A WebCrypto polyfill that "smooths out" the rough-edges in existing User Agent implementations.

Usage no npm install needed!

<script type="module">
  import webcryptoLiner from 'https://cdn.skypack.dev/webcrypto-liner';



license npm version test


A polyfill for WebCrypto that "smooths out" the rough-edges in existing User Agent implementations.

Though WebCrypto is well supported across browsers, several browsers still have prefixed and buggy implementations. Additionally, they do not always support the same algorithms, for example, Edge does not support SHA1 or ECC while both Firefox and Chrome do.

NOTE: If you are not familiar with how to use the various capabilities of WebCrypto see this great example page.

Browsers support

IE / Edge
last 2 versions last 2 versions last 2 versions last 2 versions


webcrypto-liner is a wrapper for WebCrypto designed to address these issues, at the same time it was designed to be modular so that it can also be used for testing the addition of new algorithms to WebCrypto in the future.

Intentionally webcrypto-liner does not implement any cryptography though it does consume libraries that do. We strongly recommend you read "What’s wrong with in-browser cryptography?" before using this library.

The libraries webcrypto-liner relies on include:

Package Description Size Optional
asmcrypto.js A performant JavaScript implementation of popular cryptographic utilities with performance in mind. 131 KB Yes
elliptic Fast Elliptic Curve Cryptography in plain javascript 130 KB Yes
webcrypto-core A input validation layer for WebCrypto polyfills 1 25 KB No

1 This library is compiled into webcrypto-liner.

webcrypto-liner will always try to use a native implementation of webcrypto, or a prefixed version of webcrypto, before it falls back to a Javascript implementation of a given algorithm. We have no control over the corresponding implementation and what it does, for example, it may not use window.crypto.getRandomValues even if it is available and the mechanism it uses to gather randomness may be both insecure and weak.

We have done no security review or take a position on the security of these third-party libraries. YOU HAVE BEEN WARNED.

To keep webcrypto-liner as small as possible (right now it is ~11kb without dependencies) it was designed to be modular, so if you do not need ECC support, do not include elliptic as a dependency and it will not be loaded.

If you do not load any of the dependencies that provide cryptographic implementations webcrypto-liner will work as an interoperability layer, very similar to webcrypto-shim.

webcrypto-liner supports the following algorithms and key lengths:

Capability Details
Encryption/Decryption RSA-OAEP, DES-CBC1, DES-EDE3-CBC1, AES-ECB 1, AES-CBC, AES-ECB and AES-GCM
Sign/Verify RSA-PSS, RSASSA_PKCS1-v1_5 and ECDSA
Hash SHA-1, and SHA-256, SHA-512
Derive Key/Bits ECDH, PBKDF2
ECC Curves P-256, P-384, P-521, and K-2562 (secp256k1)
RSA Key Lengths 1024, 2048, 3072, and 4096
AES Key Lengths 128, 192 and 256

1 Mechanism is not defined by the WebCrypto specifications. Use of mechanism in a safe way is hard, it was added for the purpose of enabling interoperability with an existing system. We recommend against its use unless needed for interoperability.

2 K-256 (secp256k1) curve is not defined by the WebCrypto specifications.

You can see the webcrypto-liner in use in the pv-webcrypto-tests page.


  <!-- Crypto providers are optional -->
  <script src="https://cdnjs.cloudflare.com/ajax/libs/babel-polyfill/7.7.0/polyfill.min.js"></script>
  <script src="https://cdnjs.cloudflare.com/ajax/libs/asmCrypto/2.3.2/asmcrypto.all.es5.min.js"></script>
  <script src="https://cdn.rawgit.com/indutny/elliptic/master/dist/elliptic.min.js"></script>
  <!-- Crypto -->
  <script src="webcrypto-liner.shim.js"></script>
    crypto.subtle.generateKey({name: "AES-GCM", length: 192}, true, ["encrypt", "decrypt"])
        return crypto.subtle.encrypt({
            name: "AES-GCM", 
            iv: new Uint8Array([1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16]),
            tagLength: 128
          }, key, new Uint8Array([1,2,3,4,5]))
        console.log(new Uint8Array(enc));
        console.log(err.message); // Chrome throws: 192-bit AES keys are not supported



npm install typescript --global


The module has been designed to be useful in ES6 and ES5 projects. The default is ES5 with commonjs, to install and build you would run:

npm install
npm run build


  • Do I need to use a promise library? - No, not if your browser supports promises.
  • Do I need to include asmcrypto.js? No, not unless you want to use the algorithms it exposes.
  • Do I need to include elliptic.js? No, not unless you want to use the algorithms it exposes.
  • How are random numbers generated? We use two libraries for crypto operations in Javascript, asymcrypto and ellipticjs both rely on window.crypto.getRandomValues where available. asymcrypto also has a fallback mechanism where it generates its own random numbers if not present.
  • How big is the total package? Right now, if you include all optional dependencies (minfied) the package is ~300 KB, if you include only ECC or only RSA support that is lowered to about 180 KB. Additionally you will see GZIP compression provide about 30% savings above and beyond that. If you use webcrypto-liner as just an interopability shim and do not use any of the optional third-party libraries it will be under 44 KB in size.
  • Will it work in Node? No. It is compiles to pure Javascript but uses the window object so it wont work in Node at this time. With some minor changes it should also be able to work in Node also but you really should be using node-webcrypto-ossl on Node instead.