Some aviation geophysical exploration projects have a certain level of confidentiality, and the data obtained by the projects are confidential data and are also stored in the database of this system. Therefore, it is necessary to prevent confidential data from being stolen or deliberately destroyed, such as unauthorized extraction of confidential data from databases or eavesdropping on communication lines. For this kind of threat, the most effective solution is to encrypt data, convert readable confidential data into encrypted data, store and transmit it in encrypted format, and decrypt it when using it.

The confidentiality level of airborne geophysical prospecting is divided into three levels: confidential, secret and top secret. This system only encrypts confidential project data, confidential and secret project data are encrypted with 64-bit key, top-secret project data are encrypted with 128-bit key, and non-confidential project data are not encrypted. After the data entering the data collection library passes the correctness check, the system will automatically encrypt it according to the set project security level when filing and warehousing. Users can also encrypt or decrypt the data in the database through the encryption and decryption function. The same type of encrypted data and unencrypted data are stored in the same field of the same table in the database, but in the data encryption and decryption record table database (Table 3-8), the table code and field code of the encrypted database are recorded. When the user is authorized to access confidential data, the system will automatically decrypt the data according to the records in the table.

Table 3-8 Database Structure of Data Encryption and Decryption Record Table

I. Data encryption and decryption

According to the different types of keys, modern cryptography can be divided into two categories: symmetric encryption algorithm (secret key encryption) and asymmetric encryption algorithm (public key encryption). Symmetric key encryption system uses the same key for encryption and decryption, and both parties must obtain this key and keep it secret. The encryption key (public key) and decryption key (private key) used in asymmetric key encryption system are different.

Symmetric encryption algorithm is used to encrypt sensitive data and other information. The commonly used algorithms are DES (Data Encryption Standard), which is fast and suitable for encrypting a large amount of data. 3DES(Triple DES), based on DES, uses three different keys to encrypt a piece of data for three times, with higher strength; AES (Advanced Encryption Standard) is an advanced encryption standard with high speed and high security level. Common asymmetric encryption algorithms are: RSA invented by RSA Company is a public key algorithm, which supports variable-length keys, and the fast length of the file to be encrypted is also variable; Digital signature algorithm DSA(Digital Signature Algorithm) is a standard DSS (Digital Signature Standard).

The system uses AES and DES encryption algorithms to add or decrypt database data (Figure 3-4).

Figure 3-4 Database Data Encryption-decryption Process

AES encryption algorithm is a new key encryption standard published by National Institute of Standards and Technology (NIST) in June 2000, and a new advanced encryption standard (AES) specification was formulated on May 26th, 2002.

AES algorithm is based on permutation (rearranging data) and permutation (replacing one data unit with another), and uses several different methods to perform permutation and permutation operations. It is an iterative symmetric key block cipher, which can be encrypted and decrypted with 128, 192 and 256 bits, and with 128 bits (16 bytes). The number of bits of encrypted data returned by block cipher is the same as that of input data. Iterative encryption uses a circular structure in which input data is repeatedly permuted and replaced.

DES algorithm turns a 64-bit plaintext input block into a 64-bit ciphertext output block, and the key it uses is also 64 bits. First, DES reassembles the input 64-bit data block bit by bit, and divides the output into two parts, L0 and R0, each part is 32 bits long, and carries out replacement before and after (the 58th bit of the input is changed to 1 bit, the 50th bit is changed to the 2nd bit, and so on, and the last bit is the original 7th bit). Finally, L0 outputs the left 32 bits and R0 outputs the right 32 bits. According to this rule, after 16 iterations, L 16 and r 16 are obtained, which are used as inputs, and the ciphertext output is obtained by performing the reverse arrangement opposite to the initial arrangement.

Second, the log tracking

In order to effectively monitor the access of classified data in aviation geophysical exploration and ensure the security of classified data, this system has developed the tracking function of classified data access log. This function is similar to "video camera", which records the time, user, IP address and other information of accessing confidential data in the database in the log database table for investigation.

First, define the log tracking of confidential data, that is, which operations of users are tracked. The system provides the function of tracking users' queries, additions, modifications and deletions, and you can select one or more of them as required (Figure 3-5).

After the log tracking definition comes into effect, the system automatically tracks users, recording their login names, login and logout times (year/month/day, hour/minute/second), IP addresses of login computers, and queries, additions, modifications and deletions of database data by users. The system also provides the functions of logging, querying, printing and exporting Excel spreadsheet files, which is convenient for database administrators to use.

Figure 3-5 Database Log Tracking Settings

Thirdly, the security mechanism of data extraction.

Data extraction is one of the important contents of data service provided by aviation geophysical information system for researchers in the fields of geology and geophysics. Preventing unauthorized data extraction and ensuring data security are the prerequisites for the system to provide high-quality and efficient services.

Extracting data beyond authority is a problem in two aspects. First, users steal data without authorization, which is a system security problem. Second, authorize users to expand the scope of extracting data without authorization and "steal" more data. In order to solve this problem, this system adopts the following mechanism (Figure 3-6).

Figure 3-6 Database Data Extraction Security Mechanism Model

First of all, users (units or individuals who need data) apply for using data and fill in the approval form for using data. The table contains information such as application number, applicant, range of data used (latitude and longitude coordinates), approver, approval date and purpose of using data.

After the user's application is passed, he will sign a confidentiality agreement with the center for information use. The system administrator grants the user "data extraction authority", and sets the scope of data extraction and the validity period of data extraction authority according to the approved application.

During the validity period, users can extract the data within the set range. At the same time, the system automatically records the user data extraction log in the data extraction record table (recording the range of extracted data, data measurement scale, database table of data source, data extractor and extraction date, etc.). ) for future reference.