A Method for Obtaining Digital Signatures and Public-Key Cryptosystems

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 intended 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 prime 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.