JP2946469B2 - Decryption device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a decoding device, and more particularly to a decoding device that transmits and decodes audio and image signals.

[Conventional technology]

2. Description of the Related Art In recent years, the resolution of images has been improved, and, for example, television images viewed daily, for example, are shifting from the NTSC system to the high-vision system. When such a high-definition image is recorded on a recording medium such as a tape or a disk, or transmitted to a remote place via a satellite, an optical fiber, a cable, or the like,
In consideration of image quality deterioration factors such as S / N and jitter, digital transmission is more advantageous than analog transmission.

On the other hand, digital transmission has the merit that image quality does not deteriorate even if dubbing is repeated many times in a recording system such as a tape or a disk, but on the other hand, illegal copying or duplication is a major social problem. Further, in communication and broadcasting systems such as satellites, optical fibers, and cables, there is a problem that a payer who has not paid a fee or an outsider may view the information.

Conventionally, in such digital transmission, when data is transmitted from a computer or the like, a method has been used in which all data is transmitted after being encrypted, and the receiving side decrypts the data using an encryption key.

Next, conventional examples of such encryption will be described with reference to FIGS. 2 and 3. FIG.

FIG. 2 is a U.S. data encryption standard disclosed in FIPS Publication 46, Jan. 15, 1977.
rd; hereinafter referred to as DES or conventional example)
FIG. 3 is a diagram showing a function which is the center of the encryption of FIG.

This conventional data encryption algorithm has been published as "Data Encryption Standard" as described above.

Hereinafter, this DES (conventional example) will be described with reference to FIGS. 2 and 3. FIG.

First, this DES is a block cipher for binary data consisting of 0 and 1. In DES, encryption is performed by dividing binary data into 64-bit blocks and repeating transposition and substitution for each block. The key is 64 bits, of which 8 bits are check bits for error detection and 56 bits are valid. The key controls each substitution. FIG. 2 shows the process of DES encryption. FIG. 3 shows the function fK which is the center of encryption.
(R) is shown.

In FIG. 2, the 64-bit plaintext is first transposed. This is a fixed transposition independent of the key. Then 64
The bits are divided into a left half _Lo and a right half _Ro . Then 16
Over the steps, Is repeated. Here, + represents the sum of mod2 for each bit. L _n and R _n are 32 bits in the left half and 32 bits in the right half, respectively, after the completion of the operation of the nth stage.

K _n is configured as shown on the right side of Figure 2 from the key. In FIG. 2, s ₁ ,..., S ₁₆ is 1 or 2.
The contracted transposition 2a is to perform transposition except for some of the inputs. In this case, 8 bits are removed from the input 56 bits, and the output becomes 48 bits. The contracted transpose is an irreversible transformation and cannot completely restore the input from the output. This makes key estimation more difficult.

Next, the function fK (R) in FIG. 2 will be described with reference to FIG.

In FIG. 3, in order to create a function fK (R), first, an enlarged transposition 3a is performed on R. Enlarged transposition is to transpose some of the inputs in duplicate. In this case, 16 bits of the 32-bit input appear in the output redundantly. Next, K composed of the key is added to this output
Add with d2. The resulting 48 bits are divided into eight small blocks of 6 bits, and each 6 bits is divided into S ₁ , S ₂ ,
..., it is converted into each 4 bits by S _8. This is 6
If a bit is regarded as one character, it can be considered as a kind of substitution. However, since the output is compressed to 4 bits, this conversion is an irreversible conversion. Therefore, fK
(R) is generally an irreversible function. However, this does not mean that the conversion of the formula (1) is irreversible. In fact, equation (1) is Since it deformed, L _n, it can be seen that _{L n-1, R n-} 1 from R _n can be calculated.

By the way, the operation of the equation (1) is repeated 16 times to obtain L ₁₆ and R _16, and these are finally transposed again to finish the encryption.

 Next, decoding will be described.

Decryption may be performed by performing substantially the reverse operation of encryption. Simply put, it is sufficient to proceed from bottom to top in FIG. First, the inverse transposition of the last transposition of encryption is performed, and R _n-1 and L _n-1 are obtained by the following equation (2). When _Ro and _Lo are obtained, the encryption is performed. If you do the reverse transposition of the first transposition, the original 64
Bit is obtained.

To date, there is no known way to decrypt DES ciphers, except by examining the keys one by one. Now, suppose that it took 1 microsecond for one key to check whether it was the correct key. At this time, 2 ⁵⁶
It takes 2283 years to find all the keys. It takes hundreds of years, even with great luck.

[Problems to be solved by the invention]

As described above, in the conventional example, in the case of a high-definition video image such as a high-definition video, if an analog image signal is simply A / D converted and transmitted, for example, a video signal band of 30 MHz or more should be secured. According to the sampling theorem, sampling must be performed at least at a rate of 60 MHz or higher. When A / D conversion is performed at 74.25 MHz and 8 bits, the transmission rate is 74.25 (MHz) × 8 (bit) = 594 (Mbi
t / s). Therefore, the amount of information is reduced by 1 to save transmission capacity.
Even if it is compressed to / 5, the transmission rate will be about 120 (Mbit / s). There is a problem that it is very difficult to encrypt and transmit such an enormous amount of information in terms of high-speed processing of the encryption unit, the size of hardware, and the cost.

The present invention has been made in order to solve the above problems, and even in an extremely high-speed coded transmission device,
Since confidentiality can be easily maintained and decryption can be performed at a low speed, an LSI or the like that conforms to an encryption standard such as DES can be used. Small-sized, low-cost encryption is performed, and encryption is performed in a decryption table. Therefore, it is an object of the present invention to obtain a decoding device having high confidentiality performance in which transmitted code data cannot be decrypted unless the encryption is completely decrypted.

[Means for solving the problem]

In order to achieve the above object, in the present invention, a decoding device is configured as in the following (1).

(1) a storage unit having a decoding table for decoding an encoded code encoded for data compression, and for decoding encoded data input from an external device using the decoding table; A decryption device comprising: a decryption transfer unit that receives the encrypted decryption table, restores the encrypted decryption table, and transfers the decrypted decryption table to the storage unit.

[Action]

According to the configuration (1), the encrypted decryption table is restored and transferred to the storage unit. In the storage unit, the encoded code coded for data compression is replaced with the decoded code described above. Decrypted using the conversion table.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In this embodiment, a known prior value prediction encoding method (hereinafter referred to as DP
An example is described below.

FIG. 1 is a block diagram of an encoding apparatus according to an embodiment of the present invention. In FIG. 1, A is a storage means,
This is a means composed of a RAM (decoding table) 3, storing the decoding table, and reading out a decoded value from an address determined by the encoded code. B is a restoring transfer unit, which decrypts the cipher (to be described in detail later) when loading a previously encrypted decryption table into the storage unit A, restores the encrypted decryption table, and restores the storage unit A Means to transfer to 1 is a terminal to which the transmitted DPCM code Yi is inputted, 2 is an output terminal, and RAM3 which constitutes a decoding table
Is the DPCM code Yi and the predicted value Xi
(Described later) is input. Reference numeral 5 denotes a decryption device (to be described later), and reference numeral 6 denotes an external storage device that stores a previously encrypted decryption table.

 Next, the operation of this embodiment will be described with reference to FIG.

In FIG. 1, first, a key for decrypting a code is input to a terminal 7 and output to a decryption device 5. After the input of the decryption key is completed, the encrypted decryption table is output to the decryption device 5 from the external storage device 6 that stores the decryption table encrypted in advance.
The decryption device 5 restores the decryption table encrypted based on the above key. This restored decoding table is sequentially RA
Loaded to M3 (details described later).

When the DPCM code Yi and the predicted value Xi are input, the RAM 3 outputs the corresponding decoded value in the loaded table to the output terminal 2 at the memory access time. The decoded value output from the RAM 3 is also applied to the D flip-flop 4. D
The output of the flip-flop 4 is the RAM3 as the predicted value Xi.
Is applied to

For example, if the DPCM code Yi is 4 bits, the decoded value output from the RAM 3 is 8 bits, and the predicted value Xi output from the D-type flip-flop 4 is 8 bits, the capacity of the RAM 3 is 4K × 8 bits.
For a total of 32Kbit. Now, if an LSI that decrypts at 1 Mbit / sec is used, it will be able to decrypt in 0.032 seconds.

Also, since the input data Yi is not encrypted, it can be decrypted at high speed as before. It should be noted that if a ROM card or a magnetic card is used as the storage device, the decryption table is mailed to the recipient, and key information for decryption is separately transmitted, so that the key can be easily changed.

In this embodiment, the description has been given of the example of the predictive prediction coding.However, if the decoding table is stored in the storage device and transferred to the decoding RAM to perform the decoding, the coding method may be changed. In addition, encryption can be easily performed by another encoding method such as vector quantization.

〔The invention's effect〕

As described above, according to the present invention, even in an extremely high-speed coded transmission device, confidentiality can be easily maintained, and decryption is performed at a low speed. An LSI or the like can be used, and encryption can be performed at a small size and at a low price.

Further, since encryption is performed on the decryption table, the transmitted code cannot be decrypted unless the encryption is completely decrypted, and a transmission device with high confidentiality performance can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram of an encoding apparatus according to an embodiment of the present invention, FIG. 2 is a flowchart showing encryption in a conventional example, and FIG. 3 is a diagram showing a function which is the center of the encryption in FIG. It is. A: storage means B: restoration transfer means 1, 7, terminal 3: RAM 4: DF / F 5: decryption device 6: external storage device

Claims (1)

(57) [Claims] 1. A storage means for decoding a coded code coded for data compression by decoding the coded data inputted from an external device using the above-mentioned decoding table. And a restoring / transferring means for inputting the encrypted decryption table, restoring the encrypted decryption table and transferring the decrypted decoding table to the storage means.