Niels T. Ferguson (born 10 December 1965, Eindhoven) is a Dutch cryptographer and consultant who currently works for Microsoft. He has worked with others, including Bruce Schneier, designing cryptographic algorithms, testing algorithms and protocols, and writing papers and books. Among the designs Ferguson has contributed to is the AES finalist block cipher algorithm Twofish as well as the stream cipher Helix and the Skein hash function.

In 1999, Niels Ferguson, together with Bruce Schneier and John Kelsey, developed the Yarrow algorithm random number generator. Yarrow was later developed by Niels Ferguson and Bruce Schneier into the Fortuna random number generator.

In 2001, he claimed to have broken the HDCP system that is incorporated into HD DVD and Blu-ray Discs players, similar to the DVDs Content Scramble System, but has not published his research, citing the Digital Millennium Copyright Act of 1998, which would make such publication illegal.

At the CRYPTO 2007 conference rump session, Niels Ferguson and Dan Shumow presented an informal paper describing a weakness in the NIST specified Dual EC DRBG PRNG.