Patent ID: 9160728
Filing Date: 2015-10-13
Classification: H04L

Abstract:
1. A message decryption method performed by a computer including a processor and a memory, the method comprising the steps of: receiving a first communication including: a ciphertext M of a mail m generated using a public encryption key pk_e of a recipient, and a process result of an obfuscated sign-then-encrypt program, said process result in turn comprising: sending, in response to the first communication, information about a sender of the mail m and said recipient of the mail m; receiving a public verification key pk_s of the sender of the mail m and a secret decryption key sk_e of the recipient of the mail m, said secret decryption key sk_e corresponding to the public encryption key pk_e of said recipient of the mail m; decrypting the mail m from the ciphertext M; decrypting the encrypted random number R with said secret decryption key sk_e to obtain said original random number r; calculating said signature s from the randomized signature s′, the mail m and the original random number r obtained from decrypting the encrypted random number R; and verifying the signature s by calculating a signature verification result using the public verification key pk_s of the sender.