Pseudo public key encryption

Abstract

According to the present invention, a secret key cryptosystem and tamper-proof hardware are used to realize a pseudo public key cryptosystem at a low cost. A trap-door one-way function is substantially realized with the use of tamper-proof hardware. Each user performs communication using equipment provided with hardware having the same capabilities described below. Such hardware retains association between an ID and a key. In response to a request from a user, the hardware issues and stores an ID, and it can perform decryption and generation of a MAC (message authentication code) with a key associated with the ID. A user publishes his ID. When performing encryption, a message sender encrypts a message using the published ID. A third person can perform decryption with the ID only by analyzing the mechanism in the hardware. However, the hardware has a capability of destroying itself when such an act is attempted.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a method and system for a public key encryption, and in particular to a method and system for realizing a pseudo public key cryptosystem at a low cost. BACKGROUND ART [0002] Public key encryption methods, which are especially important among today's encryption techniques, are widely used for encryption, signature and authentication. An algorithm for realizing a public key cryptosystem generally requires a very high cost of calculation. One of practical methods to realize a public key cryptosystem is an RSA cryptography. The RSA cryptography requires an operation of raising a plaintext or a cipher text to the power of the number (an encryption exponent or a decryption exponent) obtained from a value of the Eulerian function of n, which is a product of two large prime numbers and then determining the residue of n, and the cost of this operation is very high. In order to enhance the security of a key, the bit number of n is...

AI Technical Summary

Benefits of technology

[0004] In a first aspect, the present invention provides methods and systems for realizing a pseudo public key cryptosystem at a low cost.

[0008] According to the present invention, a secret key cryptosystem and tamper-proof hardware are used to realize a pseudo public key cryptosystem at a low cost. A trap-door one-way function, which is considered essential for constitution of a public key cryptosystem generally, requires an “expensive” operation. Such a function is substantially realized with the use of tamper-proof hardware. Each user performs communication using equipment provided with hardware having the same capabilities described below. Such hardware retains association between an ID and a key. In response to a request from a user, the hardware issues and stores an ID, and it can perform decryption and generation of a message authentication code (hereinafter referred to as a MAC) with a key associated with the ID. Though this hardware can perform encryption and verification of a MAC with any given ID, it cannot perform decryption and generation of a MAC. A user publishes his ID. When performing encryption, a message sender encrypts a message using the published ID of a message receiver and using hardware having the same capabilities as the receiver's hardware. A person can perform decryption with the ID only by analyzing the mechanism in the hardware. However, the hardware has a capability of destroying itself when such an act is attempted.

Problems solved by technology

An algorithm for realizing a public key cryptosystem generally requires a very high cost of calculation.

The RSA cryptography requires an operation of raising a plaintext or a cipher text to the power of the number (an encryption exponent or a decryption exponent) obtained from a value of the Eulerian function of n, which is a product of two large prime numbers and then determining the residue of n, and the cost of this operation is very high.

However, the cost of calculation required for RSA cryptography with a large bit number is very high.

Though measures such as performing such an operation with dedicated hardware may be taken to seek a high speed, this may impose a development and manufacture cost burden or affect product flexibility.

Because of such a situation, the cost of a cryptosystem using a public key is high, and it is difficult to incorporate it in an apparatus which is inexpensively mass-produced.

However, though the cost of operations required for encryption (scalar multiplication of a point on an elliptic curve defined on a finite body, and the like) is lower in comparison with that of modulo exponentiation, the cryptography similarly requires expensive operations, and therefore, it is still difficult to incorporate it in an apparatus which is inexpensively mass-produced.

However, the nature of the trap-door one-way function in the RSA cryptography and the like is utilized for encryption-decryption of a message, and the cost required for the processing is as high as that of common public key cryptosystems.

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