post-e-voting/source-code/scytl-cryptolib/cryptolib-js-symmetric

Symmetric Cryptography Module

This module defines the symmetric cryptography API for Scytl's JavaScript cryptographic library. The starting point for using this module is the instantiation of a symmetric cryptography 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-symmetric/lib.

To build this module, change to the directory scytl-cryptolib/cryptolib-js-symmetric 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-symmetric/spec. To run the tests, change to the directory scytl-cryptolib/cryptolib-js-symmetric 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 secret key generator 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 secret key for encryption', function()
...

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-symmetric, 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-symmetric

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-securerandom": "^2.1.0",
   "scytl-symmetric": "^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 symmetric cryptography service

The following example shows the default way to create a new instance of a symmetric cryptography service.

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

var symmetricService = symmetric.newService();

The following example shows how to override the default cryptographic policy used for symmetric cryptography operations by changing the encryption secret key length to 32 bytes.

var cryptoPolicy = require('scytl-cryptopolicy');
var symmetric = require('scytl-symmetric');

var myPolicy = cryptoPolicy.newInstance();

myPolicy.symmetric.secretKey.encryption.lengthBytes =
  cryptoPolicy.options.symmetric.secretKey.encryption.lengthBytes.KL_32;

var symmetricService = symmetric.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 secure random service object to the symmetric cryptography service.

var symmetric = require('scytl-symmetric');
var secureRandom = require('scytl-securerandom');

var mySecureRandomService = secureRandom.newService();

var symmetricService = symmetric.newService({secureRandomService: mySecureRandomService});

How to generate secret keys

The following examples show how to generate a secret key for encryption and a secret key for MAC generation. The keys will be returned in the form of a byte array, wrapped in a Uint8Array object.

var keyGenerator = symmetricService.newKeyGenerator();

var encryptionKey = keyGenerator.nextEncryptionKey());
var macKey = keyGenerator.nextMacKey());

How to encrypt and decrypt data

The following examples show how to symmetrically encrypt and decrypt some data. The data to encrypt can be in the form of a string or a byte array, wrapped in a Uint8Array object. The output of both the encrypt and decrypt operations will be a byte array, wrapped in a Uint8Array object. To retrieve encrypted data of type string, the result of the decryption must be UTF-8 decoded.

var codec = require('scytl-codec');
...
var cipher = symmetricService.newCipher().init(encryptionKey);

var encryptedData = cipher.encrypt('myData');
var decryptedData = codec.utf8Decode(cipher.decrypt(encryptedData));
expect(decryptedData).toBe('myData');

var encryptedData = cipher.encrypt(new Uint8Array[0x01, 0x02, 0x03]);
var decryptedData = cipher.decrypt(encryptedData);
expect(decryptedData).toEqual(new Uint8Array[0x01, 0x02, 0x03]);

How to generate and verify a MAC

The following examples show how to generate and verify a MAC from some data. The data for MAC generation or verification can be in the form of a string or a byte array, wrapped in a Uint8Array object. The output of the MAC generation will be in the form of a byte array, wrapped in a Uint8Array object.

var macHandler = symmetricService.newMacHandler().init(macKey);
...

var mac = macHandler.generate('myData');
var verified = macHandler.verify(mac, 'myData');
expect(verified).toBeTruthy();

var mac = macHandler.generate(new Uint8Array[0x01, 0x02, 0x03]);
var verified = macHandler.verify(mac, new Uint8Array[0x01, 0x02, 0x03]);
expect(verified).toBeTruthy();

The following example shows how to generate a MAC from multiple data parts.

var dataParts = ['myData1', 'myData2', 'myData3'];
...

for (var i = 0; i < dataParts.length; i++) {
  macHandler.update(dataParts[i]);
}
var mac = macHandler.generate();

--or--

for (var i = 0; i < (dataParts.length-1); i++) {
  macHandler.update(dataParts[i]);
}
var mac = macHandler.generate('myData3');

The following example shows how to verify a MAC from multiple data parts.

for (var j = 0; j < dataParts.length; j++) {
  macHandler.update(dataParts[j]);
}
var verified = macHandler.verify(mac);

--or--

for (var j = 0; j < (dataParts.length-1); j++) {
  macHandler.update(dataParts[j]);
}
var verified = macHandler.verify(mac, 'myData3');

The following example shows how to generate a MAC from multiple data parts, using method chaining.

var mac = macHandler.update('myData1').update('myData2').update('myData3').generate();

--or--

var mac = macHandler.update('myData1').update('myData2').generate('myData3');

The following example shows how to verify a MAC from multiple data parts, using method chaining.

var verified = macHandler.update('myData1').update('myData2').update('myData3').verify(mac);

--or--

var verified = macHandler.update('myData1').update('myData2').verify(mac, 'myData3');