Three Chinese researchers have further refined an attack on the encryption standard frequently used to digitally sign documents, making the attack 64 times faster and leaving cryptographers to debate whether the standard, known as the Secure Hash Algorithm, should be phased out more quickly than planned.

The attack, presented last week at the Crypto conference in Santa Barbara, Calif., would allow a forger to create two documents that return the same digital fingerprint, a short sequence of numbers that represent the contents of a much larger document. While experts debate whether the attack is practical, the trend seems to indicate that the Secure Hash Algorithm (SHA-1) is succumbing to less processor-intensive breaks, said William E. Burr, manager of the the Security Technology Group at the National Institute of Standards and Technology (NIST).

"It is certainly somewhat alarming," Burr said. He likened the rapid advances in attacks on SHA-1 to a submarine under fire. "What we are figuring out right now is whether we have to do a crash dive drill-- where some people might not make it inside before we close the hatch, but at least we will save the ship."

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