JPH048034A - decoding device - Google Patents

Abstract

PURPOSE:To realize this decoder with high secrecy performance by using a restoration transferring means so as to decipher a cryptographic code and restoring a ciphered deciphering table when the deciphering ciphered in advance is loaded to a storage means. CONSTITUTION:A key to decipher the cryptographic code is inputted to a terminal 7 and the key is outputted to a cryptographic code deciphering device 5. A ciphered deciphering table is outputted from an external storage device 6 storing the ciphered deciphering table in advance to the cryptographic code deciphering device 5. The device 5 deciphers the ciphered deciphering table based on the key.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a decoding device, particularly a decoding device that transmits and decodes audio and image signals.

(Prior Art) In recent years, images have become increasingly high-definition, and for example, the television images that we use on a daily basis are shifting from the NTSC system to the high-definition system. When recording such high-definition images on recording media such as tapes and disks, or transmitting them to remote locations via satellites, optical fibers, cables, etc., S
Considering image quality deterioration factors such as /N and jitter, digital transmission is more advantageous than analog transmission.

On the other hand, digital transmission has the advantage of not causing deterioration in image quality no matter how many times dubbing is repeated in recording systems such as tapes and disks, but on the other hand, illegal copying and duplication pose a major social problem. In addition, communications such as satellites, optical fibers and cables,
In the broadcasting system, there is a problem in that people who have not paid their fees or people outside the party are able to watch and listen to the video in secret.

Therefore, in conventional digital transmission, when transmitting data from a computer or the like, a method has been used in which all the data is encrypted before being sent, and the receiving side decrypts it using an encryption key.

Next, conventional examples of these encryption methods will be explained using FIGS. 2 and 3.

Figure 2 of the drawing is from FIPS Publication 4 dated January 15, 1977.
The US data encryption standard disclosed in
encryption 5 standard ;hereinafter DES
FIG. 3 is a diagram showing a function that is the center of the encryption in FIG. 2.

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

This DES (conventional example) will be explained below with reference to FIGS. 2 and 3.

First, this DES is a block cipher for binary data consisting of 0.1. In DES, 27c data is 64
It is divided into blocks of bits, and each block is encrypted by transposing the block and turning the upper half of the block around. The key is 64
Of these, 8 bits are check bits for error detection, and 56 bits are valid. This key controls the first half of each round. The second drawing is DES
The process of encryption is shown. Further, FIG. 3 shows (R) as a function f which is the center of encryption.

In Figure 2 of the drawing, the 64-bit plaintext is first transposed. This is a fixed transposition that is independent of the key. Next 6
The 4 bits are divided into a left half L0 and a right half R. After that, the calculation is repeated for 16 stages. Here, + represents the sum of m o d 2 for each human.

Also, Ln.

Rn is the left half of 3 when the nth stage of calculation is completed.
2 bits and the right half 32 bits.

Kn is constructed from the key as shown on the right side of FIG. In FIG. 2, SI+.-.+S16 is 1 or 2. Further, reduced form transposition 2a is transposition excluding some of the inputs. In this case, 8 bits out of 56 bits of input are removed, resulting in 48 bits of output. Reduced form transposition is an irreversible transformation, and it is not possible to completely restore the input from the output. This makes key estimation more difficult.

Next, the function fK(R) in FIG. 2 will be explained using FIG. 3.

In FIG. 3, in order to create the function fK(R), R is first subjected to an extended form transposition 3a. Extended transposition is a transposition that duplicates some of the inputs. In this case, 3
Of the 2-bit input, 16 bits appear redundantly at the output. Next, K composed of keys is added bit by bit to this output mod 2. The resulting 48 bits are divided into eight small blocks of 6 bits, and each 6 bit is divided into S, , S2 . -..., each converted to 4 bits by S8. If we consider the 6 bits as one character, kone can be thought of as a type of upper half. 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 transformation of equation (1) above is irreversible. In fact, since equation (1) can be transformed as follows, it can be seen that , Rn-+ can be calculated from Lr, , Rn.

Now, repeat the calculation of formula (1) 16 times, L, 6. R,
After finding 6, transpose it one last time to finish the encryption.

Next, decoding will be explained.

Decryption can be performed by performing almost the opposite operation of encryption.

Simply put, all you have to do is proceed from the bottom to the top in Figure 2. First, perform the inverse transposition of the last transposition of encryption, and use the following equation (2) to obtain R, .

Once Ln-1 is obtained and Ro and Lo are obtained, the original 64 bits can be obtained by performing the reverse transposition of the initial transposition for encryption.

So far, there is no known way to decipher DES ciphertext other than examining each key one by one. Now, suppose it takes 1 microsecond to check whether a key is the correct key. At this time, 256
It would take 2,283 years to find all the keys. Even if you are very lucky, it will take several hundred years.

[Problem to be solved by the invention]

As explained above, in the conventional example, in the case of high-definition video images such as high-definition, if an analog image signal is simply A/D converted and transmitted, it is difficult to secure a video signal band of 30 MHz or more, for example. if you did this,
According to the sampling theorem, sampling must be performed at a rate of at least 60 MHz, 74.25 MHz, 8
When converting bits into A/D, the transmission rate is 74.25 (
MHz) X8 (bit) = 594 (Mbit
/s). Therefore, even if the amount of information is compressed to 115 to save transmission capacity, it will be approximately 120 (Mbit
/s). Encrypting and transmitting such a huge amount of information requires high-speed processing by the encryption unit.

The problem was that it was extremely difficult in terms of hardware size and cost.

This invention was made in order to solve the above-mentioned problems. It is possible to easily maintain confidentiality even in an extremely high-speed encoding transmission device, and since decryption is performed at a low speed, DES, etc. It is possible to use an LSI, etc. that complies with the encryption standards of The objective is to obtain a decryption device with high security performance that cannot be decrypted.

[Means to solve the problem]

Therefore, in the present invention, a storage means for storing a decoding table and reading a decoded value from an address determined by an encoding code, and a storage means for storing a decoding table and reading a decoded value from an address determined by an encoding code, and This object is achieved by a decryption device comprising: a decryption device that decrypts the code, restores the encrypted decryption table, and transfers the decryption table to the storage device. .

(Operation) The decoding device according to the present invention stores a decoding table in a storage means, reads a decoded value from an address determined by an encoding code, and loads a pre-encrypted decoding table into the storage means. At this time, the decryption and transfer means decodes the code, restores the encrypted decryption table, and transfers it to the storage means.

(Example〕 Hereinafter, one embodiment of the present invention will be described based on the drawings.

In this embodiment, a known prior value predictive coding method (hereinafter referred to as DPC) is used.
M) will be explained using an example.

FIG. 1 is a block diagram of an encoding apparatus according to an embodiment of the present invention. In FIG. 1 of the drawings, A is a storage means, and R is a storage means.
AM (decoding table) 3 is a means for storing the decoding table and reading the decoded value from the address determined by the encoded code. B is a restoration/transfer means, which decrypts the encryption when loading a pre-encrypted decryption table to the storage means A (details will be described later), restores the encrypted decryption table, and transfers it to the storage means A. It is a means to do so. 1 is a terminal to which the transmitted DPCM code Yi is input, 2 is an output terminal, and RAM 3, which constitutes a decoding table, receives the DPCM code Yi at its address input
and predicted value Xi (described later) are input. Reference numeral 5 represents a decryptor (described later), and reference numeral 6 represents an external storage device that stores a decryption table that has been encrypted in advance.

Next, the operation of this embodiment will be explained using FIG.

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

When the RAM 3 receives the above-mentioned DPCM code Yi and predicted value Xi, it outputs the corresponding decoded value in the rotated table to the output terminal 2 at the memory access time. RAM
The decoded value output from 3 is also applied to a D-type flip-flop 4. The output of the D-type flip-flop 4 is applied to the RAM 3 as the predicted value Xi.

Here, for example, the DPCM code Yi is 4 bits, RAM3
The decoded value outputted by the 8-bit, D-type flip-flop 4
Assuming that the predicted value Xi outputted by is 8 bits, the capacity of the RAM 3 is 4 x s bits, for a total of 32 bits. Now, if we use an LSI that decrypts the code at IMbit/second, the code can be decrypted in 0.032 seconds.

Furthermore, since the input data Yi is not encrypted, it can be decrypted as quickly as before. The decryption key can be easily changed by using a ROM cart or magnetic card as the storage device, mailing the decryption table to the recipient, and separately conveying the decryption key information.

This embodiment has been explained by taking previous value predictive encoding as an example, but it is a device that stores a decoding table in a storage device, transfers it to a decoding RAM, and performs decoding. Instead, encryption can be easily performed using other encoding methods such as hector quantization.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to easily maintain confidentiality even in extremely high-speed encoding and transmission equipment, and decryption is performed at low speed, so LSI etc. can be used, and encryption can be performed at a small size and low cost.

Furthermore, since the decoding table is encrypted, the transmitted code cannot be decoded unless the code is completely deciphered, making it possible to realize a transmission device with high security performance.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an encoding device that is an embodiment of the present invention, Fig. 2 is a flowchart showing conventional encryption, and Fig. 3 is a
It is a diagram showing a function that is the center of encryption in the figure. A -------Storage means B...Restore transfer means 1.7-...Terminal 3...RAM 4--D F/F 5... ...-Code decoder 6...External storage device

Claims (1)

[Scope of Claims] Storage means for storing a decoding table and reading a decoded value from an address determined by an encoding code; 1. A decryption device comprising: a restoration transfer means for decrypting a code, restoring the encrypted decryption table and transferring it to the storage means.