But internal memos leaked by a former N.S.A. contractor, Edward Snowden, suggest that the N.S.A. generated one of the random number generators used in a 2006 N.I.S.T. standard — called the Dual EC DRBG standard — which contains a back door for the N.S.A. In publishing the standard, N.I.S.T. acknowledged “contributions” from N.S.A., but not primary authorship.