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The Prime Number Vault: How Three MIT Scientists Built the Lock on the Modern Internet

Multiplying two massive prime numbers takes a fraction of a second on a computer; factoring that product back into its original primes takes millions of years. By anchoring asymmetric encryption to the asymmetry of prime numbers, Ron Rivest, Adi Shamir, and Leonard Adleman created RSA—the cryptographic algorithm that encrypts every browser connection, banking transfer, and software update on Earth.

Author
Ronald L. Rivest et al.
Published
1978
Journal
Communications of the ACM
Last updated
September 2026
The Prime Number Vault: How Three MIT Scientists Built the Lock on the Modern Internet

Following Diffie and Hellman's theoretical concept of public-key cryptography, the computer science community lacked a practical mathematical function to build a working system. The world needed an elegant mathematical one-way street: an operation that is trivial to perform in one direction but impossible to reverse.

Three MIT researchers discovered the answer in ancient prime number arithmetic: the RSA algorithm. Multiplying two giant 300-digit prime numbers together takes a computer a millisecond, but taking the resulting product and figuring out which two primes created it would take all the supercomputers on Earth millions of years.

RSA became the most widely deployed security algorithm in human history. By securing the green padlock in every web browser, by preventing identity fraud through unforgeable digital signatures, and by protecting trillions of dollars in daily electronic commerce, RSA underpins the security of modern civilization.

Reference

Rivest, R. L., Shamir, A., & Adleman, L. (1978). A method for obtaining digital signatures and public-key cryptosystems. Communications of the ACM, 21(2), 120–126.

Title

A method for obtaining digital signatures and public-key cryptosystems

Abstract

An encryption method is presented with the novel property that publicly revealing an encryption key does not thereby reveal the corresponding decryption key. This has two important consequences: (1) Couriers or other secure means are not needed to transmit keys, since a message can be enciphered using an encryption key publicly revealed by the intented recipient. Only he can decipher the message, since only he knows the corresponding decryption key. (2) A message can be “signed” using a privately held decryption key. Anyone can verify this signature using the corresponding publicly revealed encryption key. Signatures cannot be forged, and a signer cannot later deny the validity of his signature. This has obvious applications in “electronic mail” and “electronic funds transfer” systems. A message is encrypted by representing it as a number M, raising M to a publicly specified power e, and then taking the remainder when the result is divided by the publicly specified product, n, of two large secret primer numbers p and q. Decryption is similar; only a different, secret, power d is used, where e * d ≡ 1(mod (p - 1) * (q - 1)). The security of the system rests in part on the difficulty of factoring the published divisor, n.

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