post-e-voting/source-code/scytl-cryptolib/cryptolib-js-digitalenvelope/README.md

Digital Envelope Module

This module defines the digital envelope API for Scytl's JavaScript cryptographic library. The starting point for using this module is the instantiation of a digital envelope service.

How to view, build and test the source code of this module

Start by git cloning the project comm/scytl-cryptolib from Stash.

The source code of this module will be found in the directory scytl-cryptolib/cryptolib-js-digitalenvelope/lib.

To build this module, change to the directory scytl-cryptolib/cryptolib-js-digitalenvelope and do the following:

npm install
--or--
mvn clean install -DskipTests

The unit tests of this module will be found in the directory scytl-cryptolib/cryptolib-js-digitalenvelope/spec. To run the tests, change to the directory scytl-cryptolib/cryptolib-js-digitalenvelope and do the following:

karma test
--or--
mvn test

To only run a chosen test suite, add an f in front of the corresponding describe statement. For example:

fdescribe('create a digital envelope generator/opener pair that should be able to', function()
...

To only run a chosen test, add an f in front of the corresponding it statement. For example:

fit('generate a digital envelope with a single public key and open the envelope with the corresponding private key',
...

Note: To build and test the entire scytl-cryptolib project, change to the directory scytl-cryptolib and do the following:

mvn clean install

How to generate the JSDoc for this module

To generate the JSDoc for this module, change to the directory scytl-cryptolib/cryptolib-js-digitalenvelope, build the module (if not already done) and do the following:

node_modules/.bin/jsdoc lib

This will generate a file called out. Double click on the file out/index.html to view the JSDoc.

How to npm install this module

To npm install this module in standalone mode, do the following:

npm install --registry https://nexus.scytl.net/content/groups/public-npm/ scytl-digitalenvelope

To npm install this module as a dependency of your own module, do the following:

1. Add the following lines to the dependencies section of your module's package.json file.

   "scytl-bitwise": "^2.1.0",
   "scytl-codec": "^2.1.0",
   "scytl-cryptopolicy": "^2.1.0",
   "scytl-symmetric": "^2.1.0",
   "scytl-asymmetric": "^2.1.0",
   "scytl-digitalenvelope": "^2.1.0",
   

2. Make sure that the .npmrc file of your module contains the following line.

   registry=https://nexus.scytl.net/content/groups/public-npm/
   

3. Install all dependencies.

   npm install
   

   How to instantiate a digital envelope service

The following example shows the default way to create a new instance of a digital envelope service.

var digitalEnvelope = require('scytl-digitalenvelope');

var envelopeService = digitalEnvelope.newService();

The following example shows how to override the default cryptographic policy used for digital envelope operations by changing the MAC hash algorithm to SHA512/224.

var cryptoPolicy = require('scytl-cryptopolicy');
var digitalEnvelope = require('scytl-digitalenvelope');

var myPolicy = cryptoPolicy.newInstance();

myPolicy.digitalEnvelope.symmetric.mac.hashAlgorithm =
  cryptoPolicy.options.digitalEnvelope.symmetric.mac.hashAlgorithm.SHA512_224;

var envelopeService = digitalEnvelope.newService({policy: myPolicy});

Note: It is desirable to use the property CryptographicPolicy.options to override the default policy, as shown above, in order to ensure that one is using an option that is allowed by the cryptographic policy.

The following example shows how to supply one's own symmetric cryptography service to the digital envelope service.

var digitalEnvelope = require('scytl-digitalenvelope');
var symmetric = require('scytl-symmetric');

var mySymmetricService = symmetric.newService({policy: myPolicy});
var envelopeService = digitalEnvelope.newService({
  policy: myPolicy,
  symmetricCrytographyService: mySymmetricService
});

Note If both a service and the cryptographic policy are specified as options, one must ensure that the specified service uses the specified policy, as shown above.

How to generate a digital envelope

The following example shows how to generate a digital envelope from a single public key (PEM encoded), given the data to store in the envelope. The data can be in the form of a byte array, wrapped in a Uint8Array object, or a string.

var envelopeGenerator = envelopeService.newGenerator(publicKeyPem);
...
var envelope = envelopeGenerator.generate(data);

The resulting digital envelope can be opened by using the private key corresponding to the public key used to generate the envelope (see next section).

The following example shows how to generate a digital envelope from multiple public keys (each PEM encoded), given the data to store in the envelope.

var envelopeGenerator = envelopeService.newGenerator(publicKey1Pem, publicKey2Pem, ...);
...
var envelope = envelopeGenerator.generate(data);

The resulting digital envelope can be opened by using any private key corresponding to one of the public keys used to generate the envelope (see next section).

How to open a digital envelope

The following example shows how to open a digital envelope and retrieve its data, using any private key corresponding to a public key that was used to generate the envelope. The output data will be in form of a byte array, wrapped in a Uint8Array object.

var envelopeOpener = envelopeService.newOpener(privateKeyPem);
...
var data = envelopeOpener.open(envelope);

Description of the digital envelope structure

The digital envelope is encapsulated by a DigitalEnvelope object, which defines the following properties and functions.

@property encryptedData The symmetrically encrypted data.
@property mac The MAC of the symmetrically encrypted data.
@property encryptedSecretKeyPairs The asymmetric encryptions of the concatenation of the encryption secret key and MAC secret key used to generate and open the digital envelope, each asymmetric encryption having been generated using a different one of the public keys used to initialize digital envelope generator.

@function toJson Serializes the object into a JSON string representation.

How to instantiate a digital envelope object.

The following example shows how to create a new DigitalEnvelope object from another envelope's properties.

var envelope = envelopeGenerator.init(publicKeyPem).generate(data);
...
var newEnvelope = envelopeService.newEnvelope(envelope.encryptedData, envelope.mac, envelope.encryptedSecretKeyPairs);

The following example shows how to serialize a DigitalEnvelope object to its corresponding JSON string representation and deserialize it by providing it as input when creating a new DigitalEnvelope object.

var envelopeJson = envelope.toJson();
...
var envelopeFromJson = envelopeService.newEnvelope(envelopeJson);