**Don Coppersmith** (born c. 1950) is a cryptographer and mathematician. He was involved in the design of the Data Encryption Standard block cipher at IBM, particularly the design of the S-boxes, strengthening them against differential cryptanalysis. He has also worked on algorithms for computing discrete logarithms, the cryptanalysis of RSA, methods for rapid matrix multiplication (see Coppersmith–Winograd algorithm) and IBM's MARS cipher. Don is also a co-designer of the SEAL and Scream ciphers.

In 1972, Coppersmith obtained a Bachelor's degree in mathematics at the Massachusetts Institute of Technology, and a Masters and PhD in mathematics from Harvard University in 1975 and 1977 respectively. He was a Putnam Fellow each year from 1968–1971, becoming the first four-time Putnam Fellow in history. In 1998, he started *Ponder This*, an online monthly column on mathematical puzzles and problems. In October 2005, the column was taken over by James Shearer.

In 2002, Coppersmith won the RSA Security Award for Mathematics.