SHA1, one of the Internet's most crucial cryptographic algorithms, is so weak to a newly refined attack that it may be broken by real-world hackers in the next three months, an international team of researchers warned Thursday.
SHA1 has long been considered theoretically broken, and all major browsers had already planned to stop accepting SHA1-based signatures starting in January 2017. Now, researchers with Centrum Wiskunde & Informatica in the Netherlands, Inria in France, and Nanyang Technological University in Singapore have released a paper that argues real-world attacks that compromise the algorithm will be possible well before the cut-off date. The results of real-world forgeries could be catastrophic since the researchers estimate SHA1 now underpins more than 28 percent of existing digital certificates.
Hashing it out
SHA1 is what's known as a cryptographic hash function. Like all hash functions, it takes a collection of text, computer code, or other message input and generates a long string of letters and numbers that serve as a cryptographic fingerprint for that message. Even a tiny change, such as the addition or deletion of a single comma in a 5,000-word e-mail, will cause a vastly different hash to be produced. Like all fingerprints, the resulting hash is useful only as long as it's unique. The moment two different message inputs produce the same hash, the so-called collision can open the door to signature forgeries that can be disastrous for the security of banking transactions, software downloads, and website communications.