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...
2. A message can be 'signed' using a privately held decryption key. Anyone can verify this signature using the corresponding publicly revealed encryption key...

- Rivest, Shamir, Adleman; A method for obtaining digital signatures and public-key cryptosystems; Communications of the ACM; Feb. 1978.