrypt(
    {
      name: "AES-GCM",
      iv: nonce
    },
    key,
    noteBuffer
  );

Encryption

   const plaintext = await window.crypto.subtle.decrypt(
    {
      name: "AES-GCM",
      iv: nonce
    },
    key,
    cyphertext
  );

  const decoder = new TextDecoder("utf-8")
  const decryptedNote = decoder.decode(new Uint8Array(plaintext))

  console.log(decryptedNote); // A very secret note

Decryption

Local Storage

  const password = "The user's secret password"
  const enc = new TextEncoder();

  const passwordAsKey = await window.crypto.subtle.importKey(
    "raw",
    enc.encode(password),
    {name: "PBKDF2"},
    false,
    ["deriveBits", "deriveKey"]
  );

Import key

PBKDF2

Password-Based Key Derivation Function 2

  const salt = window.crypto.getRandomValues(new Uint8Array(12));

  const key = await window.crypto.subtle.deriveKey(
    {
      name: "PBKDF2",
      salt: salt,
      iterations: 100000,
      hash: "SHA-256"
    },
    passwordAsKey,
    { name: "AES-GCM", length: 256},
    true,
    [ "encrypt", "decrypt" ]
  );

Derive key

Password

Salt

Cyphertext

Key

Plaintext

Encryption

Password

Salt

Plaintext

Key

Cyphertext

Decryption

The cloud

End-to-end encryption

Can I use a traditional BaaS

The challenge with traditional authentication

Secure Remote Password

Password

Salt

Cyphertext

Key

Plaintext

Encryption

Password

Salt

Plaintext

Key

Cyphertext

Decryption

Sharing

Cyphertext

KEY

Plaintext

KEY

Cyphertext

KEY

Plaintext

KEY

Cyphertext

Public

KEY

Plaintext

Private

KEY

const keyPair = window.crypto.subtle.generateKey(
  {
    name: "RSA-OAEP",
    modulusLength: 4096,
    publicExponent: new Uint8Array([1, 0, 1]),
    hash: "SHA-256"
  },
  true,
  ["encrypt", "decrypt"]
);

Key generation

Password

Salt

Encrypted
Private KEY

Key

Private
KEY

Blockstack

Is it possible?

Thank you!

Twitter: @raae

Instagram: @raae.codes