A San Francisco childhood
Leonard Max Adleman was born on December 31, 1945, in California, into a Jewish family whose roots lay in the area around Minsk, in present-day Belarus, from where his forebears had emigrated to the United States. He grew up in San Francisco, the city he has always been identified with.
Interested in mathematics and science from childhood, he studied mathematics at the University of California, Berkeley, receiving his bachelor’s degree in 1968. His path to research was not direct: he began graduate school elsewhere, left, and worked as a computer programmer at the Federal Reserve Bank in San Francisco before returning to Berkeley for graduate study in electrical engineering and computer science. He completed his doctorate in 1976 under Manuel Blum, a pioneer of the theory of computational complexity.
MIT and the challenge from Stanford
In 1976 Adleman joined the mathematics department of the Massachusetts Institute of Technology. That same year Whitfield Diffie and Martin Hellman at Stanford published New Directions in Cryptography, proposing public-key cryptography: a system in which anyone could encrypt a message with a published key, but only the holder of a matching private key could decrypt it. They had not found a complete practical way to do it.
Adleman’s MIT colleague Ron Rivest was captivated by the problem and enlisted Adi Shamir, a visiting Israeli computer scientist, and Adleman, a number theorist. The division of labour was unusual. Rivest and Shamir proposed schemes; Adleman’s job was to break them. According to the National Inventors Hall of Fame, he broke 42 of them before the trio arrived at one that he could not.
RSA
The system they settled on in 1977, named RSA from their initials, uses a fact about whole numbers. Multiplying two large prime numbers is easy, but no one knows a fast way to reverse the process and find the primes from their product. In RSA, the product forms part of the public key, which can be shared with the world; the primes, kept secret, allow the owner to decrypt messages and to create digital signatures that anyone can check but no one can forge.
The method was published in 1978 in the Communications of the ACM, and MIT received a U.S. patent on it, number 4,405,829, in 1983. That year the three inventors founded RSA Data Security to bring the technology to market; it was sold in 1996 for about 200 million dollars.
One way to picture RSA is as a padlock that anyone can snap shut but only one person can open. The owner hands out open padlocks freely, which is the public key, and keeps the only key that opens them, which is the private key. Anyone wishing to send a secret message locks it with one of the owner’s padlocks; once locked, not even the sender can open it again. The mathematics of prime numbers is what makes the padlock impossible, in practice, to pick: with keys hundreds of digits long, finding the secret primes would take the fastest computers an impractically long time.
Securing the internet
RSA became the world’s most widely used public-key system. The National Inventors Hall of Fame calls it instrumental to the growth of e-commerce and notes that it has been used in almost all internet-based transactions to protect sensitive data such as credit card numbers. When a web browser connects securely to a bank or shop, digital certificates signed with RSA have very often been part of how the browser confirms the site is genuine. RSA signatures also protect software updates, secure email and countless business and government systems.
Its significance lies in solving a problem as old as secret writing itself: how two parties who have never met can communicate privately. Before public-key cryptography, they would first have had to share a secret key through some trusted channel. With RSA, billions of strangers can transact and communicate securely every day.
Naming the computer virus
In 1980 Adleman moved to the University of Southern California in Los Angeles, where he has spent the rest of his career, becoming a Distinguished Professor of computer science. In 1983 one of his students, Fred Cohen, demonstrated a self-replicating program that could spread between computers. In his 1984 paper Experiments with Computer Viruses, Cohen credited Adleman with coining the term computer virus, a name that helped the world understand and defend against a new kind of threat.
Adleman’s work in number theory also continued. With Carl Pomerance and Robert Rumely he developed the Adleman–Pomerance–Rumely primality test, an important step toward fast methods for proving that very large numbers are prime, which matters for generating cryptographic keys.
Cohen’s experiments showed how a program could copy itself into other programs and spread, and his work laid the foundations of the scientific study of computer viruses and of defences against them. The term Adleman suggested, borrowing from biology, captured exactly how such programs behave, and it entered everyday language.
Computing with DNA
In the years after his virus work Adleman turned to biology, studying how HIV affects the immune system’s white blood cells, and he learned the techniques of molecular biology. Struck by the way DNA stores information as long strings of four chemical letters, he wondered whether molecules could compute. In a 1994 paper in Science, Molecular Computation of Solutions to Combinatorial Problems, he showed that they could: he encoded a small instance of the Hamiltonian path problem, a cousin of the travelling salesman problem, in strands of DNA and used laboratory techniques to filter out the wrong answers, leaving the right one.
It was the first computation carried out with DNA, and it founded a new field. In 2002 his group used DNA to solve a 20-variable logic problem with more than a million possible solutions. DNA computing has since grown into the broader field of molecular programming and DNA nanotechnology, which researchers are exploring for applications such as ultra-dense data storage, smart diagnostic tests and drug delivery. Adleman is widely known as the father of DNA computing.
The experiment in 1994 used a network of just seven points, small enough to solve by hand, but its importance lay in the principle. A single test tube can hold trillions of DNA molecules, each of which can take part in a chemical reaction at the same time, an extraordinary degree of parallelism. Adleman opened a laboratory for molecular science at the University of Southern California in the mid-1990s to explore the idea further. While DNA computers have not replaced electronic ones, his demonstration that biological molecules can be programmed has inspired research in synthetic biology, molecular diagnostics and DNA data storage.
Honours and a wide-ranging mind
For the invention of RSA, Adleman, Rivest and Shamir received the Paris Kanellakis Theory and Practice Award in 1996 and the 2002 A.M. Turing Award, often called the Nobel Prize of computing. Adleman was elected to the National Academy of Engineering in 1996 for contributions to the theory of computation and cryptography, and he is a member of the National Academy of Sciences, a Fellow of the American Academy of Arts and Sciences (2006) and an ACM Fellow (2021). In 2018 he was inducted into the National Inventors Hall of Fame.
His interests have always been broad. He served as mathematical consultant on the 1992 film Sneakers, a thriller about codebreaking, and he is an amateur boxer who once sparred with the professional champion James Toney. In recent years he has worked on a mathematical theory he calls Strata.
Colleagues and students describe a scholar who moves easily between pure mathematics, computer science and the laboratory bench, and who has repeatedly been willing to start again as a beginner in a new field.
Jewish roots
Adleman was born into a Jewish family descended from immigrants from the Minsk region of the Russian Empire, part of the great migration of Eastern European Jews to America around the turn of the twentieth century. He grew up in San Francisco and went on, like many descendants of that migration, through public universities into science.
He has not made religious practice a public part of his life story, and published biographies focus on his work.
His story fits a familiar pattern of American Jewish life in the twentieth century: grandparents who fled poverty and persecution in the Russian Empire, and descendants who, within two generations, helped build the technologies of a new age.
Legacy
Leonard Adleman’s place in history is secured twice over. As the codebreaker of the RSA team, he helped give the world a practical public-key system that has protected trillions of dollars in payments and the privacy of billions of people. As the founder of DNA computing, he showed that the molecules of life could also be used to process information, opening a field that still grows today.
He has continued to teach at the University of Southern California for more than four decades, and the field he founded with a single experiment in a test tube now has its own conferences, journals and research centres around the world.
Both achievements came from the same instinct: to take a problem that seemed impossible, attack it from an unexpected direction, and keep going until it gave way.
Sources & further reading
Leonard Adleman, National Inventors Hall of Fame · Leonard Adleman, Wikipedia · Adi Shamir, Wolf Prize Laureate in Mathematics 2024, Wolf Foundation · Jewish Computer and Information Scientists, jinfo.org · Leonard Adleman: The Father of DNA Computing, Stanford University course project · Researched from the sources above and checked against them. Spotted an error? Tell us.
A life of tikkun olam. This is part of tikkun olam, the Jewish idea of repairing the world, and every one of us can add to it.