svelte-subtlecrypto-store

This module provides an encrypted writable store for Svelte using the Crypto and
SubtleCrypto APIs.

This is mainly a proof-of-concept, and is largely based on the documentation
found at Mozilla Developer Network Web Docs:

- Crypto
- SubtleCrypto
- Base64

Motivation

I'm not a cryptographer. I don't write crypto. They say: don't write crypto, but
when you do, learn why you shouldn't have.

On top of it, I'm doing it to learn JavaScript and Svelte. This should be enough
for you not to use this module for anything else but what is stated in the
introduction: a proof-of-concept, or just fun.

Security details

Encryption is done with AES-256-GCM and key derivation with PBKDF2 with SHA-384.
The Salt and Initialization Vector are generated with Crypto.getRandomValues.
There are only three configurable options:

- The number of iterations for PBKDF2.
- The length of the salt for PBKDF2.
- The length of the Initialization Vector for AES-256-GCM.

All these values have very well documented defaults, and you can override any or
all of them passing the opts parameter. Example:

``import { writable } from 'svelte/store'; import { subtleCryptoStore } from 'svelte-subtlecrypto-store';

const backend = writable(''); const store = subtleCryptoStore(window.crypto, backend, 'my super pass', { iterations: 10000, saltLength: 16, ivLength: 64 });`

NOTE: these options are very strictly expected to be finite, positive integer values of typenumber. If you supply something like '16' or 16.1that value will be dropped and a default used. Use predefined constants, sanitize your input or check the returnedoptionsmember, which contains the parameters being used.

`Compatibility`

Source code is written in typescript targetting es2016. By then Crypto and SubtleCrypto APIs were already available in most major browsers.

Crypto and SubtleCrypto APIs are only available in a Secure Context. For browsers, this means that theWindow or Workerhave an HTTPS origin, and if the window belongs to aniframe, then all its ancestors are also delivered through HTTPS. There are other cases as well, you can read the linked document for more information. At runtime, the global and readonly property isSecureContext can be used to easily detect the availability of these features, so if it returnstrue` then you should have access to these APIs.

Motivation

I'm not a cryptographer. I don't write crypto. They say: don't write crypto, but
when you do, learn why you shouldn't have.

Security details

- The number of iterations for PBKDF2.
- The length of the salt for PBKDF2.
- The length of the Initialization Vector for AES-256-GCM.

All these values have very well documented defaults, and you can override any or
all of them passing the opts parameter. Example:


import { writable } from 'svelte/store';
import { subtleCryptoStore } from 'svelte-subtlecrypto-store';

const backend = writable('');
const store = subtleCryptoStore(window.crypto, backend, 'my super pass', {
    iterations: 10000,
    saltLength: 16,
    ivLength: 64
});

NOTE: these options are very strictly expected to be finite, positive
integer values of type

number. If you supply something like '16' or 16.1


that value will be dropped and a default used. Use predefined constants,
sanitize your input or check the returned

options

 member, which contains the
parameters being used.

Compatibility

Source code is written in typescript targetting es2016. By then Crypto and
SubtleCrypto APIs were already available in most major browsers.

Crypto and SubtleCrypto APIs are only available in a
Secure Context.
For browsers, this means that the

Window or Worker

 have an HTTPS origin, and
if the window belongs to an

iframe

, then all its ancestors are also delivered
through HTTPS. There are other cases as well, you can read the linked document
for more information. At runtime, the global and readonly property
isSecureContext
can be used to easily detect the availability of these features, so if it
returns

true` then you should have access to these APIs.