JPH11112492A - Ciphering and deciphering system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow only a receiver to decipher a cryptogram by his own characteristic key by opening the time series of a chaos of low resolution for the ciphering of a transmitting person and using the time series of a chaos of high resolution for the deciphring of a receiving person. SOLUTION: A chaos generating circuit repeats nonlinear one-dimensional mapping to generate the time series Y16 (t)-t of a chaos. Its low-ordered 8 bits are omitted to obtain the time series Y8 (t)-t of high-ordered 8 bits. The time series Y16 (t)-t is a ciphering table only for a receiving side and is not opened. The time series Y8 (t)-t is opened to plural transmitters. The assignment of an input code is decided so that the predictable range of Y8 (t)-t may be τ=4. The assignment of the input code is a ciphering key. The side of the receiving person adds a low order bit, (01111111) near a center value, e.g. to a cipher code Y8 (t-τ to obtain a right deciphering code on Y16 (t)-t.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION In today's developed electronics industry, there are increasing opportunities to exchange information bidirectionally. This technology requires two-way confidential communication not only between networks connected by computers but also between various information electronic devices including mobile phones and televisions. The present invention relates to an encryption restoration system using chaos, in which an encryption key and an encryption table are disclosed and given to an information provider, and only a receiver can restore a ciphertext with its own unique key.

[0002]

2. Description of the Related Art By repeating the mapping of a one-dimensional mapping circuit, a time series y (t) -t of an internal state y (t) is obtained.
Is obtained. The measurement of the internal state is performed using a linear quantizer (AD converter), and the internal state y (t) is a quantized value of the digital value Y (t). That is, the internal state is quantized according to the resolution of the AD converter.
A chaotic time series need not necessarily be generated experimentally. The time series may be obtained by a one-dimensional mapping function or a one-dimensional mapping circuit by numerical calculation with sufficient accuracy.

[0003] Time series Y quantized and measured
By searching (t) -t along the discrete time axis t, the transfer characteristic Y (t) -Y (t ± τ) is obtained.
Here, τ is an integer, with a positive sign indicating a step toward the future and a negative sign indicating a return to the past.

When Y (t) is an input code to be encrypted, Y (t−τ) is an encryption code. There are ideally ^2t types of cryptographic codes due to branching into the past.

A value Y (t−τ + τ) advanced by τ steps on the time series with respect to the encryption code Y (t−τ) becomes a restoration code. The internal state Y (t) is determined deterministically toward the future, but has a spread due to divergence and convergence. The maximum width of the spread is ideally ^2t bits. 2
^It may be said that the reduction of ^t bits occurs.

[0006] The number of input codes allowed is limited to the degeneracy. As many input codes as quantum independent of each other are defined, and the length is the length of block division of the digital code string to be encrypted.

A conventional encryption / recovery system that generates an encryption code Y (t−τ) by searching a chaos time series Y (t) −t and obtains a recovery code from Y (t−τ + τ) It is assumed that encryption and restoration are performed on one chaos time series. The chaos time series is an encryption table, and the encryption key is how to assign input codes.

[0008]

[Problems to be Solved by the Invention] Have a common secret key,
It is said that an encryption method having a common encryption table lacks robustness between two remote parties. This is because sending a secret key or an encryption table with a large amount of data via a public line involves various dangers.

[0009] It is shown that a public key system for exposing an encryption key or an encryption table to a plurality or an unspecified number of senders can be provided from the essential properties (perfect order, incompleteness) of a chaotic time series. This is the issue of the present invention.

[0010]

A chaotic time series measured at a high resolution becomes a time series with a low resolution simply by discarding lower bits.

For example, a high resolution refers to a time series measured using a 16-bit AD converter, and an 8-bit time series in which lower 8 bits are discarded can be an example of a time series having a lower resolution.

[0012] Chaos has a predictable range. It is represented by a discrete time t and also depends on the resolution of the chaotic time series.

For example, in an 8-bit resolution time series, the maximum predictable range is seven. Further, at 16-bit resolution, the maximum predictable range is 15.

The predictable range also depends on how the input codes are assigned.

When the discrete time τ reciprocating in the time series exceeds a predictable range, an error occurs in the restoration code, and the original text cannot be completely restored.

A time series of chaos collected at a high resolution and a time series of a low resolution obtained by truncating lower bits are prepared. The low-resolution time series is a public cipher table.

An allocation code is given to an open time series based on the block length of the block division of the digital code string to be encrypted, and the allocation code becomes an encryption key. This encryption key is also made public to the sender.

Since both the cipher table and the encryption key to be disclosed are provided to the sender side as software, it is a feature of the present invention that the sender side can use the encryption without being aware of chaos and encryption.

The step τ of returning to the past when the cryptographic code Y (t−τ) is found by search is longer than the predictable range of the low-resolution time series and is larger than the predictable range of the high-resolution time series. Set shorter.

When restoring the encryption code Y (t−τ) on the receiving side, a high-resolution time series is searched by adding lower bits, and Y (t−τ + τ) is found to obtain a restoration code. The lower additional bits are an encryption key unique to the receiving side.

[0021]

In the transmitting side having a low-resolution time series as a public cipher table, or even when a third party attempts to restore a cipher code using the public cipher table, the chaos exceeds the predictable range of chaos. Restoration fails because the encryption code has been generated.

The receiving side has the value of the lower bit to be added as an encryption key, adds the lower bit to the transmitted encryption code, searches the time series with high resolution, and finds the correct Y (t− (τ + τ), a restoration code can be generated, and correct restoration is guaranteed.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A chaotic circuit represented by an internal state y (t) is generated by repeating a nonlinear one-dimensional mapping in a chaos generating circuit constituted by an integrated circuit. The internal state y (t) of chaos generates a time series Y ₁₆ (t) -t using, for example, an AD converter with 16-bit resolution. Suffix 16
Means a digital code measured at 16-bit resolution.

For example, the lower 8 bits of the time series Y ₁₆ (t) -t are discarded, and a time series Y ₈ (t) -t of only the upper 8 bits is obtained.

The time series Y ₁₆ (t) -t is not disclosed in an encryption table dedicated to the receiving side. Time Series Y
₈ (t) -t is open to multiple senders. Y
Making Y ₈ (t) -t from ₁₆ (t) -t is easy, but making Y ₁₆ (t) -t from Y ₈ (t) -t is hopelessly difficult. .

The predictable range of Y ₈ (t) -t is τ = 4
Determine the input code assignment so that The assignment of the input code is an encryption key, which may also be disclosed to the sender.

When the sender searches for Y ₈ (t) −t to generate an encryption code Y ₈ (t−τ), the value of τ is greater than 4, for example, τ = 5,6,7. Set the software to send to the sender so that you can select one. Since the value of τ is set uniquely on the receiver side, it can be said to be one of the keys unique to the receiver.

For example, an encryption code Y generated at τ = 6
₈ (t-6) is converted to an 8-bit time series Y ₈ (t)-
Even if Y ₈ (t−6 + 6) is found by searching on t, correct restoration code is included due to the divergence of chaos into the future, but incorrect restoration code is also generated and the correct original text is reproduced. Can not.

On the receiver side, the transmitted encryption code Y ₈
(T−τ), lower bits, for example, near the center value (011
11111) can be designed in advance so that a correct restoration code can be obtained on Y ₁₆ (t) −t.

[0030]

As described above, the chaotic encryption / decompression system using the shared secret key system uses a non-linearly quantized time series having the same quantum size, and utilizes an order with high chaos integrity.
On the other hand, the open encryption recovery system of the present invention using the linearly quantized time series extracts and utilizes the imperfect order between time series with different chaos resolutions.

In the restoration result of the present invention using chaos, which is restored at a low resolution, a correct restoration code and an erroneous restoration code are mixed. Therefore, it is not suitable for encrypting information, such as a document, in which the meaning of the document can be inferred from the context before and after the human recognition ability.

This is particularly effective when correctness is required for all numerical values and character arrangements, such as numerical data, for example, a code number and an encryption key assignment code. This is a technique that is particularly effectively used for distributing an encryption key in a common secret key encryption recovery system.

Claims (1)

[Claims] 1. An encryption restoration system that searches for a chaotic time series, generates an encryption code using a branch to the past, and performs recovery using a deterministic property for the future, has a low resolution. A public key cryptosystem characterized by preparing a time series and a high-resolution time series, exposing the low-resolution time series for sender encryption, and using the high-resolution time series for receiver recovery Restore system.