3021	 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 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. 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 mod p- q- . the security of the system rests in part on the difficulty of factoring the published divisor n. digital signatures public-key cryptosystems privacy authentication security factorization prime number electronic mail message-passing electronic funds transfer cryptography.
