Opinion: Cryptanalysis of MD5 and SHA: Time for a new standard
Crypto researchers report weaknesses in common hash functions
Computerworld - At the Crypto 2004 conference in Santa Barbara, Calif., this week, researchers announced several weaknesses in common hash functions. These results, while mathematically significant, aren't cause for alarm. But even so, it's probably time for the cryptography community to get together and create a new hash standard.
One-way hash functions are a cryptographic construct used in many applications. They are used with public-key algorithms for both encryption and digital signatures. They are used in integrity checking. They are used in authentication. They have all sorts of applications in a great many different protocols. Much more than encryption algorithms, one-way hash functions are the workhorses of modern cryptography.
In 1990, Ron Rivest invented the hash function MD4. In 1992, he improved on MD4 and developed another hash function: MD5. In 1993, the National Security Agency published a hash function very similar to MD5, called the Secure Hash Algorithm (SHA). Then in 1995, citing a newly discovered weakness that it refused to elaborate on, the NSA made a change to SHA. The new algorithm was called SHA-1. Today, the most popular hash function is SHA-1, with MD5 still being used in older applications.
One-way hash functions are supposed to have two properties. One, they're one-way. This means that it's easy to take a message and compute the hash value, but it's impossible to take a hash value and re-create the original message. (By "impossible," I mean "can't be done in any reasonable amount of time.") Two, they're collision-free. This means that it's impossible to find two messages that hash to the same hash value. The cryptographic reasoning behind these two properties is subtle, and I invite curious readers to learn more in my book Applied Cryptography.
Breaking a hash function means showing that either -- or both -- of those properties aren't true. Cryptanalysis of the MD4 family of hash functions has proceeded in fits and starts over the past decade or so, with results against simplified versions of the algorithms and partial results against the whole algorithms.
This year, Eli Biham and Rafi Chen, and separately Antoine Joux, announced some pretty impressive cryptographic results against MD5 and SHA. Collisions have been demonstrated in SHA. And there are rumors, unconfirmed at this writing, of results against SHA-1.
The magnitude of these results depends on who you are. If you're a cryptographer, this is a huge deal. While not revolutionary, these results are substantial advances in the field. The techniques described by the researchers are likely to have other applications, and we'll be better able to design secure systems
- The Pivotal Big Data Suite- Reducing the Risks of Big Data The explosion of big data and the rapid evolution of big data tools and technologies is challenging IT to meet the demands of...
- A Survival Guide for Data in the Wild All corporate data used to reside in the data center. Safe and sound behind the corporate firewall. But now, employees have multiple devices...
- Transforming Security: Designing a State-of-the-Art Extended Team The information security mission is no longer about implementing and operating controls.
- The Big Data Security Analytics Era Is Here New security risks and old security challenges often overwhelm legacy security controls and analytical tools.
- What should I look for in a Next Generation Firewall? SANS Provides Guidance With so many vendors claiming to have a Next Generation Firewall (NGFW), it can be difficult to tell what makes each one different....
- Responding to New SSL Cybersecurity Threat The featured Gartner research examines current strategies to address new SSL cybersecurity threats and vulnerabilities. All Security White Papers | Webcasts
Our new bimonthly Internet of Things newsletter helps you keep pace with the rapidly evolving technologies, trends and developments related to the IoT. Subscribe now and stay up to date!