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SHA1 SHAttered

Researchers have announced the first proven collision of a Secure Hash Algorithm (SHA) 1 hash. Two PDF documents with completely different content both result in the same SHA1 hash when calculated.
Threat ID:
CC-1229
Category:
Threat Severity:
Low
Threat Vector:
Published:
2 March 2017 12:00 AM
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This article no longer conforms to NHS Digital's standards for cyber alerts, and may contain outdated or inaccurate information. Use of this information contained in this page is at your own risk

Summary

Researchers have announced the first proven collision of a Secure Hash Algorithm (SHA) 1 hash. Two PDF documents with completely different content both result in the same SHA1 hash when calculated.

Threat details

This marks the long overdue end of SHA1 leaving many organisations rushing to replace it as the 90 day public disclosure deadline looms.

SHA1 was released in 1995 and was used in browser security, code repositories, file identity security and more. The concept was that a large amount of data can be condensed into a relatively small hash which can be compared with no two pieces of source data resulting in the same hash. A collision occurs when two pieces of source data are put through the hashing function and result I the same hash.

Researchers have been calling for the deprecation for some time after highlighting weaknesses in the algorithm and suggesting collisions could soon become a possibility.

Researchers have now confirmed that, with the use of an unannounced proof of concept method along with huge computational power, they have managed t produce the first SHA1 collision.

The sheer scale of computational power required renders an attack unfeasible for the average attacker. However, this type of attack may not be out of reach for a well-funded Advanced Persistent Threat (APT) group or state sponsored attackers.

Remediation steps

Type Step
  • Migrate to safer cryptographic hashes such as SHA-256 and SHA-3.
  • Be cautious when using third party services that may still use SHA1.

Last edited: 17 February 2020 11:38 am