Some of these standards are products of public competitions among academic cryptography researchers, while others are the result of NSA recommendations. An important standard, known as SHA2, was designed by the NSA and is still trusted by independent cryptographers and software developers worldwide.
NIST withdrew one cryptographic standard, called Dual EC DRGB, after documents provided to news organizations by the former intelligence contractor Edward Snowden raised the possibility that the standard had been covertly weakened by the NSA.
Soon after, a leading cryptography company, RSA, told software writers to stop using the algorithm in a product it sells. The company promised to remove the algorithm in future releases.
Many cryptographers have expressed doubt about NIST standards since the initial revelations were published. One popular encryption library changed its webpage to boast that it did not include NIST-standard cryptography. Silent Circle, a company that makes encryption apps for smartphones, promised to replace the encryption routines in its products with algorithms not published by NIST.
If the NIST review prompts significant changes to existing encryption standards, consumers will not see the benefit immediately. "If the recommendations change, lots of code will need to change," said Tanja Lange, a cryptographer at the University of Technology at Eindhoven, in the Netherlands. "I think that implementers will embrace such a new challenge, but I can also imagine that vendors will be reluctant to invest the extra time."
In Friday's announcement, NIST pointed to its long history of creating standards, including the role it had in creating the first national encryption standard in the 1970s -- the Data Encryption Standard, known as DES. "NIST has a proud history in open cryptographic standards, beginning in the 1970s with the Data Encryption Standard," the bulletin said. But even that early standard was influenced by the NSA.
During the development of DES, the agency insisted that the algorithm use weaker keys than originally intended -- keys more susceptible to being broken by super computers. At the time, Whitfield Diffie, a digital cryptography pioneer, raised serious concerns about the keys. "The standard will have to be replaced in as few as five years," he wrote.
The weakened keys in the standard were not changed. DES was formally withdrawn by the institute in 2005.
The announcement is the latest effort by NIST to restore the confidence of cryptographers. A representative from NIST announced in a public mailing list, also on Friday, that the institute would restore the original version of a new encryption standard, known as SHA3, that had won a recent design competition but altered by the institute after the competition ended. Cryptographers charged that NIST's changes to the algorithm had weakened it.
The SHA3 announcement referred directly to cryptographers' concerns. "We were and are comfortable with that version on technical grounds, but the feedback we've gotten indicates that a lot of the crypto community is not comfortable with it," wrote John Kelsey, NIST's representative. There is no evidence the NSA was involved in the decision to change the algorithm.
The reversal took Matthew Green, a cryptographer at Johns Hopkins University, by surprise. "NIST backed down! I'm not sure they would have done that a year ago," he said.