JPH06132953A - Telemetry ciphering device - Google Patents

Abstract

PURPOSE:To reduce the probability that the same bit patterns emerge in a period equivalent to a major frame by ciphering once the major frame telemetry data. CONSTITUTION:A 1st ciphering device 3a is provided together with a 1st timing circuit 2, a 2nd ciphering device 3b, and a 2nd timing circuit 4. The major frame telemetry data 6 is once ciphered before the final ciphering operation. Therefore the data 6 is converted into a random bit pattern by ciphering even if the data 6 does not timewisely change at all. Thus the data 6 is synthesized with the minor frame telemetry data 5 and formed into a telemetry format, and the probability that some regularity emerges in a major frame in a period equivalent to a major frame pulse.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a telemetry encryption device mounted on an artificial satellite.

[0002]

2. Description of the Related Art An artificial satellite is always equipped with a device called a telemetry encoder. This is the temperature, voltage, etc. of each part of the satellite and various equipment mounted on it.
It collects electrical and mechanical housekeeping data indicating current or operating conditions and converts it into a predetermined format, which is commonly referred to as telemetry data. This telemetry data is constantly transmitted to the ground, and by receiving and analyzing this telemetry data on the ground, it is possible to know the operating status of each part of the artificial satellite and the various equipment installed. it can.

This telemetry data usually has a major frame period of about several [S] identified by a major frame synchronization pattern. Further, this major frame is composed of a plurality of minor frames. Minor frames are identified by a minor frame synchronization pattern, but usually dozens of [m
It has a period from S] to several hundred [mS]. Most housekeeping data is 1 per 1 minor frame
The frame format of the telemetry data is designed to be sampled once.

However, depending on the type of housekeeping data, there are some that are not expected to change so rapidly in time, and some that are not important as data. In this case, the major frame period is used. Sampling the data is said to be sufficient. If such data is collectively included in the telemetry data only once in the major frame, the minor frame period is shortened, the utilization efficiency of the major frame and the minor frame is improved, and the time is also reduced. It is possible to change extremely rapidly, and to shorten the sampling period of extremely important housekeeping data.

In order to realize this, in general, one is provided at a fixed position of a minor frame and one is provided for a major frame.
Reserve a slot for data to be transmitted only once, 1
The transmission of the data is completed over a plurality of minor frames that form a major frame. The data transmitted in slots other than this slot is always transmitted once in one minor frame, but the data in this slot is transmitted only once in one major frame. The former data is called minor frame telemetry data, and the latter data is called major frame telemetry data.

On the other hand, in digital communication, a signal from an information source is generally converted into a binary numerical sequence consisting of "1" and "0", and a carrier signal is modulated by this binary signal, which is wirelessly or wired. It is sent to the transmission line and transmitted to the destination. Here, on any transmission line,
Interception by a third party is not impossible. Therefore, a so-called cryptographic communication system is constructed in which the information source data having confidentiality is encrypted on the transmitting side and the signal from the original information source is restored by decrypting the data on the receiving side at the destination.

As cryptographic communication systems, those based on various principles have been proposed and put into practical use, and one of the systems often used is called a secret key cryptosystem. In this secret key cryptosystem, a transposition method that replaces the order of information such as characters, and a substitution method that replaces information such as characters with other characters are used. Substitution is repeated. Operations such as character transposition and character replacement are uniquely determined by the algorithm itself and a numerical parameter called an encryption key that quantitatively defines the algorithm. It is a secret key cryptosystem. In this case, the information sent from the transmission source that is encrypted and sent to the transmission path cannot be decrypted by a third party who does not know the encryption key, and can only be decrypted by a legitimate receiving side who knows it. Become.

[0008] In particular, regarding telemetry data of artificial satellites, it is expected that interception by a third party will be extremely easy due to the nature of satellite communication such as broadcastability, and it is often necessary to perform encryption. In general, in order to maintain communication synchronization, the synchronization pattern inserted in the data stream is often not encrypted. Even in the above telemetry data, only the part excluding the synchronization pattern is encrypted. Become. However, it is usually sufficient to exclude only major frame sync patterns from encryption,
Even if the minor frame synchronization pattern is encrypted, the communication synchronization is sufficiently secured.

FIG. 2 is a block diagram of a conventional telemetry cipher device. In FIG. 2, reference numeral 2 is a first one for converting a minor frame telemetry data and a major frame telemetry data into a predetermined format.
Timing circuit, 3 is an encoder for encrypting the output of the first timing circuit, 4 is a second timing circuit for adding a synchronization pattern (major frame synchronization pulse) to the output of the encoder 3, and 5 is a minor Frame telemetry
Data, 6 is major frame telemetry data, and 7 is telemetry data.

Next, the operation will be described. The minor frame telemetry data of 5 and the major frame telemetry data of 6 are stored in the first timing circuit 2
After being converted into a predetermined format in (3), the data is encrypted by the encryption device (3), the major frame synchronization pattern is added in the second timing circuit (4), and the final telemetry data (7) is output.

[0011]

In the cryptographic communication system, a third party who illegally intercepts a signal on the transmission line uses an encryption key by some means from the ciphertext (encrypted information) intercepted on the transmission line. Try to estimate. A known example of this is a known plaintext attack in which a known plaintext is deliberately made to sneak into the plaintext (information before being encrypted), and the corresponding ciphertext is intercepted. Collecting various samples from regularity,
A method of analogizing the encryption key by cut-and-try is often used. A synchronization pattern is required to transmit data, but since the overhead for synchronizing these so-called communications is usually not encrypted, there is always some periodicity in the data intercepted on the transmission path. Because it appears.

Further, it is expected that the major frame telemetry data will not change so rapidly in time due to its nature and will have substantially the same value over a considerable period. However, in encryption by substitution or transposition, if the plaintext data is the same, the bit patterns appearing in the ciphertext will be very similar. Therefore, in this case, the major frame sync pattern (since the minor frame telemetry data of 5 in FIG. 2 includes the minor frame sync pattern, the minor frame sync pattern is assumed to be encrypted. Is not encrypted and appears periodically in the ciphertext, and major frame telemetry data that spans multiple minor frames has a bit pattern that is similar to each other and that corresponds to the major frame. Will appear in the ciphertext. For a third party who intercepts the ciphertext, this can be powerful information for analogizing the encryption key.

The present invention has been made in order to solve the above-mentioned problems. By pre-encrypting the major frame telemetry data, the major frame telemetry data is transmitted at the major frame cycle. The purpose is to prevent it from appearing in the ciphertext.

[0014]

An encryption device according to the present invention encrypts major frame telemetry data once in advance. This intermediate data is combined with minor frame telemetry data to create a predetermined major frame format, and a major frame synchronization pattern is added. By these operations, it is possible to prevent the major frame telemetry data from being converted into bit patterns similar to each other and appearing in the ciphertext at the cycle of the major frame.

[0015]

The ciphertext output from this cryptographic device has the periodicity shown by the major frame synchronization pattern, but the major frame telemetry data that does not change so rapidly with time is Since the bit patterns that are similar to each other do not appear in the cycle corresponding to the frame, a third party who intercepts this can reduce the number of samples for decryption obtained from the periodicity of the ciphertext.

[0016]

1 is a block diagram of a telemetry cipher device showing an embodiment of the present invention, in which 3a is a first cipher, 2 is a first timing circuit, 3b is a second cipher, 4 is a second timing circuit, 5 is minor frame telemetry data, 6 is major frame telemetry data, and 7 is telemetry data.

In the above embodiment, the major frame telemetry data is encrypted once before the final encryption. Therefore, even if the major frame telemetry data does not change at all at all, it is converted into a random bit pattern by this encryption. Therefore, minor frame telemetry
After being combined with the data to form a telemetry format, the probability that some regularity will appear in the major frame at the period corresponding to the major frame pulse is very small.

[0018]

In the above embodiment, since the major frame telemetry data is encrypted in advance, even if the major frame telemetry data does not change at all, it is the minor frame telemetry data. The probability that the same bit pattern will appear in a cycle corresponding to a major frame after it is combined with data and encrypted will be extremely small. Also,
Even if the cycle of the major frame telemetry data is detected, it is once encrypted, so that the possibility of decryption is extremely low.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a conventional example.

[Explanation of symbols]

 2 1st timing circuit 3a 1st encryption device 3b 2nd encryption device 4 2nd timing circuit 5 Minor frame telemetry data 6 Major frame telemetry data 7 Telemetry data

Claims (1)

[Claims] 1. A first cipher for encrypting major frame telemetry data, and a minor frame for receiving an output of the first cipher and externally input.
A first timing circuit for converting into a predetermined format in combination with telemetry data, a second encryption device for receiving and encrypting the output of the first timing circuit, and an output of the second encryption device. And a second timing circuit for receiving telemetry data and outputting the telemetry data to the outside by adding a major frame synchronization pattern to the telemetry cryptographic device.