Professor Ronald Linn Rivest (born 1947, Schenectady, New York) is a cryptographer, and is the Andrew and Erna Viterbi Professor of Computer Science at MIT's Department of Electrical Engineering and Computer Science. He is most celebrated for his work on public-key encryption with Len Adleman and Adi Shamir, specifically the RSA algorithm, for which they won the 2002 ACM Turing Award.

He is also the inventor of the symmetric key encryption algorithms RC2, RC4, RC5, and co-inventor of RC6. The "RC" stands for "Rivest Cipher", or alternatively, "Ron's Code". (RC3 was broken at RSA Security during development; similarly, RC1 was never published.) He also authored the MD2, MD4 and MD5 cryptographic hash functions. On September 25, 2006, he published his invention of the ThreeBallot voting system, an innovative voting system that incorporates the ability for the voter to discern that their vote was counted while still protecting their voter privacy. Most importantly, this system does not rely on cryptography at all. Stating "Our democracy is too important", he simultaneously placed ThreeBallot in the public domain.

Professor Rivest is a member of the National Academy of Engineering, the National Academy of Sciences, and is a Fellow of the Association for Computing Machinery, the International Association for Cryptographic Research, and the American Academy of Arts and Sciences. Together with Adi Shamir and Len Adleman, he has been awarded the 2000 IEEE Koji Kobayashi Computers and Communications Award and the Secure Computing Lifetime Achievement Award. Professor Rivest has received an honorary degree (the "laurea honoris causa") from the University of Rome. He is a Fellow of the World Technology Network and a Finalist for the 2002 World Technology Award for Communications Technology. In 2005, he received the MITX Lifetime Achievement Award.

He earned a Bachelor's degree in Mathematics from Yale University in 1969, and a Ph.D. in Computer Science from Stanford University in 1974. He is a co-author of Introduction to Algorithms (also known as 'CLRS'), a standard textbook on algorithms, with Thomas H. Cormen, Charles E. Leiserson and Clifford Stein. He is a member of the MIT Computer Science and Artificial Intelligence Laboratory (CSAIL) in the Theory of Computation Group, and a founder of its Cryptography and Information Security Group. He was also a founder of RSA Data Security (now merged with Security Dynamics to form RSA Security) and of Peppercoin. Professor Rivest has research interests in cryptography, computer and network security, and algorithms.