In a new article in an academic math journal, the NSA’s former director of research says that the agency’s decision not to withdraw its support of the Dual EC_DRBG random number generator after security researchers found weaknesses in it and questioned its provenance was a “regrettable” choice.

Michael Wertheimer, the former director of researcher at the National Security Agency, wrote in a short piece in Notices, a publication of the American Mathematical Society, that even during the standards development process for Dual EC many years ago, members of the working group focused on the algorithm raised concerns that it could have a backdoor in it. The algorithm was developed in part by the NSA and cryptographers were suspect of it from the beginning.

Then, in 2007, well into the life of Dual EC, researchers at Microsoft delivered a talk at a conference that detailed the potential for a backdoor in the algorithm. Still, both the NSA and NIST, which approves technical standards for the United States government, stood by the algorithm. Dual EC was mostly forgotten until late 2013 when allegations emerged that the NSA may have had a secret $10 million contract with RSA Security that prompted the vendor to make Dual EC–which was then known to be weak–the default random number generator in some of its key crypto products. NIST last year removed Dual EC from its guidance on random number generators.

“I wrote about it in 2007 and said it was suspect. I didn’t like it back then because it was from the government,” crypto pioneer Bruce Schneier told Threatpost in September 2013. “It was designed so that it could contain a backdoor. Back then I was suspicious, now I’m terrified.”

NSA should have ceased supporting the dual EC_DRBG algorithm immediately after security researchers discovered the potential for a trapdoor Tweet

The NSA came under heated criticism for the Dual EC episode, and now one of the agency’s top officials has said it was a mistake for the NSA not to have withdrawn its support for the algorithm after the weaknesses were raised years ago.