F5 Friday: The 2048-bit Keys to the Kingdom

There’s a rarely mentioned move from 1024-bit to 2048-bit key lengths in the security demesne … are you ready? More importantly, are your infrastructure and applications ready?

Everyone has likely read about DNSSEC and the exciting day on which the root servers were signed. In response to security concerns – and very valid ones at that – around the veracity of responses returned by DNS, which underpins the entire Internet, the practice of signing responses was introduced. Everyone who had anything to do with encryption and certificates said something about the initiative.

But less mentioned was a move to leverage longer RSA key lengths as a means to increase the security of the encryption of data, a la SSL (Secure Socket Layer). While there have been a few stories on SSL vulnerabilities – Dan Kaminsky illustrated flaws in the system at Black Hat last year – there’s been very little public discussion about the transition in key sizes across the industry. The last time we had such a massive move in the cryptography space was back when we moved from 128-bit to 256-bit keys. Some folks may remember that many early adopters of the Internet had issues with browser support back then, and the impact on the performance and capacity of infrastructure were very negatively impacted.

Well, that’s about to happen again as we move from 1024-bit keys to 2048-bit keys – and the recommended transition deadline is fast approaching. In fact, NIST is recommending the transition by January 1st, 2011 and several key providers of certificates are already restricting the issuance of certificates to 2048-bit keys.

Note that it isn’t just providers who are making this move. Microsoft uses and recommends 2048-bit keys per the NIST guidelines for all servers and other productsRed Hat recommends 2048+ length for keys using RSA algorithm. And as of December 31, 2013 Mozilla will disable or remove all root certificates with RSA key sizes smaller than 2048 bits. That means sites that have not made the move as of that date will find it difficult for customers and visitors to hook up, as it were.    


The impact on organizations that take advantage of encryption and decryption to secure web sites, sign code, and authenticate access is primarily in performance and capacity. The decrease in performance as key sizes increase is not linear, but more on the lines of exponential. For example, though the key size is shifting by a factor of two, F5 internal testing indicates that such a shift results in approximately a 5x reduction in performance (as measured by TPS – Transactions per Second). This reduction in performance has also been seen by others in the space, as indicated by a recent Citrix announcement of a 5x increase in performance of its cryptographic processing. This decrease in TPS is due primarily to heavy use of the key during the handshaking process

The impact on you is heavily dependent on how much of your infrastructure leverages SSL. For some organizations – those that require SSL end-to-end – the impact will be much higher. Any infrastructure component that terminated SSL and re-encrypted the data as a means to provide inline functionality (think IDS, Load balancer, web application firewall, anti-virus scan) will need to also support 2048-bit keys, and if new certificates are necessary these, too, will need to be deployed throughout the infrastructure. 

Any organization with additional security/encryption requirements over and above simply SSL encryption, such as FIPS 140-2 or higher, are looking at new/additional hardware to support the migration.

Note: There are architectural solutions to avoid the type of forklift upgrade necessary, we’ll get to that shortly.

If your infrastructure is currently supporting SSL encryption/decryption on your web/application servers, you’ll certainly want to start investigating the impact on capacity and performance now. SSL with 1024-bit keys typically requires about 30% of a server’s resources (RAM, CPU) and the increase to 2048-bit keys will require more, which necessarily comes from the resources used by the application. That means a decrease in capacity of applications running on servers on which SSL is terminated and typically a degradation in performance.

In general, the decrease we’ve (and others) have seen in TPS performance on hardware should give you a good idea of what to expect on software or virtual network appliances. As a general rule you should determine what level of SSL transaction you are currently licensed for and divide that number by five to determine whether you can maintain the capacity you have today after a migration to 2048-bit keys.

It may not be a pretty picture.


If the advantages of offloading SSL to an external infrastructure component were significant before the move from 1024-bit keys to 2048-bit keys makes them nearly indispensable to maintaining performance and capacity of existing applications and infrastructure. Offloading SSL to an external infrastructure component enabled with specialized hardware further improves the capacity and performance of these mathematically complex and compute intensive processes.

ARCHITECTURAL SOLUTION to support 1024-bit key only applications

If you were thinking about leveraging a virtual network appliance for this purpose, you might want to think about that one again. Early testing of RSA operations using 2048-bit keys on 64-bit commodity hardware shows a capacity in the hundreds of transactions per second. Not tens of thousands, not even thousands, but hundreds. Even if the only use of SSL in your organization is to provide secure web-based access to e-mail, a la Microsoft Web Outlook, this is likely unacceptable. Remember there is rarely a 1:1 relationship between connections and web applications today, and each connection requires the use of those SSL operations, which can drastically impact the capacity in terms of user concurrency.

Perhaps as important is the ability to architect around limitations imposed by applications on the security infrastructure. For example, many legacy applications (Lotus Notes, IIS 5.0) do not support 2048-bit keys. Thus meeting the recommendation to migrate to 2048-bit keys is all but impossible for this class of application. Leveraging the capabilities of an application delivery controller that can support 2048-bit keys, however, allows for the continued support of 1024-bit keys to the application while supporting 2048-bit keys to the client.


That’s a question only you can answer, and you can only answer that by taking a good look at your infrastructure and applications. 

Creative Commons License

Now is a good time to evaluate your SSL strategy to ensure it’s up to the challenge of 2048-bit keys. Check your licenses, determine your current capacity and requirements, and compare those to what can be realistically expected once the migration is complete. Validate that applications currently requiring 1024-bit keys can support 2048-bit keys or whether such a migration is contraindicated by the application, and investigate whether a proxy-based (mediation) solution might be appropriate. And don’t forget to determine whether or not compliance with regulations may require new hardware solutions.

Now this is an F5 Friday post, so you knew there had to be some tie-in, right? Other than the fact that the red-ball glowing ball on every BIG-IP just looks hawesome in the dim light of a data center, F5 solutions can mitigate many potential negative impacts resulting from a migration of 1024-bit to 2048-bit key lengths:

BIG-IP Specialized Hardware

  • BIG-IP hardware platforms include specialized RSA acceleration hardware that improves the performance of the RSA operations necessary to support encryption/decryption and SSL communication and enables higher capacities of the same.

EM (Enterprise Manager) Streamlines Certificate Management

F5’s centralized management solution, EM (Enterprise Manager), allows an organization to better manage a cryptographic infrastructure by providing the means to monitor and manage key expirations across all F5 solutions and collect TPS history and usage when sizing to better understand capacity constraints.

BIG-IP Flexibility

BIG-IP is a full proxy-based solution. It can mediate between clients and applications that have disparate requirements, such as may be the case with key sizes. This allows you to use 2048-bit keys but retain the use of 1024-bit keys to web/application servers and other infrastructure solutions.

Strong partnerships and integration with leading centralized key management and crypto vendors that provide automated key migration and provisioning through open and standards-based APIs and robust scripting capabilities.


Enhance security through DNSSEC to validate domain names. Although it has been suggested that 1024-bit keys might be sufficient for signing zones, with the forced migration to 2048-bit keys there will be increased pressure on the DNS infrastructure that may require a new solution for your DNS systems.


In many ways a change of this magnitude is for Information Security professionals their “Y2K” because such a migration will have an impact on nearly every component and application in the data center. Unfortunately for the security folks, we had a lot more time to prepare for Y2K…so get started, go through the checklist, and get yourself ready to make the switch now before the eleventh hour is upon us.

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Published Sep 10, 2010
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