The Web Crypto API

Katy Moe

About me

 

JavaScript Engineer at Kahoot!


mathematician


digital rights enthusiast

Introduction

1. intro to crypto

2. why we need web crypto

3. how to use the API

4. the spec

The next twenty minutes

Intro to crypto

Crypto is about keeping secrets

THIS IS A SECRET MESSAGE TO BE XORED WITH A SECRET KEY TO PRODUCE A CIPHERTEXT. THIS IS CALLED ENCRYPTION.

plaintext

HSD0472B1VX8V5BLR02010DHCV8B6W25N6KGBJV9SYS9C6 5BOG98383BY398Y98FR9GBBV2964783NHJFIFNJB90N7480

9GFGJFHGD76FVB2C1SD1SA2P408G00ZXBVB302479DHFJHAA83T1VSNXYBV8B9CBVA7F5395GKVBQ9X8GK2N1V49V09

+

=

key

ciphertext

Symmetric cryptography

H487SBFK593OSFH0N8BLSK4278SBTOB9P

Alice

Alice

Alice's key

Alice's key

my secret

my secret

Public key cryptography

H487SBFK593OSFH0N8BLSK4278SBTOB9P

Alice

Bob

Bob's public key

Bob's private key

Hello, Bob!

Hello, Bob!

Randomness

Cryptographically
Secure

 

Pseudo-
Random

 

Number
Generator

 

Math.random()

Random.org

?

?

?

?

?

?

The Web Crypto API: crypto in the browser

But we already have TLS

browser

server

browser

TLS

TLS

plaintext

plaintext

plaintext

link layer

internet/IP layer

transport layer

application layer

TLS

Web Crypto API

 

 

JS || GTFO

// 1. create key buffer
const keyArrayBuffer = new Uint8Array([0x00, 0x11, 0x22, 0x33, 
                                       0x44, 0x55, 0x66, 0x77, 
                                       0x88, 0x99, 0xaa, 0xbb, 
                                       0xcc, 0xdd, 0xee, 0xff]);

// 2. encode plaintext
const encoder = new TextEncoder('utf-8');
const plaintext = 'Alice has a secret';
const encodedPlaintext = encoder.encode(plaintext);

// 3. import raw key
window.crypto.subtle.importKey(
  'raw', keyArrayBuffer, {
  name: 'AES-GCM'
}, false, ['encrypt', 'decrypt']
).then(function(key) {
  // 4. generate random IV
  const iv = window.crypto.getRandomValues(new Uint8Array(12));

  // 5. encrypt
  return window.crypto.subtle.encrypt({
    name: 'AES-GCM',
    iv
  }, key, encodedPlaintext);
}).then(function(ciphertext) {
  console.log(new Uint8Array(ciphertext));
});

5. encrypt

1. create key buffer

2. encode plaintext

3. import raw key

4. generate random IV

Symmetric encryption

window.crypto.getRandomValues
window.crypto.subtle

1. create key buffer

const keyArrayBuffer = new Uint8Array([0x00, 0x11, 0x22, 0x33, 
                                       0x44, 0x55, 0x66, 0x77, 
                                       0x88, 0x99, 0xaa, 0xbb, 
                                       0xcc, 0xdd, 0xee, 0xff]);

2. encode plaintext

const encoder = new TextEncoder('utf-8');

const plaintext = 'Alice has a secret';

const encodedPlaintext = encoder.encode(plaintext);

3. import raw key

// def: keyArrayBuffer

window.crypto.subtle.importKey(
  'raw', 
  keyArrayBuffer, 
  { name: 'AES-GCM' }, 
  false, 
  ['encrypt', 'decrypt']
);

4. generate random IV

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

5. encrypt

// def: encodedPlaintext, iv, key

window.crypto.subtle.encrypt({
    name: 'AES-GCM',
    iv
  }, key, encodedPlaintext);
// 1. create key buffer
const keyArrayBuffer = new Uint8Array([0x00, 0x11, 0x22, 0x33, 
                                       0x44, 0x55, 0x66, 0x77, 
                                       0x88, 0x99, 0xaa, 0xbb, 
                                       0xcc, 0xdd, 0xee, 0xff]);

// 2. encode plaintext
const encoder = new TextEncoder('utf-8');
const plaintext = 'Alice has a secret';
const encodedPlaintext = encoder.encode(plaintext);

// 3. import raw key
window.crypto.subtle.importKey(
  'raw', keyArrayBuffer, {
  name: 'AES-GCM'
}, false, ['encrypt', 'decrypt']
).then(function(key) {
  // 4. generate random IV
  const iv = window.crypto.getRandomValues(new Uint8Array(12));

  // 5. encrypt
  return window.crypto.subtle.encrypt({
    name: 'AES-GCM',
    iv
  }, key, encodedPlaintext);
}).then(function(ciphertext) {
  console.log(new Uint8Array(ciphertext));
});

The spec

Working Draft

Candidate Recommendation

Proposed Recommendation

W3C Recommendation

Web Crypto API

Browser support

Opinions on the API

1. Why so many params?

2. How do we discover

algorithms?

3. Why not recommend algorithms?

The Web Crypto API: crypto in the browser

Thank you

Kahoot! is hiring!

Resources

Opinions

The Web Crypto API

By Katharine Moe

The Web Crypto API

A talk on the Web Crypto API to be given at Front-End London on Thursday 29th October 2015.

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