Realtime Client Library API

Encryption

Ably client libraries support built-in symmetric encryption of message content, making it easier to build apps that encrypt content fully end-to-end. Whilst TLS is enabled by default and ensures that data is securely sent to and received from Ably, messages are not encrypted within the Ably system. Using the encryption feature of our client libraries ensures that message payloads are opaque, can never be decrypted by Ably, and can only be decrypted by other clients that share your secret key.

Getting started

Channels can be easily configured to automatically encrypt and decrypt all message payloads using the secret key provided in the channel options. Below is a simple example:

Ably.Realtime.Crypto.generateRandomKey(function(err, key) {
  var channelOpts = { cipher: { key: key } };
  var channel = realtime.channels.get('beg-gem-end', channelOpts);
  channel.subscribe(function(message) {
    alert('Decrypted data: ' + message.data);
  });
  channel.publish('unencrypted', 'encrypted secret payload');
});
Ably.Realtime.Crypto.generateRandomKey(function(err, key) {
  var channelOpts = { cipher: { key: key } };
  var channel = realtime.channels.get('beg-gem-end', channelOpts);
  channel.subscribe(function(message) {
    alert('Decrypted data: ' + message.data);
  });
  channel.publish('unencrypted', 'encrypted secret payload');
});
key = Ably::Util::Crypto.generateRandomKey()
channel_opts = { cipher: { key: key } }
channel = realtime.channels.get('beg-gem-end', channel_opts)
channel.subscribe do |message|
  puts "Decrypted data: #{message.data}"
end
channel.publish 'unencrypted', 'encrypted secret payload'
ChannelOptions options = ChannelOptions.withCipherKey(<key>);
Channel channel = realtime.channels.get("beg-gem-end", options);
channel.subscribe(new MessageListener() {
  @Override
  public void onMessage(Message message) {
    System.out.println("Decrypted data: " + message.data);
  }
});
channel.publish('unencrypted', 'encrypted secret payload');
var key = Crypto.GenerateRandomKey();
var options = new ChannelOptions(key);
var channel = realtime.Channels.Get("beg-gem-end", options);
channel.Subscribe(message => {
  Console.WriteLine("Decrypted data: " + message.data);
});
channel.Publish("unencrypted", "encrypted secret payload");
ARTChannelOptions *options = [[ARTChannelOptions alloc] initWithCipherKey:<key>];
ARTRealtimeChannel *channel = [realtime.channels get:@"beg-gem-end" options:options];
[channel subscribe:^(ARTMessage *message) {
  NSLog(@"Decrypted data: %@", message.data);
}];
[channel publish:@"unencrypted" data:@"encrypted secret payload"];
let options = ARTChannelOptions(cipherKey: <key>)
let channel = realtime.channels.get("beg-gem-end", options: options)
channel.subscribe { message in
  print("Decrypted data: \(message.data)")
}
channel.publish("unencrypted", data: "encrypted secret payload")

Note that all examples on this page assume you are running them within an EventMachine reactor. Find out more in our Realtime usage documentation.

Note that the key should not be a pass-phrase, but a cryptographic key – generated from a secure random source, 128 or 256 bits long, binary or base64-encoded. If you wish to encrypt messages with a pass-phrase (for example, one entered by a user), you should use a key derivation function to transform that into a key. The client libraries are also capable of generating a random key for you.

Understanding encryption

The libraries support encryption purely as a convenience; the libraries ensure interoperability between environments by having compatible implementations of encryption algorithms and by making common choices on format, mode, padding etc. However, Ably intentionally does not manage the distribution of keys between clients, and end-to-end encryption is enabled without exposing keys to the Ably service at all. This has the advantage that Ably demonstrably has no access to the un-encrypted contents of your messages, but also means that each app is responsible for enabling the distribution of keys to clients independently of Ably.

The client library support for encryption supports symmetric encryption only, and requires each participating client to each specify the correct CipherParams secret key when creating a Channel instance. Clients that do not specify a key will be delivered the still-encrypted message payloads that they may then still wish to decrypt offline.

The client libraries are designed to be extensible, but initially only support the AES algorithm (with a default key length of 256 bits) and CBC mode. These defaults are intended to ensure that encryption support can be provided in all target environments and platforms.

Encryption is supported for the data attribute (payload) of published messages and presence member messages on a channel, over both REST and Realtime publish operations. Decryption is supported in Realtime message and presence message subscriptions and in REST and Realtime history operations.

All other attributes of messages and presence messages, such as event name or clientIdclient_idClientId remain un-encrypted. All sensitive data, when using the library’s symmetric encryption, must be placed in the data attribute to ensure it is encrypted before it is transmitted to Ably.

The key in use at any given time is known by the client library, but the Ably service has no visibility of the key; it knows only that a given message payload was encrypted. When accessing messages via the history API, it is the caller’s responsibility to ensure that the correct key is configured for the channel before the history request is made.

Encryption options (algorithm, key, etc) are specified on a per-channel basis; it is expected that apps may wish to have both un-encrypted and encrypted channels on a single connection.

Crypto API Reference

The Ably.Realtime.Ably::Util::io.ably.lib.util.ARTCrypto object exposes the following public methods:

Methods

getDefaultParamsget_default_paramsGetDefaultParams

CipherParams Crypto.getDefaultParams(Object params)CipherParams Crypto.get_default_params(Hash params)CipherParams Crypto.getDefaultParams(Param[] params)getDefaultParams(values: [NSObject : AnyObject]) → ARTCipherParamsstatic CipherParams GetDefaultParams(byte[] key = null, byte[] iv = null, CipherMode? mode = null)

This call obtains a CipherParams object using the values passed in (which must be a subset of CipherParams fields that at a minimum includes a key), filling in any unspecified fields with default values, and checks that the result is a valid and self-consistent.

You will rarely need to call this yourself, since the client library will handle it for you if you specify cipher params when initializing a channel (as in the example at the top) or when setting channel options with channel.setOptions().

Parameters

paramsarguments
The cipher paramsarguments that you want to specify. It must at a minimum include a key, which should be either a binary (byte[]ArrayBuffer or WordArrayBufferbyte arrayNSData) or a base64-encoded NSString.

Returns

On success, the method returns a complete CipherParams object. Failure will raise an AblyException exception.

Example

var cipherParams = Ably.Realtime.Crypto.getDefaultParams({key: <key>});
var channelOpts = { cipher: cipherParams };
var channel = realtime.channels.get('beg-gem-end', channelOpts);
var cipherParams = Ably.Realtime.Crypto.getDefaultParams({key: <key>});
var channelOpts = { cipher: cipherParams };
var channel = realtime.channels.get('beg-gem-end', channelOpts);
cipher_params = Ably::Util::Crypto.get_default_params({key: <key>})
channel_opts = { cipher: cipher_params }
channel = realtime.channels.get('beg-gem-end', channel_opts)
CipherParams params = Crypto.getDefaultParams(new Param[]{ new Param("key", <key>) });
ChannelOptions options = new ChannelOptions();
options.encrypted = true;
options.cipherParams = params;
Channel channel = realtime.channels.get("beg-gem-end", options);
var @params = Crypto.GetDefaultParams(<key>);
ChannelOptions options = new ChannelOptions(@params);
var realtime = new AblyRealtime("xVLyHw.NwPSIw:JvRopf8rLZGFtbYs");
var channel = realtime.Channels.Get("beg-gem-end", options);
ARTCipherParams *params = [ARTCrypto getDefaultParams:@{@"key": <key>}];
ARTChannelOptions *options = [[ARTChannelOptions alloc] initWithCipher:params];
ARTRealtimeChannel *channel = [realtime.channels get:@"beg-gem-end" options:options];
let params = ARTCrypto.getDefaultParams(["key": <key>])
let options = ARTChannelOptions(cipher: params)
let channel = realtime.channels.get("beg-gem-end", options: options)
generateRandomKeygenerate_random_keyGenerateRandomKey

Crypto.generateRandomKey(Int keyLength?, callback(ErrorInfo err, Buffer key))byte array Crypto.generate_random_key(Int key_length?)byte[] Crypto.generateRandomKey(Int keyLength?)generateRandomKey(length?: UInt) → NSDatastatic byte[] GenerateRandomKey(CipherMode? mode = null, int? keyLength = null)

This call obtains a randomly-generated binary key of the specified key length.

Parameters

keyLengthkey_length
Optional Int with the length of key to generate. For AES, this should be either 128 or 256. If unspecified, defaults to 256128.
mode
Optional AES CipherMode which is used when the key is generated
callback
is a function of the form function(err, key) which is called upon completion

Callback result

On successfully generating a key, the callback is called with that key as a WordArrayBuffer, and err is null. On failure to create a key, err contains an ErrorInfo object describing the failure reason.

Returns

On success, the method returns the generated key as a byte[] arraybyte arrayNSData. Failure will raise an AblyException .

Example

Ably.Realtime.Crypto.generateRandomKey(256, function(err, key) {
  if(err) {
    console.log("Key generation failed: " + err.toString());
  } else {
    var channel = realtime.channels.get('beg-gem-end', {cipher: {key: key}});
  }
});
Ably.Realtime.Crypto.generateRandomKey(256, function(err, key) {
  if(err) {
    console.log("Key generation failed: " + err.toString());
  } else {
    var channel = realtime.channels.get('beg-gem-end', {cipher: {key: key}});
  }
});
key = Ably::Util::Crypto.generate_random_key(256)
channel = realtime.channels.get('beg-gem-end', {cipher: {key: key}})
byte[] key = Crypto.generateRandomKey(256);
ChannelOptions options = ChannelOptions.withCipher(key);
Channel channel = realtime.channels.get("beg-gem-end", options);
byte[] key = Crypto.GenerateRandomKey(keyLength: 256);
var options = new ChannelOptions(key);
var channel = realtime.Channels.Get("beg-gem-end", options);
NSData *key = [ARTCrypto generateRandomKey:256];
ARTChannelOptions *options = [[ARTChannelOptions alloc] initWithCipherKey:key];
ARTRealtimeChannel *channel = [realtime.channels get:@"beg-gem-end" options:options];
let key = ARTCrypto.generateRandomKey(256)
let options = ARTChannelOptions(cipherWithKey: key)
let channel = realtime.channels.get("beg-gem-end", options: options)

ChannelOptions ObjectARTChannelOptionsChannelOptions Hashio.ably.types.ClientOptionsIO.Ably.ClientOptions

Currently the supported channel options are only used for configuring encryption.

ChannelOptions, a plain Javascript object, may optionally be specified when instancing a Channel, and this may be used to specify channel-specific options. The following attributes can be defined on the object:

ChannelOptions, a Hash object, may optionally be specified when instancing a Channel, and this may be used to specify channel-specific options. The following key symbol values can be added to the Hash:

ChannelOptions, an Associative Array, may optionally be specified when instancing a Channel, and this may be used to specify channel-specific options. The following named keys and values can be added to the Associated Array:

ARTio.ably.lib.types.ChannelOptions may optionally be specified when instancing a Channel, and this may be used to specify channel-specific options.

IO.Ably.ChannelOptions may optionally be specified when instancing a Channel, and this may be used to specify channel-specific options.

PropertiesMembersAttributes

cipher:cipherCipherParams
Requests encryption for this channel when not null, and specifies encryption-related parameters (such as algorithm, chaining mode, key length and key). See an example
Type: CipherParams or an options objecta Param[] listan options hashan Associative Array containing at a minimum a key

Static methods

withCipherKey

static ChannelOptions.withCipherKey(Byte[] or String key)

A helper method to generate a ChannelOptions for the simple case where you only specify a key.

Parameters

key
A binary Byte[] array or a base64-encoded String.

Returns

On success, the method returns a complete ChannelOptions object. Failure will raise an AblyException.

CipherParamsARTCipherParamsCipherParams Hashio.ably.lib.util.Crypto.CipherParamsIO.Ably.CipherParams

A CipherParams contains configuration options for a channel cipher, including algorithm, mode, key length and key. Ably client libraries currently support AES with CBC, PKCS#7 with a default key length of 256 bits. All implementations also support AES128.

Individual client libraries may support either instancing a CipherParams directly, using Crypto.getDefaultParams()Crypto.GetDefaultParams()Crypto.get_default_params(), or generating one automatically when initializing a channel, as in this example.

PropertiesMembersAttributes

keyKey:key
A binary (byte[]ArrayBuffer or WordArrayBufferbyte arrayNSData) containing the secret key used for encryption and decryption
algorithm:algorithmAlgorithm
AES The name of the algorithm in the default system provider, or the lower-cased version of it; eg “aes” or “AES
Type: String
key_length:key_lengthkeyLengthKeyLength
256_128 The key length in bits of the cipher, either 128 or 256
Type: Integer_
mode:modeMode
CBC The cipher mode
Type: StringCipherMode
keySpec
A KeySpec for the cipher key
Type: SecretKeySpec

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