Home Cyber Attack Raccoon Attack Aims At Breaking TLS Encryption – Though Attack Is ‘Rare’

Raccoon Attack Aims At Breaking TLS Encryption – Though Attack Is ‘Rare’

by Abeerah Hashim
Raccoon attack

Researchers have found a way to break TLS encryption, dubbed the Raccoon attack, however it has numerous limitations that make real-time exploitation difficult.

About Raccoon Attack On TLS

A team of researchers has devised a new attack strategy breaking TLS encryption. Dubbed Raccoon (because they feel that this cute animal deserves that an attack is named after them), this side-channel attack targets the TLS cryptographic protocol, which subsequently allows decrypting the HTTPS connection. Also, it aims at all other services that use TLS and SSL.

Specifically, it’s a timing attack that targets the Diffie-Hellman (DH) key exchange process of TLS.

The researchers explain that all TLS versions up to 1.2 require stripping of the leading zero bytes from the DH premaster secret before further use for deriving connection secrets. The Key Derivation Function (KDF) then applies hash function to the input premaster secret, which, with leading zeros stripped, uses fewer iterations. Otherwise, it is slower and requires more hash blocks.

In simple words, they stated,

Processing an additional hash block results in an additional hash compression computation. Therefore, for some DH modulus sizes, the KDF is faster for premaster secrets with leading zero bytes, since these zero bytes will be stripped.

This is what the Raccoon attack exploits.

If an attacker can learn the number of hash compression computations performed with the premaster secret based on precise timing measurements, the attacker is also able to learn some leading bits of the premaster secret. This behavior allows the attacker to create a most significant bits (MSB) oracle from a server and to determine the most significant bits of the DH secret.

Defining the Raccoon attack, they state,

The Raccoon attack can recover TLSDH(E) premaster secrets from passively-observed TLSDH(E) sessions by exploiting a side channel in the server and solving the Hidden Number Problem using lattice reduction algorithms.

They have presented the details of their findings in a research paper, alongside setting up a dedicated website for this attack.

Exploit Probability Very Low

The Raccoon attack, if ever exploited, can lead to dangerous consequences. The potential decrypting of the secure connection between the user and the server can allow exposure of sensitive information such as login credentials, credit card numbers, IMs, and more.

However, fortunately, a real-world exploit of this attack is quite rare due to several limitations. As the researchers explain,

The attacker needs particular circumstances for the Raccoon attack to work. He needs to be close to the target server to perform high precision timing measurements. He needs the victim connection to use DH(E) and the server to reuse ephemeral keys. And finally, the attacker needs to observe the original connection. For a real attacker, this is a lot to ask for.

Also, this is typically a server-side attack and requires separate attempts on individual target connections.

Besides, the TLS 1.3 remains unaffected by this attack as it preserves the leading zero bytes for DHE cipher suites. Though, a TLS 1.3 variant is exploitable as it allows key reuse. Hence, the researchers do not recommend that variant.

Before the disclosure, the researchers have responsibly disclosed the matter to different vendors. Hence, this flaw, that existed for the past 20 years, has received CVE IDs and patches. The CVE numbers are: CVE-2020-5929 (F5), CVE-2020-1968 (OpenSSL), CVE-2020-12413 (Mozilla), and CVE-2020-1596 (Microsoft).

You may also like

Latest Hacking News

Privacy Preference Center


The __cfduid cookie is used to identify individual clients behind a shared IP address and apply security settings on a per-client basis.

cookie_notice_accepted and gdpr[allowed_cookies] are used to identify the choices made from the user regarding cookie consent.

For example, if a visitor is in a coffee shop where there may be several infected machines, but the specific visitor's machine is trusted (for example, because they completed a challenge within your Challenge Passage period), the cookie allows Cloudflare to identify that client and not challenge them again. It does not correspond to any user ID in your web application, and does not store any personally identifiable information.

__cfduid, cookie_notice_accepted, gdpr[allowed_cookies]


DoubleClick by Google refers to the DoubleClick Digital Marketing platform which is a separate division within Google. This is Google’s most advanced advertising tools set, which includes five interconnected platform components.

DoubleClick Campaign Manager: the ad-serving platform, called an Ad Server, that delivers ads to your customers and measures all online advertising, even across screens and channels.

DoubleClick Bid Manager – the programmatic bidding platform for bidding on high-quality ad inventory from more than 47 ad marketplaces including Google Display Network.

DoubleClick Ad Exchange: the world’s largest ad marketplace for purchasing display, video, mobile, Search and even Facebook inventory.

DoubleClick Search: is more powerful than AdWords and used for purchasing search ads across Google, Yahoo, and Bing.

DoubleClick Creative Solutions: for designing, delivering and measuring rich media (video) ads, interactive and expandable ads.



The _ga is asssociated with Google Universal Analytics - which is a significant update to Google's more commonly used analytics service. This cookie is used to distinguish unique users by assigning a randomly generated number as a client identifier. It is included in each page request in a site and used to calculate visitor, session and campaign data for the sites analytics reports. By default it is set to expire after 2 years, although this is customisable by website owners.

The _gat global object is used to create and retrieve tracker objects, from which all other methods are invoked. Therefore the methods in this list should be run only off a tracker object created using the _gat global variable. All other methods should be called using the _gaq global object for asynchronous tracking.

_gid works as a user navigates between web pages, they can use the gtag.js tagging library to record information about the page the user has seen (for example, the page's URL) in Google Analytics. The gtag.js tagging library uses HTTP Cookies to "remember" the user's previous interactions with the web pages.

_ga, _gat, _gid