Cryptographic communication method and system

• US 6,377,688 B1
• Filed: 12/31/1997
• Issued: 04/23/2002
• Est. Priority Date: 04/28/1997
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Numao, Masayuki
• Primary Examiner(s): Peeso, Thomas R.
• Application Number:
  US09/001,874
• Time in Patent Office: 1,574 Days
• Field of Search: 380/30, 713/200, 713/201
• US Class Current: 380/30
• CPC Class Codes: H04L 2209/08 Randomization, e.g. dummy operations or using noise
• CPC Class Codes: H04L 9/302 involving the integer factorization problem, e.g. RSA or quadratic sieve [QS] schemes

Abstract

The object of the present invention is to provide a cryptographic communication system that maintains a high level of information security without a sender and a receiver being required to manage a secret key. According to the system of the present invention, a dedicated decryption server that has a secret key is employed in addition to a transmitter used by a sender and a receiver used by a recipient. While the presence of nonencrypted messages in the server is precluded, the server can decrypt an encrypted message and send the decrypted message to an authorized receiver.

Claims

1. A cryptographic communication system having a transmitter, a receiver and a server, wherein said system being characterized in that:

(1) said server has means for creating a pair of public keys (P, N) and a secret key S, and means for opening said public keys to the public;

(2) said transmitter has means for encrypting a message M using said public keys (P, N) as a message M0, and means for sending said message M0 to said receiver;

(3) said receiver has means for encrypting said message M0 using a specified random number X_R as a message M1, and means for sending said message M1 to said server;

(4) said server has means for decrypting said message M1 using said secret key S as a message M2, and means for sending said message M2 to said receiver; and

(5) said receiver has means for decrypting said message M2 using said specified random number X_R as a message M3.

6. The system according to one of claims 1 through 4, wherein RSA encryption relational equations are established between said public keys (P, N) and said secret key S and wherein said M0, M1, M2 and M3 are represented as:

$\begin{array}{c}\mathrm{M0}=\text{\hspace{1em}<br><br>}<br><br>M^P<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{mod}<br><br>\text{\hspace{1em}<br><br>}<br><br>N\\ \mathrm{M1}=\text{\hspace{1em}<br><br>}<br><br>\left(X_R^P<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{mod}<br><br>\text{\hspace{1em}<br><br>}<br><br>N\right)*\mathrm{M0}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{mod}<br><br>\text{\hspace{1em}<br><br>}<br><br>N\\ =\text{\hspace{1em}<br><br>}<br><br>{\left(X_R*M\right)}^P<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{mod}<br><br>\text{\hspace{1em}<br><br>}<br><br>N\\ \mathrm{M2}=\text{\hspace{1em}<br><br>}<br><br>{\left(\mathrm{M1}\right)}^{\mathrm{PS}}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{mod}<br><br>\text{\hspace{1em}<br><br>}<br><br>N\\ =\text{\hspace{1em}<br><br>}<br><br>{\left(X_R*M\right)}^{\mathrm{PS}}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{mod}<br><br>\text{\hspace{1em}<br><br>}<br><br>N\\ =\text{\hspace{1em}<br><br>}<br><br>X_R*M\\ \mathrm{M3}=\text{\hspace{1em}<br><br>}<br><br>\mathrm{M2}*\left(X_R^{-1}\right)<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{mod}<br><br>\text{\hspace{1em}<br><br>}<br><br>N\\ =\text{\hspace{1em}<br><br>}<br><br>M.\end{array}$

7. The system according to claim 6, wherein said specified random number X_R is a prime number.

8. The system according to claim 6, wherein said specified random number X_R is a composite number composed of a product of a plurality of numbers.

2. A lottery system using cryptographic communication having a plurality of transmitters, a receiver and a server, said system being characterized in that:

(1) said server has means for creating a pair of public keys (P, N) and a secret key S, and means for opening said public keys to the public;

(2) said plurality of transmitters each have means for encrypting an identifier M assigned for each transmitter using said public keys (P, N) as an identifier M0, and means for sending said identifier M0 to said receiver;

(3) said receiver has means for encrypting said identifiers M0 using a specified random number X_R as a plurality of identifiers M1, and mean for sending said identifiers M1 to said server;

(4) said server has means for selecting one of said identifiers M1 and decrypting a selected identifier M1 using said secret key S as an identifier M2, and means for sending said identifier M2 to said receiver; and

(5) said receiver has means for decrypting said identifier M2 using said specified random number X_R as an elected identifier M3.

3. A public tender system having a plurality of transmitters, a receiver and a server, said system being characterized in that:

(1) said server has means for creating a pair of public keys (P, N) and a secret key S, and means for opening said public keys to the public;

(2) said plurality of transmitters each have means for encrypting a contract price M assigned for each transmitter using said public keys (P, N) as a contract price M0, and means for sending said contract price M0 to said receiver;

(3) said receiver has means for encrypting said contract prices M0 using a specified random number X_R as a plurality of contract prices M1, and means for sending said contract prices M1 to said server;

(4) said server has means for, as soon as it is time for opening, decrypting all of said contract prices M1 using said secret key S as contract prices M2, and means for sending said contract prices M2 to said receiver; and

(5) said receiver has means for decrypting said contract prices M2 using said specified random number X_R as a plurality of contract prices M3.

4. An encrypted message delivery service system having a transmitter, a receiver and a server, said system being characterized in that:

(1) said server has means for creating pairs of multiple public keys and a secret key S, and means for opening said public keys to the public;

(2) said server has means for registering said transmitter at said server, and means for issuing in advance a certificate that includes a transmitter ID, a receiver ID and public keys (P, N) uniquely selected from multiple pairs of said public keys and assigned to said transmitter;

(3) said transmitter has means for encrypting a message M using said public keys (P, N) as a message M0, and means for sending said message M0 with said certificate to said receiver;

(4) said receiver has means for encrypting said message M0 using a specified random number X_R as a message M1, means for adding a signature to said message M1, and means for sending said message M1 with said certificate to said server;

(5) said server has means for opening said signature to verify that said receiver is an authorized receiver described in said certificate, and means for, when said receiver is authorized as an authorized receiver, decrypting said message M1 using said secret key S as a message M2 and sending said message M2 to said receiver; and

(6) said receiver has means for decrypting said message M2 using said specified random number X_R as a message M3.

5. A cryptographic communication method between a transmitter, a receiver and a server, said method comprising the steps of:

(1) said server creating a pair of public keys (P, N) and a secret key S, and opening said public keys to the public;

(2) said transmitter encrypting a message M using said public keys (P, N) as a message M0, and sending said message M0 to said receiver;

(3) said receiver encrypting said message M0 using a specified random number X_R as a message M1, and sending said message M1 to said server;

(4) said server decrypting said message M1 using said secret key S as a message M2, and sending said message M2 to said receiver; and

(5) said receiver decrypting said message M2 using said specified random number X_R as a message M3.

9. The method according to claim 5, wherein RSA encryption relational equations are established between said public keys (P, N) and said secret key S and wherein said M0, M1, M2 and M3 are represented as:

$\begin{array}{c}\mathrm{M0}=\text{\hspace{1em}<br><br>}<br><br>M^P<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{mod}<br><br>\text{\hspace{1em}<br><br>}<br><br>N\\ \mathrm{M1}=\text{\hspace{1em}<br><br>}<br><br>\left(X_R^P<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{mod}<br><br>\text{\hspace{1em}<br><br>}<br><br>N\right)*\mathrm{M0}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{mod}<br><br>\text{\hspace{1em}<br><br>}<br><br>N\\ =\text{\hspace{1em}<br><br>}<br><br>{\left(X_R*M\right)}^P<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{mod}<br><br>\text{\hspace{1em}<br><br>}<br><br>N\\ \mathrm{M2}=\text{\hspace{1em}<br><br>}<br><br>{\left(\mathrm{M1}\right)}^{\mathrm{PS}}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{mod}<br><br>\text{\hspace{1em}<br><br>}<br><br>N\\ =\text{\hspace{1em}<br><br>}<br><br>{\left(X_R*M\right)}^{\mathrm{PS}}<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{mod}<br><br>\text{\hspace{1em}<br><br>}<br><br>N\\ =\text{\hspace{1em}<br><br>}<br><br>X_R*M\\ \mathrm{M3}=\text{\hspace{1em}<br><br>}<br><br>\mathrm{M2}*\left(X_R^{-1}\right)<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{mod}<br><br>\text{\hspace{1em}<br><br>}<br><br>N\\ =\text{\hspace{1em}<br><br>}<br><br>M.\end{array}$

10. The method according to claim 5, wherein said specified random number X_R is a prime number.

11. The method according to claim 5, wherein said specified random number X_R is a composite number composed of a product of a plurality of numbers.