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Web Cryptography API Polyfill
C++ C JavaScript Python Shell CSS
branch: master

README.md

Netflix WebCrypto (NfWebCrypto)

Netflix WebCrypto is a polyfill of the W3C Web Cryptography API, 22 April 2013 Editor's Draft, as a native Chrome PPAPI plugin. Unlike a javascript polyfill, the native implementation supports a stronger security model with no key material exposed to javascript. The goal is to make the Web Crypto Javascript API freely available to web developers for experimentation and use prior to its implementation by browser vendors.

Currently only Google Chrome / Chromium on linux amd64 is supported.

Features

NfWebCrypto does not implement the Web Crypto API in its entirety, due to limitations of browser plugin technology and initial focus on operations and algorithms most useful to Netflix. However, the existing feature set supports many typical and common crypto use cases targeted by the Web Crypto API.

Supported

  • Interfaces supported:
    • Key, KeyPair
    • KeyOperation
    • CryptoOperation
    • CryptoKeys
  • SubtleCrypto interface methods supported
    • encrypt, decrypt
    • sign, verify
    • generateKey
    • exportKey, importKey
    • wrapKey, unwrapKey* **
  • CryptoKeys interface methods supported
    • getKeyByName
  • Key formats supported
    • symmetric keys: raw and jwk (raw)
    • asymmetric keys: pkcs#8 (public), spki (private), and jwk (public only)
  • Algorithms supported
    • SHA-1, SHA-224, SHA-256, SHA-384, SHA-512: digest
    • HMAC SHA-256: sign, verify, importKey, exportKey, generateKey
    • AES-128 CBC w/ PKCS#5 padding: encrypt, decrypt, importKey, exportKey, generateKey
    • RSASSA-PKCS1-v1_5: sign, verify, importKey, generateKey
    • RSAES-PKCS1-v1_5: encrypt, decrypt, importKey, exportKey, generateKey
    • Diffie-Hellman: generateKey, deriveKey
    • RSA-OAEP: wrapKey, unwrapKey
    • AES-KW: wrapKey, unwrapKey
    • AES-GCM: encrypt, decrypt, importKey, exportKey, generateKey

*A special "Kds" NamedKey bound to the plugin binary and script origin can be used with (un)wrapKey to export/import opaque key representations for persistence in HTML5 local storage or equivalent.

**Wrap/Unwrap operations follow the Netflix KeyWrap Proposal and support protection of the JWE payload with AES128-GCM. It is be possible to wrap/unwrap the following key types: HMAC SHA-256 and AES-128 CBC.

Not Supported

  • The streaming/progressive processing model in not supported
  • Synchronous API's like getRandomValues() are not supported
  • Algorithm normalizing rules are not fully implemented

Moving forward, Netflix will continue to enhance this implementation and try to keep it as much in sync as possible with the latest draft Web Crypto API spec.

Requirements

Linux

  • Ubuntu 12.04 64-bit with build-essential, libssl-dev-1.0.1c or later, and cmake 2.8 or later
  • 64-bit Google Chrome / Chromium R22 or later (tested with R27)

Directory Tour

base/
    Common C++ source for both the plugin and crypto component.
cmake/
    Cmake toolchain files.
    Linux desktop builds use the linux system build tools and libs.
    Only 64-bit builds are supported for now.
crypto/
    C++ source for the crypto component. The contents of this directory is
    of primary interest to native devs; the entry point is the CadmiumCrypto
    class. This directory currently builds to an archive file.
crypto/test/
    Contains C++ gtest unit tests that exercise the CadmiumCrypto class
    interface. Not fleshed out yet and currently not built.
misc/
    Miscellaneous code to support development. Currently has code to run and
    debug the Chrome browser with the plugin properly registered.
plugin/
    C++ source of the PPAPI plugin. This code builds to shared library that
    is dl-loaded by the browser when the plugin is registered. It handles
    interfacing with the browser, bridging to the crypto thread, and decode/
    dispatch of JSON messages to and from the browser. Native devs will
    probably only be interested in the NativeBridge class here.
web/nfcrypto.js
    The javascript front-end for the plugin. The bottom level of this code
    handles the transport of JSON-serialized messages to and from the
    plugin, while the top level implements the W3C WebCrypto interface.
    Native devs will need to change the bottom level to match their bridge
    API. This source file borrows heavily from PolyCrypt (polycrypt.net)
web/test_qa.html
    The Jasmine HTML unit tests that exercise the javascript WebCrypto
    API exposed to the javascript client by nfcrypto.js.

How to Build

The following has been verified on Ubunutu 12.04. cmake 2.8 or later is required.

NOTE: The SYSTEM key mentioned above depends in part on a secret build-time key SECRET_SYSTEM_KEY that for example purposes is hard-coded in linux_common.cmake. Actual deployments must change this key.

$ mkdir buildDir
$ cd buildDir
$ cmake -DCMAKE_TOOLCHAIN_FILE=(repo)/cmake/toolchains/linux64.cmake -DCMAKE_BUILD_TYPE=[Debug|Release] (repo)
$ make -j<N>

Build Results

Browser plugin - This is registered and run within the Chrome browser.

(buildDir)/plugin/libnfwebcrypto.so
(buildDir)/plugin/nfwebcrypto.info

Native gtest unit test executable (if built). This is run from the command line.

(buildDir)/crypto/test/test

Native CadmiumCrypto archive. Native apps will link to this archive.

(buildDir)/crypto/libcadcrypto.a

How to run the Unit Tests

Chrome must be run with a special command line option to register the plugin. The easiest way to do this is to use the provided start.sh script, which employs the .info file generated by the build.

Make a directory and copy or symlink start.sh, libnfwebcrypto.so, and nfwebcrypto.info.

$ mkdir runNfWebCrypto
$ cd !$
$ ln -s (repo)/misc/desktop/start.sh
$ ln -s (buildDir)/plugin/libnfwebcrypto.so
$ ln -s (buildDir)/plugin/nfwebcrypto.info

The start.sh script depends on the chrome executable present at /opt/google/chrome/chrome. Edit the script if this is not true. Finally, start chrome and run the unit tests hosted on github by running the script.

$ ./start.sh

Note that there must not be any other chrome instance running in the system before the script is executed. Otherwise the action will be to just open a new tab on the existing instance without loading the plugin.

The unit tests will run automatically and all should pass.

Sample Code

Here are some examples of how to use the Web Cryptography API to perform typical crypto operations. These will work once the plugin is installed and enabled. More detailed usage examples may be found in the javascript unit tests.

The examples below use the following utility functions to convert between string and Uint8Array:

// string to uint array
function text2ua(s) {
    var ua = new Uint8Array(s.length);
    for (var i = 0; i < s.length; i++) {
        ua[i] = s.charCodeAt(i);
    }
    return ua;
}

// uint array to string
function ua2text(ua) {
    var s = '';
    for (var i = 0; i < ua.length; i++) {
        s += String.fromCharCode(ua[i]);
    }
    return s;
}

Compute SHA-1 hash

<script src='nfcrypto.js'></script>
<script>
    var cryptoSubtle = window.nfCrypto.subtle;
    var data = "This is some data to hash";    
    var op = cryptoSubtle.digest({ name: "SHA-1" }, text2ua(data));
    op.oncomplete = function (e) {
        window.alert("SHA-1 of \"" + data + "\": " + btoa(e.target.result));
    };
</script>

AES-CBC Encryption / Decryption

<script src='nfcrypto.js'></script>
<script>

    var cryptoSubtle = window.nfCrypto.subtle;
    var cleartext = "This is some cleartext to encrypt.";
    var key;
    var iv = new Uint8Array([0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
                             0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F]);
    var ciphertext;

    // generate a non-extractable 128-bit AES key
    function generateKey() {
        var genKeyOp = cryptoSubtle.generateKey(
            { name: "AES-CBC", params: { length: 128 } },
            false
        );
        genKeyOp.oncomplete = function (e) {
            key = e.target.result;
            encryptData();
        }
    }

    // encrypt cleartext to get ciphertext
    function encryptData() {
        var encOp = cryptoSubtle.encrypt({
            name: "AES-CBC",
            params: { iv: iv }
        }, key, text2ua(cleartext));
        encOp.oncomplete = function (e) {
            cipherText = e.target.result;
            decryptData();
        }
    }

    // decrypt ciphertext to get cleartext
    function decryptData() {
        var encOp = cryptoSubtle.decrypt({
            name: "AES-CBC",
            params: { iv: iv }
        }, key, cipherText);
        encOp.oncomplete = function (e) {
            var cleartext2 = ua2text(e.target.result);
            if (cleartext2.valueOf() == cleartext.valueOf()) {
                window.alert("Round-trip encryption/decryption works!");
            }
        }
    }

    generateKey();

</script>

Sign / Verify Data with HMAC SHA256

<script src='nfcrypto.js'></script>
<script>

    var cryptoSubtle = window.nfCrypto.subtle;
    var data = "This is some data to sign",
        hmacKey,
        signature;

    function generateKey() {
        var genOp = cryptoSubtle.generateKey({ name: "HMAC", params: { hash: {name: "SHA-256"} } });
        genOp.oncomplete = function (e) {
            hmacKey = e.target.result;
            signData();
        };
    }

    function signData() {
        var signOp = cryptoSubtle.sign(
            { name: "HMAC", params: { hash: "SHA-256" } },
            hmacKey,
            text2ua(data)
        );
        signOp.oncomplete = function (e) {
            signature = e.target.result;
            verifyData();
        };
    }

    function verifyData() {
        var verifyOp = cryptoSubtle.verify(
            { name: "HMAC", params: { hash: "SHA-256" } },
            hmacKey,
            signature,
            text2ua(data)
        );
        verifyOp.oncomplete = function (e) {
            if (e.target.result) {
                window.alert("Round-trip hmac sign/verify works!");
            }
        };
    }

    generateKey();

</script>

RSA Encryption / Decryption

<script src='nfcrypto.js'></script>
<script>

    var cryptoSubtle = window.nfCrypto.subtle;
    var clearText = "This is some data to encrypt";
    var pubKey, privKey;
    var cipherText;

    // generate a 1024-bit RSA key pair for encryption
    function generateKey() {
        var genOp = cryptoSubtle.generateKey({
            name: "RSAES-PKCS1-v1_5",
            params: {
                modulusLength: 1024,
                publicExponent: new Uint8Array([0x01, 0x00, 0x01]) // Fermat F4
            }
        }, false);
        genOp.oncomplete = function (e) {
            pubKey  = e.target.result.publicKey;
            privKey = e.target.result.privateKey;
            exportKey();
        }
    }

    // export the public key in SPKI format in order to send it to the peer
    function exportKey() {
        var exportOp = cryptoSubtle.exportKey("spki", pubKey);
        exportOp.oncomplete = function (e) {
            var pubKeySpki = e.target.result;
            // here you would send pubKeySpki to peer
            encryptData();
        }
    }

    // simulate peer encryption by encrypting clearText with the public key
    function encryptData() {
        var encryptOp = cryptoSubtle.encrypt(
            { name: "RSAES-PKCS1-v1_5" },
            pubKey,
            text2ua(clearText)
        );
        encryptOp.oncomplete = function (e) {
            cipherText = e.target.result;
            decryptData();
        }
    }

    // pretend the cipherText was received from the peer, and decrypt it
    // with the private key; should get the same clearText back
    function decryptData() {
        var decryptOp = cryptoSubtle.decrypt({ name: "RSAES-PKCS1-v1_5" }, privKey, cipherText);
        decryptOp.oncomplete = function (e) {
            var clearText2 = ua2text(e.target.result);
            if (clearText2.valueOf() == clearText.valueOf()) {
                window.alert("Round-trip RSA encrypt/decrypt successful!");
            }
        }
    }

    generateKey();

</script>
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