“A Method for Obtaining Digital Signatures and Public-Key Cryptosystems” is the paper by Ronald L. Rivest, Adi Shamir, and Leonard Adleman that introduced the RSA cryptosystem. It was published in Communications of the ACM and is hosted on Rivest’s own MIT page.
The paper sets out the requirements for a public-key system: that encryption and decryption be efficient, that revealing the encryption key not reveal the decryption key, and that a message encrypted and then decrypted return the original. It then presents a concrete construction meeting these goals, built on modular exponentiation and the properties of large prime numbers.
A central contribution of the paper is its treatment of digital signatures. The authors show that a user can “sign” a message by transforming it with their private key, so that anyone holding the corresponding public key can verify both the message’s origin and its integrity. This made RSA useful not only for secrecy but for authentication.
The paper argues that the system’s security depends on the difficulty of factoring large numbers, and discusses the state of factoring methods known at the time. It became one of the most influential publications in cryptography and remains a primary reference for the field.