Pierluigi Paganini
February 24, 2017
Researchers at Google and Centrum Wiskunde & Informatica (CWI) in the Netherlands succeeded in conducting the first real world collision attack against popular SHA-1 hashing algorithm.
The researchers created two documents with different content but having the same SHA-1 hashes.
Google and CWI devised a hacking method dubbed ‘SHA-1 shattered’ or ‘SHAttered.’
“We were able to find this collision by combining many special cryptanalytic techniques in complex ways and improving upon previous work. In total the computational effort spent is equivalent to 2 63.1 SHA-1 compressions and took approximately 6 500 CPU years and 100 GPU years,” experts wrote in the research paper.
The SHA-1 algorithm was designed in 1995 by the National Security Agency (NSA) as a part of the Digital Signature Algorithm, as we have already explained in the past hashing functions converts any input message to a string of numbers and letters of fixed length. This string is theoretically unique and is normally used as a cryptographic fingerprint for that message.
If two different messages generate the same digest we are in the presence of a collision, this circumstance opens the door to hackers. A successful collision attack could be exploited by hackers to forge digital signatures.
In 2015 a group of researchers demonstrated that the cost of breaking the SHA-1 hash algorithm is lower than previously estimated.
The experts evaluated the economic effort requested to break the SHA1-1, experts in a range from $75,000 and $120,000 using Amazon’s EC2 cloud over a period of a few months.
According to the experts, the SHAttered attack is 100,000 times faster than a brute-force attack, it required nine quintillion (9,223,372,036,854,775,808) computations.
The SHAttered attack was composed of two phases:
The monetary cost of computing the second block of the attack by renting Amazon instances can be estimated from these various data. According to the experts, it would cost roughly $560,000 for the necessary 71 device years. It would be more economical for a patient attacker to wait for low “spot prices.”
The experts used two PDF files with different content for their PoC, the two documents had the same SHA-1 hash.
The researchers will release the code of the attack after 90 days.
The experts released a free online tool that scans for SHA-1 collisions in documents, it is available on the shattered.io website. Google has already introduction mitigation solutions in both Gmail and Google Drive services.
I suggest you give a look at this interesting infographic on the SHAttered attack.
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(Security Affairs – SHAttered attack, SHA-1)
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