{"id":160824,"date":"2016-04-07T18:37:44","date_gmt":"2016-04-07T16:37:44","guid":{"rendered":"http:\/\/mybroadband.co.za\/news\/?p=160824"},"modified":"2016-04-07T18:38:57","modified_gmt":"2016-04-07T16:38:57","slug":"how-whatsapp-keeps-your-messages-secret","status":"publish","type":"post","link":"https:\/\/mybroadband.co.za\/news\/security\/160824-how-whatsapp-keeps-your-messages-secret.html","title":{"rendered":"How WhatsApp keeps your messages secret"},"content":{"rendered":"

WhatsApp has extended the Signal Protocol<\/strong><\/a> it uses to provide end-to-end encryption to all\u00a0platforms.<\/p>\n

Open Whisper Systems\u00a0said<\/a><\/strong>\u00a0it has integrated its Signal Protocol into WhatsApp\u2019s Android, iPhone, Windows Phone, Nokia S40, Nokia S60, BlackBerry, and BlackBerry 10 apps.<\/p>\n

Signal Protocol is an open-source, forward-secure, encryption protocol for asynchronous messaging systems.<\/p>\n

WhatsApp released a white paper<\/a><\/strong>\u00a0which gives a technical overview of how its encryption system works – as detailed below.<\/p>\n

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How encryption works<\/h3>\n

Encryption systems are\u00a0typically based on a combination of public-key and symmetric-key cryptography.<\/p>\n

In public-key cryptography, you and the person you want to chat to generate two “keys”: a\u00a0public one that anyone can see, and a private one that you have to keep secret.<\/p>\n

You use\u00a0someone’s public key to encrypt a message only they can see, which they decrypt with their secret private key. This is illustrated below.<\/p>\n

\"Public-key<\/a>

Public-key encryption from MakeUseOf<\/a><\/p><\/div>\n

For a messaging system like WhatsApp, private keys are typically used to exchange symmetric keys – which must be securely generated.<\/p>\n

Messages are then encrypted with the shared symmetric keys, which all\u00a0parties in a conversation\u00a0share.<\/p>\n

\"Symmetric-key<\/a>

Symmetric-key encryption by MakeUseOf<\/a><\/p><\/div>\n

The Signal Protocol implemented in\u00a0WhatsApp is more complex than the example above, with more keys used to generate other keys<\/a>.<\/strong><\/p>\n

For example, the same symmetric key is not used to encrypt all messages in a conversation, but WhatsApp avoids the expensive operation of exchanging the new key with\u00a0a public-key encrypted message.<\/p>\n

Although there are differences between the example above and the Signal Protocol,\u00a0the principle remains\u00a0the same.<\/p>\n

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Registration<\/h3>\n

When you register, WhatsApp sends a public Identity Key, public Signed Pre Key with its signature, and a batch of public One-Time Pre Keys to the server.<\/p>\n

WhatsApp\u2019s servers never access your private keys.<\/p>\n

\"WhatsApp<\/a>

WhatsApp initialisation<\/p><\/div>\n

\n

Setting up an encrypted chat or call<\/h3>\n

Your WhatsApp\u00a0clients first need to establish an encrypted session.<\/p>\n

Once the session is established, clients do not need to set up a new session with each other unless something causes the session state to be lost.<\/p>\n

This can happen if you reinstall the app, or switch to a different device.<\/p>\n

Until everyone on WhatsApp has updated to the latest version of the app, some chats may still be unencrypted.<\/p>\n

WhatsApp displays notifications in chats that are secure. You can also verify that a chat is secure via the chat’s menu.<\/p>\n

\"WhatsApp<\/a>

WhatsApp Signal Protocol encryption verification<\/p><\/div>\n

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Receiving Session Setup<\/h3>\n

After building the encryption session, the person who started the chat can start sending messages.<\/p>\n

Until the recipient responds, the initiator includes the information needed for the recipient to build a corresponding session in the header of all messages sent.<\/p>\n

Once a session has been established, clients exchange messages that are protected with a Message Key using AES256 in CBC mode for encryption and HMAC-SHA256 for authentication.<\/p>\n

Large attachments – video, audio, images, or files – are also encrypted.<\/p>\n

\n

Group Messages<\/h3>\n

WhatsApp uses similar\u00a0mechanisms to encrypt group messages.<\/p>\n

One difference is that the sending WhatsApp client generates a Sender Key, which is encrypted and transmitted to each of the group\u2019s members individually.<\/p>\n

Whenever a group member leaves, all group participants clear their Sender Key and start over.<\/p>\n

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Verifying Keys<\/h3>\n

WhatsApp gives users the option to verify the keys of other users.<\/p>\n

This lets you confirm that neither an unauthorised third party nor WhatsApp have initiated a man-in-the-middle attack.<\/p>\n

This can be done by scanning a QR code, or by comparing a 60-digit number, as depicted below.<\/p>\n

\"WhatsApp<\/a>

WhatsApp Signal Protocol key verification<\/p><\/div>\n

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Transport Security<\/h3>\n

All communication between WhatsApp clients and servers is layered within a separate encrypted channel.<\/p>\n

On Windows Phone, iPhone, and Android, end-to-end encryption uses noise pipes with Curve25519, AES-GCM, and SHA256 from the Noise Protocol Framework for long-running interactive connections.<\/p>\n

WhatsApp said this provides clients with:<\/p>\n

    \n
  1. Extremely fast, lightweight connection setup and resume.<\/li>\n
  2. Metadata is encrypted, hiding it from unauthorised network observers. No information about the connecting user\u2019s identity is revealed.<\/li>\n
  3. No client authentication secrets are stored on the server. If the server\u2019s user database is compromised, no private authentication credentials will be revealed.<\/li>\n<\/ol>\n
    \n

    Summary of key types<\/h3>\n

    Public Key Types<\/strong><\/p>\n