Crypto

This document describes the Crypto library available in the JavaScript environment for app serivices.

Table of content

Object	Crypto
Functions	hash hmac cipher ecdh
Object	Hash
Functions	update final
Object	Hmac
Functions	update final
Object	Cipher
Members	iv getIv crypt close
Object	Ecdh
Members	public secret close
Examples	Encrypting and signing a JS object

Crypto

hash

Creates a Hash object that can be used for the calculation of cryptographic hashes.

The objects allocates persistent memory in the JavaScript Runtime until the final function is called.

Parameters

string algorithm

The hash algorithm to be used. Supported values are "SHA224", "SHA256", "SHA384", "SHA512", "SHA512_224", "SHA512_256", "SHA1", "MD5", "MD4".

Return value

Hash	An object that can be used for the hash calculation.

var digest = Crypto.hash("SHA256").update("data1").update("data2").final();

hmac

Creates a Hmac object that can be used for the calculation of a hash-based message authentication code.

The objects allocates persistent memory in the JavaScript Runtime until the final function is called.

Parameters

string algorithm	The hash algorithm to be used. Supported values are "SHA224", "SHA256", "SHA384", "SHA512", "SHA512_224", "SHA512_256", "SHA1", "MD5", "MD4".
string/Uint8Array key	The password or key that shall be used for the calculation.

Return value

Hmac	An object that can be used for the HMAC calculation.

var mac = Crypto.hmac("SHA256","password").update("data1").update("data2").final();

cipher

Creates a Cipher object that can be used for the encryption / decryption.

The objects allocates persistent memory in the JavaScript Runtime until close or crypt with last=true is called.

Note: Cryptography is non-trivial. It's easy to make small mistakes on application level that break security completely. Don't just use the library functions but make sure you have a good understanding how to use the specific algorithm and mode.

Parameters

string algorithm	The cryptographic algorithm to be used. Supported values are "AES", "RC4", "DES".
string mode	The mode of operation to be used. Supported modes for "AES" are "ECB", "CTR", "CBC", "CTS", "CFB". null defaults to "ECB". Supported modes for "DES" are "CBC". Use null for "RC4".
string/Uint8Array key	The key for encryption/decryption. For "AES" a key of 16 bytes (AES-128), 24 bytes (AES-192) or 32 bytes (AES-256) is needed. The function accepts both hexstrings and binary keys given as a Uint8Array. For "DES" a key of 8 bytes (64 bit) is needed. The function accepts both hexstrings and binary keys given as a Uint8Array. For "RC4" a key of arbitrary length can be used. It can be specified as a string (password) or as a binary key given as a Uint8Array. Important: Never reuse the same key for "RC4". As RC4 is a stream cipher, the key needs to be globally unique to maintain security. Important: Never reuse the same key/iv combination for "AES" in "CTR" mode. As AES-CTR is a stream cipher, the key/iv combination needs to be globally unique to maintain security.
bool encrypt	true for encryption (default). false for decryption Note: For stream ciphers like RC4 or AES-CTR there is no difference between encryption and decryption, so both values give the same result.

Return value

cipher

An object that can be used for performing the encryption or decryption.

var ciphertext = Crypto.cipher("RC4", null, "password").crypt("secretdata");
var decrypted = Crypto.cipher("RC4", null, "password").crypt(ciphertext);

ecdh

Creates an Ecdh object that can be used for Diffie-Hellman key agreement using elliptic curves.

The supported curve is Secp256r1 also known as P-256.

The objects allocates persistent memory in the JavaScript Runtime until close or secret is called.

Return value

Ecdh	An object that can be used for performing the ECDH key agreement.

var ecdh = Crypto.ecdh();
var localPublicKey = ecdh.public();
var remotePublicKey = "aec36e41791fabfc2ddd3223a8ef59a658a9e30cd92a5d241bbf4c18684a4a61c9aa0d1d9d3181d3022d2f64c7663000915622d4e670cce86737bb00cab5de91";
var sharedSecret = ecdh.secret(remotePublicKey);

Hash

update

Includes a chunk of data into the hash calculation.

Parameters

string/Uint8Array key

The input data. The function accepts both strings and binary data as Uint8Array.

Return value

Hash	A reference to the object itself. Useful for method chaining.

final

Caluclates the hash value.

Parameters

bool binary

Optional, defaulting to false. Specifies if the function should return the hash value as a hexstring or as a binary Uint8Array.

Return value

string/Uint8Array

The calculated hash value as a hexstring or Uint8Array, depending on the binary parameter.

Remarks

Calling this function will delete the object and free all associated memory in the JavaScript Runtime.

var digestHexString = Crypto.hash("SHA256").update("data1").update("data2").final();
var digestBinary = Crypto.hash("SHA256").update("data1").update("data2").final(true);

Hmac

update

Includes a chunk of data into the HMAC calculation.

Parameters

string/Uint8Array key

The input data. The function accepts both strings and binary data as Uint8Array.

Return value

Hmac	A reference to the object itself. Useful for method chaining.

final

Caluclates the HMAC value.

Parameters

bool binary

Optional, defaulting to false. Specifies if the function should return the hash value as a hexstring or as a binary Uint8Array.

Return value

string/Uint8Array

The calculated hash value as a hexstring or Uint8Array, depending on the binary parameter.

Remarks

Calling this function will delete the object and free all associated memory in the JavaScript Runtime.

var hacHexString = Crypto.hmac("SHA256","password").update("data1").update("data2").final();
var hmacBinary = Crypto.hmac("SHA256","password").update("data1").update("data2").final(true);

Cipher

Sets an explicit initialization vector. If the function is never called, an IV consisting of null bytes is used.
The following modes of operation use an initialization vector: "CTR", "CFB", "CBC", "CTS".
"AES" uses an initialization vector of 16 bytes
"DES" uses an initialization vecrot of 8 bytes

Parameters

string/Uint8Array iv

The initialzation vector to be used from the next crypt operation. The function accepts both hexstrings and binary data as Uint8Array.

Return value

cipher

A reference to the object itself. Useful for method chaining.

getIv

Returns the current IV.

Parameters

bool binary

Optional, defaulting to false. Specifies if the function should return a hexstring or a binary Uint8Array.

Return value

string/Uint8Array

The current IV value as a hexstring or Uint8Array, depending on the binary parameter.

crypt

Encrypts or decrypts a chunk of data.

Parameters

string/Uint8Array data	The data to be encrypted/decrypted. For encryption the functions accepts strings or binary data as Uint8Array. For decryption the function accepts hexstrings or binary data as Uint8Array. Depending on the algorithm and mode of operation there are restrictions on the data size that can be processed. "RC4" allows arbitrary data sizes. "AES" in "CTR" or "CTS" mode allow arbitary data sizes. All other modes of "AES" expect multiples of 16 bytes "DES" expects multiples of 8 bytes
bool binary	Optional, defaulting to false. If false, the function will return a hexstring for encryption and a string for decryption. Otherwise the function will return binary data as a Uint8Array.
bool last	Optional, defaulting to true. If true, the Cipher object will be deleted after the operation, along with all associated data in the JavaScript Runtime. if false, the object can be reused for encrypting / decrypting additional chunks of data.

Return value

string/Uint8Array

The encrypted/decrypted data a string/hexstring or Uint8Array, depending on the binary parameter.

var key = "73757065727375706572736563726574";
var iv = "00000000000000000000000000000000";
var plaintext = "This is the secret text to be encrypted";

// encryption using AES-128 in CTR mode
var ciphertext = Crypto.cipher("AES", "CTR", key, true).iv(iv).crypt(plaintext);

// decryption using AES-128 in CTR mode
var decrypted = Crypto.cipher("AES", "CTR", key, false).iv(iv).crypt(ciphertext);

// now decrypted contains the plain text again

Deletes the object and frees all associated data in the JavaScript Runtime. Can be used to dispose the object, as an alternative to calling close with last set to true.

Ecdh

public

Returns the local 64 byte public key for the ECDHE key agreement. The public key is sent to the remote party.

Parameters

bool binary

Optional, defaulting to false. Specifies if the function should return a hexstring or a binary Uint8Array.

Return value

string/Uint8Array

The local public key as a hexstring or Uint8Array, depending on the binary parameter.

secret

Calculates a 32 byte shared secret using the remote public key.

Parameters

string/Uint8Array remotePublicKey	The public key of the remote party. Must be 64 bytes of data. The functions accepts both hexstrings or binary data as Uint8Array.
bool binary	Optional, defaulting to false. If true, the function will return a Uint8Array. Otherwise the function will return a hexstring.

Return value

string/Uint8Array

The 32 byte shared secret as a hexstring or Uint8Array, depending on the binary parameter.

// This example illustrates how two parties (A and B) can calculate a shared secret.
var a = Crypto.ecdh();
var b = Crypto.ecdh();

// A and B calculate their public key and send it to each other
var publicA = a.public();
var publicB = b.public();

// A and B calculate the same shared secret using the public key of the remote party
var secretA = a.secret(publicB);
var secretB = b.secret(publicA);

log(secretA == secretB); // true

Deletes the object and frees all associated data in the JavaScript Runtime. Can be used to dispose the object, if secret was not called.

Example: Encrypting and signing a JS object

Let's make up an example that brings everything together. For that let's create a function that does the following:

Serialize an object to a JSON string.
Create a message authentication code for the string using HMAC-SHA256 and a secret passphrase.
Encrypt the string using AES-256 in CTR mode with the secret passphrase.
Construct an object that includes all information needed to decrypt again - except for the secret passphrase of course.

function encryptObject(obj, passphrase) {
    // serialize the object
    var plaintext = JSON.stringify(obj);
    // calculate HMAC
    var hmac = Crypto.hmac("SHA256", passphrase).update(plaintext).final();
    // create random 128-Bit IV
    var iv = Random.bytes(16);
    // create 256-Bit encryption key from passphrase by hashing it using SHA256
    var key = Crypto.hash("SHA256").update(passphrase).final();
    // encrypt
    var ciphertext = Crypto.cipher("AES", "CTR", key, true).iv(iv).crypt(plaintext);
    
    return {
        iv: iv,
        data: ciphertext,
        hmac: hmac
    };
}

Next, let's create the corresponding decryption function.

Read all information from the object.
Decrypt using AES-256 in CTR mode with the secret passphrase.
Verify the decrypted data using HMAC-SHA256 and the secret passphrase.
Restore the original object.

function decryptObject(obj, passphrase) {
    if (!obj || !obj.iv || !obj.data || !obj.hmac) return null;

    // create 256-Bit encryption key from passphrase by hashing it using SHA256
    var key = Crypto.hash("SHA256").update(passphrase).final();
    // decrypt
    var plaintext = Crypto.cipher("AES", "CTR", key, false).iv(obj.iv).crypt(obj.data);
    // calculate HMAC
    var hmac = Crypto.hmac("SHA256", passphrase).update(plaintext).final();

    // check if decryption was successfull
    if (hmac == obj.hmac) {
        return JSON.parse(plaintext);
    }
    
    return null;
}

We can test it with the following code.


var passphrase = "D4s 1s7 d4s H4us v0m N1c0l4us!!1";

var input = { text: "Hi, this is top secret. We should protect it.", x: 42 };
log("input:     " + JSON.stringify(input));

var encrypted = encryptObject(input, passphrase);
log("encrypted: " + JSON.stringify(encrypted));

var decrypted = decryptObject(encrypted, passphrase);
log("decrypted: " + JSON.stringify(decrypted));

In the log we can see an output like that:


JS: input:     {"text":"Hi, this is top secret. We should protect it.","x":42}
JS: encrypted: {"iv":"357bf81d63418a6fdedce56558667d29","data":"f0a454da39d7306770afc7ea781904b2d49b4adb9d4f1790898d28145503a8d2183e4c53ec4e696a95938ee1c25bf5d29b24851c45a31fc6e13842887b267c","hmac":"9502652073243900ae42a4b864b05d17c3ec18b0983e3aa9ae76099be5642bac"}
JS: decrypted: {"text":"Hi, this is top secret. We should protect it.","x":42}