Task 011: .ACCDB File Format

The .ACCDB file format is a proprietary database file format used by Microsoft Access, introduced with Access 2007. It is an evolution of the earlier .MDB format, designed to support advanced features such as multivalued fields, data macros, and attachment data types. Below, I address the tasks as requested, with the caveat that the .ACCDB format is proprietary, and Microsoft has not released a public specification. Therefore, direct low-level manipulation of the file structure is complex and typically relies on high-level interfaces like ODBC or OLEDB. The solutions provided use these standard interfaces to interact with .ACCDB files.

1. Properties of the .ACCDB File Format Intrinsic to Its File System

Based on available information, the intrinsic properties of the .ACCDB file format related to its file system structure include:

• File Extension: .accdb
• Magic Number: Contains the string "Standard ACE DB" at the beginning of the file, identifying it as an Access database using the Access Connectivity Engine (ACE).
• Page Size: Fixed page size of 4096 bytes, used for structuring data within the file.
• Version/Compatibility Indicator: Located at offset 0x14 in the file, this byte indicates compatibility (e.g., 0x02 for Access 2007/2010, 0x05 for databases using newer features like large integer data types in Access 2016). This reflects compatibility rather than the exact ACE engine version.
• File Size Limit: Maximum file size of 2 gigabytes, influenced by the ability to store attachments and binary large objects (BLOBs) efficiently.
• Encryption Support: Supports enhanced encryption compared to .MDB, though specific algorithms are proprietary and managed via Access or ODBC settings.
• Lock File Association: When an .ACCDB file is opened, a temporary .laccdb lock file is created in the same directory to manage concurrent access and prevent accidental edits.
• Structured Storage: Binary format with a structured, symbolic organization, storing tables, queries, forms, reports, macros, and modules. It uses XML-based structures internally for some components, unlike the .MDB format.

These properties focus on the file system and structural aspects of .ACCDB files. Other features like multivalued fields or SharePoint integration are database-level functionalities, not intrinsic to the file system itself.

2. Python Class for .ACCDB File Handling

Python does not have built-in low-level access to .ACCDB file structures due to their proprietary nature. The pyodbc library, which interfaces with ODBC drivers, is used to interact with .ACCDB files. The following class opens an .ACCDB file, reads its properties, and prints them. Writing is limited to updating database metadata where applicable.

import pyodbc
import os
import binascii

class ACCDBFileHandler:
    def __init__(self, file_path):
        self.file_path = file_path
        self.connection = None
        self.properties = {}

    def open_file(self):
        try:
            # Use Microsoft Access Driver
            conn_str = f"Driver={{Microsoft Access Driver (*.mdb, *.accdb)}};DBQ={self.file_path};"
            self.connection = pyodbc.connect(conn_str)
            self._read_file_properties()
        except pyodbc.Error as e:
            print(f"Error opening .ACCDB file: {e}")
            return False
        return True

    def _read_file_properties(self):
        try:
            # Read file system properties
            self.properties['file_extension'] = os.path.splitext(self.file_path)[1].lower()
            self.properties['file_size'] = os.path.getsize(self.file_path)
            
            # Read magic number and version indicator
            with open(self.file_path, 'rb') as f:
                # Read first 20 bytes for magic number
                header = f.read(20)
                self.properties['magic_number'] = header[4:16].decode('ascii', errors='ignore')
                # Read version/compatibility at offset 0x14
                f.seek(20)
                version_byte = f.read(1)
                self.properties['version_indicator'] = int.from_bytes(version_byte, byteorder='little')
            
            # Check for lock file
            lock_file = os.path.splitext(self.file_path)[0] + '.laccdb'
            self.properties['lock_file_exists'] = os.path.exists(lock_file)
            
            # Page size (hardcoded as per documentation)
            self.properties['page_size'] = 4096
            
            # Encryption status (basic check via connection properties)
            if self.connection:
                cursor = self.connection.cursor()
                self.properties['encrypted'] = 'Unknown'  # ODBC may not expose encryption details
        except Exception as e:
            print(f"Error reading properties: {e}")

    def read_properties(self):
        return self.properties

    def write_properties(self, new_properties):
        # Limited write capability; .ACCDB metadata changes typically require Access
        print("Writing properties is limited. Use Microsoft Access for metadata modifications.")
        # Example: Could update database properties via SQL if supported
        try:
            if self.connection and 'database_property' in new_properties:
                cursor = self.connection.cursor()
                cursor.execute(f"ALTER DATABASE SET {new_properties['database_property']}")
                self.connection.commit()
                print("Database property updated (if supported).")
        except pyodbc.Error as e:
            print(f"Error writing properties: {e}")

    def print_properties(self):
        for key, value in self.properties.items():
            print(f"{key}: {value}")

    def close(self):
        if self.connection:
            self.connection.close()

# Example usage
if __name__ == "__main__":
    accdb_file = "sample.accdb"
    handler = ACCDBFileHandler(accdb_file)
    if handler.open_file():
        handler.print_properties()
        handler.close()

Notes:

• Requires the Microsoft Access Database Engine (ACE) driver installed.
• The write_properties method is limited because low-level metadata changes are proprietary and typically managed by Access.
• The magic number and version indicator are read directly from the file header, but other properties like encryption details may require Access-specific tools.

3. Java Class for .ACCDB File Handling

Java uses the JDBC-ODBC bridge or a third-party library like UCanAccess to interact with .ACCDB files. Below is a Java class using UCanAccess (a pure Java library) to avoid dependency on the ODBC driver, which is deprecated.

import net.ucanaccess.jdbc.UcanaccessDriver;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.io.File;
import java.io.RandomAccessFile;
import java.util.HashMap;
import java.util.Map;

public class ACCDBFileHandler {
    private String filePath;
    private Connection connection;
    private Map<String, Object> properties;

    public ACCDBFileHandler(String filePath) {
        this.filePath = filePath;
        this.properties = new HashMap<>();
    }

    public boolean openFile() {
        try {
            String connStr = "jdbc:ucanaccess://" + filePath;
            connection = DriverManager.getConnection(connStr);
            readFileProperties();
            return true;
        } catch (SQLException e) {
            System.err.println("Error opening .ACCDB file: " + e.getMessage());
            return false;
        }
    }

    private void readFileProperties() {
        try {
            File file = new File(filePath);
            properties.put("file_extension", filePath.substring(filePath.lastIndexOf(".")).toLowerCase());
            properties.put("file_size", file.length());

            // Read magic number and version indicator
            try (RandomAccessFile raf = new RandomAccessFile(file, "r")) {
                byte[] header = new byte[20];
                raf.read(header, 0, 20);
                properties.put("magic_number", new String(header, 4, 12, "ASCII"));
                raf.seek(20);
                byte versionByte = raf.readByte();
                properties.put("version_indicator", Byte.toUnsignedInt(versionByte));
            }

            // Check for lock file
            String lockFilePath = filePath.substring(0, filePath.lastIndexOf(".")) + ".laccdb";
            properties.put("lock_file_exists", new File(lockFilePath).exists());

            // Page size
            properties.put("page_size", 4096);

            // Encryption status (limited by UCanAccess)
            properties.put("encrypted", "Unknown");
        } catch (Exception e) {
            System.err.println("Error reading properties: " + e.getMessage());
        }
    }

    public Map<String, Object> readProperties() {
        return properties;
    }

    public void writeProperties(Map<String, Object> newProperties) {
        System.out.println("Writing properties is limited. Use Microsoft Access for metadata modifications.");
        // Example: Could attempt to set database properties via SQL
        try {
            if (connection != null && newProperties.containsKey("database_property")) {
                var stmt = connection.createStatement();
                stmt.execute("ALTER DATABASE SET " + newProperties.get("database_property"));
                System.out.println("Database property updated (if supported).");
            }
        } catch (SQLException e) {
            System.err.println("Error writing properties: " + e.getMessage());
        }
    }

    public void printProperties() {
        properties.forEach((key, value) -> System.out.println(key + ": " + value));
    }

    public void close() {
        try {
            if (connection != null) {
                connection.close();
            }
        } catch (SQLException e) {
            System.err.println("Error closing connection: " + e.getMessage());
        }
    }

    public static void main(String[] args) {
        ACCDBFileHandler handler = new ACCDBFileHandler("sample.accdb");
        if (handler.openFile()) {
            handler.printProperties();
            handler.close();
        }
    }
}

Notes:

• Requires the UCanAccess library (available via Maven or direct download).
• The writeProperties method is limited due to proprietary constraints.
• Direct file access is used for header properties like the magic number.

4. JavaScript Class for .ACCDB File Handling

JavaScript typically runs in environments (e.g., Node.js) that lack direct support for .ACCDB files. The node-adodb package can be used to interface with .ACCDB files via ADODB on Windows. Below is a class implementation:

const ADODB = require('node-adodb');
const fs = require('fs');

class ACCDBFileHandler {
    constructor(filePath) {
        this.filePath = filePath;
        this.connection = null;
        this.properties = {};
    }

    async openFile() {
        try {
            this.connection = ADODB.open(`Provider=Microsoft.ACE.OLEDB.12.0;Data Source=${this.filePath};`);
            await this.readFileProperties();
            return true;
        } catch (error) {
            console.error(`Error opening .ACCDB file: ${error.message}`);
            return false;
        }
    }

    async readFileProperties() {
        try {
            // File system properties
            const stats = fs.statSync(this.filePath);
            this.properties.file_extension = this.filePath.split('.').pop().toLowerCase();
            this.properties.file_size = stats.size;

            // Read magic number and version indicator
            const buffer = Buffer.alloc(21);
            const fd = fs.openSync(this.filePath, 'r');
            fs.readSync(fd, buffer, 0, 21, 0);
            fs.closeSync(fd);
            this.properties.magic_number = buffer.toString('ascii', 4, 16);
            this.properties.version_indicator = buffer.readUInt8(20);

            // Check for lock file
            const lockFile = this.filePath.replace('.accdb', '.laccdb');
            this.properties.lock_file_exists = fs.existsSync(lockFile);

            // Page size
            this.properties.page_size = 4096;

            // Encryption status
            this.properties.encrypted = 'Unknown';
        } catch (error) {
            console.error(`Error reading properties: ${error.message}`);
        }
    }

    getProperties() {
        return this.properties;
    }

    async writeProperties(newProperties) {
        console.log('Writing properties is limited. Use Microsoft Access for metadata modifications.');
        // Example: Attempt to update database properties
        try {
            if (this.connection && newProperties.database_property) {
                await this.connection.execute(`ALTER DATABASE SET ${newProperties.database_property}`);
                console.log('Database property updated (if supported).');
            }
        } catch (error) {
            console.error(`Error writing properties: ${error.message}`);
        }
    }

    printProperties() {
        for (const [key, value] of Object.entries(this.properties)) {
            console.log(`${key}: ${value}`);
        }
    }

    async close() {
        this.connection = null; // ADODB handles connection closure internally
    }
}

// Example usage
(async () => {
    const handler = new ACCDBFileHandler('sample.accdb');
    if (await handler.openFile()) {
        handler.printProperties();
        await handler.close();
    }
})();

Notes:

• Requires node-adodb and the Microsoft ACE OLEDB provider installed on Windows.
• Writing is limited to database-level changes via SQL, if supported.
• File system properties are read using Node.js fs module.

5. C Class for .ACCDB File Handling

C does not have a standard library for .ACCDB files, so we use ODBC via the Windows API. The following is a C implementation (Windows-specific):

#include <stdio.h>
#include <windows.h>
#include <sql.h>
#include <sqlext.h>
#include <string.h>

typedef struct {
    char file_extension[10];
    long long file_size;
    char magic_number[13];
    int version_indicator;
    int lock_file_exists;
    int page_size;
    char encrypted[20];
} ACCDBProperties;

typedef struct {
    char* file_path;
    SQLHENV env;
    SQLHDBC conn;
    ACCDBProperties properties;
} ACCDBFileHandler;

int init_handler(ACCDBFileHandler* handler, const char* file_path) {
    handler->file_path = strdup(file_path);
    handler->env = NULL;
    handler->conn = NULL;
    return 1;
}

int open_file(ACCDBFileHandler* handler) {
    SQLRETURN ret;
    SQLHSTMT stmt;

    ret = SQLAllocHandle(SQL_HANDLE_ENV, SQL_NULL_HANDLE, &handler->env);
    if (!SQL_SUCCEEDED(ret)) return 0;

    ret = SQLSetEnvAttr(handler->env, SQL_ATTR_ODBC_VERSION, (void*)SQL_OV_ODBC3, 0);
    if (!SQL_SUCCEEDED(ret)) return 0;

    ret = SQLAllocHandle(SQL_HANDLE_DBC, handler->env, &handler->conn);
    if (!SQL_SUCCEEDED(ret)) return 0;

    char conn_str[256];
    snprintf(conn_str, sizeof(conn_str), "Driver={Microsoft Access Driver (*.mdb, *.accdb)};DBQ=%s;", handler->file_path);
    ret = SQLDriverConnect(handler->conn, NULL, (SQLCHAR*)conn_str, SQL_NTS, NULL, 0, NULL, SQL_DRIVER_NOPROMPT);
    if (!SQL_SUCCEEDED(ret)) {
        printf("Error opening .ACCDB file\n");
        return 0;
    }

    read_file_properties(handler);
    return 1;
}

void read_file_properties(ACCDBFileHandler* handler) {
    // File extension
    const char* ext = strrchr(handler->file_path, '.');
    strncpy(handler->properties.file_extension, ext ? ext : ".accdb", sizeof(handler->properties.file_extension));

    // File size
    FILE* file = fopen(handler->file_path, "rb");
    if (file) {
        fseek(file, 0, SEEK_END);
        handler->properties.file_size = ftell(file);
        rewind(file);

        // Magic number and version indicator
        char buffer[21];
        fread(buffer, 1, 20, file);
        buffer[20] = '\0';
        strncpy(handler->properties.magic_number, buffer + 4, 12);
        handler->properties.magic_number[12] = '\0';
        fseek(file, 20, SEEK_SET);
        handler->properties.version_indicator = fgetc(file);
        fclose(file);
    }

    // Lock file
    char lock_file[256];
    snprintf(lock_file, sizeof(lock_file), "%.*s.laccdb", (int)(strlen(handler->file_path) - 6), handler->file_path);
    handler->properties.lock_file_exists = access(lock_file, F_OK) == 0;

    // Page size
    handler->properties.page_size = 4096;

    // Encryption
    strcpy(handler->properties.encrypted, "Unknown");
}

void write_properties(ACCDBFileHandler* handler, const char* property_name, const char* value) {
    printf("Writing properties is limited. Use Microsoft Access for metadata modifications.\n");
    // Example: SQL-based property update (limited support)
    if (handler->conn && property_name) {
        SQLHSTMT stmt;
        SQLAllocHandle(SQL_HANDLE_STMT, handler->conn, &stmt);
        char sql[256];
        snprintf(sql, sizeof(sql), "ALTER DATABASE SET %s", value);
        SQLRETURN ret = SQLExecDirect(stmt, (SQLCHAR*)sql, SQL_NTS);
        if (SQL_SUCCEEDED(ret)) {
            printf("Database property updated (if supported).\n");
        } else {
            printf("Error writing properties.\n");
        }
        SQLFreeHandle(SQL_HANDLE_STMT, stmt);
    }
}

void print_properties(ACCDBFileHandler* handler) {
    printf("file_extension: %s\n", handler->properties.file_extension);
    printf("file_size: %lld\n", handler->properties.file_size);
    printf("magic_number: %s\n", handler->properties.magic_number);
    printf("version_indicator: %d\n", handler->properties.version_indicator);
    printf("lock_file_exists: %d\n", handler->properties.lock_file_exists);
    printf("page_size: %d\n", handler->properties.page_size);
    printf("encrypted: %s\n", handler->properties.encrypted);
}

void close_handler(ACCDBFileHandler* handler) {
    if (handler->conn) SQLDisconnect(handler->conn);
    if (handler->conn) SQLFreeHandle(SQL_HANDLE_DBC, handler->conn);
    if (handler->env) SQLFreeHandle(SQL_HANDLE_ENV, handler->env);
    free(handler->file_path);
}

int main() {
    ACCDBFileHandler handler;
    init_handler(&handler, "sample.accdb");
    if (open_file(&handler)) {
        print_properties(&handler);
        close_handler(&handler);
    }
    return 0;
}

Notes:

• Requires the Microsoft Access Database Engine and ODBC drivers.
• Writing is limited due to proprietary restrictions.
• Uses Windows-specific ODBC APIs for database access.

General Notes and Limitations

• Proprietary Format: The .ACCDB format lacks a public specification, so low-level manipulation (e.g., direct binary parsing) is impractical without reverse-engineering efforts, which are beyond the scope of this response. The provided implementations rely on ODBC or equivalent interfaces.
• Dependencies: All implementations require the Microsoft Access Database Engine or equivalent drivers (e.g., ACE OLEDB) installed on the system.
• Writing Limitations: Modifying file system-level properties (e.g., magic number, page size) is not feasible without risking file corruption. Database-level metadata changes are possible but limited by the interfaces used.
• Cross-Platform: The Python, Java, and JavaScript solutions can work cross-platform with appropriate drivers, but the C solution is Windows-specific due to ODBC dependencies.
• Error Handling: Each implementation includes basic error handling, but real-world applications should include more robust checks.

If you need further customization or have a specific .ACCDB file to test, please provide additional details. For pricing or subscription-related questions about Microsoft Access, refer to official Microsoft resources, as I lack specific pricing information.

1. List of Properties Intrinsic to the .ACCDB File Format

Based on the file format specifications for .ACCDB (which uses the ACE database engine, an extension of Jet4), the following properties are stored in the database header (first page of the file, page 0, size 4096 bytes). These are the key intrinsic properties extracted from reverse-engineered documentation. The header includes a magic number and format ID for validation. Part of the header (starting at offset 0x18 for approximately 128 bytes in ACE/Jet4) is encrypted with RC4 using the key 0x6b39dac7 (as a 4-byte array: [0x6b, 0x39, 0xda, 0xc7]). The properties below are within or after this encrypted section and require decryption to read accurately. Offsets are in hexadecimal, sizes in bytes, and all multi-byte values are little-endian.

• Magic Number: Offset 0x00, Size 4, Type: bytes, Meaning: Fixed value 0x00010000 to identify the file as a Jet/ACE database.
• Format ID String: Offset 0x04, Size 20, Type: string (ASCII with nulls), Meaning: "Standard ACE DB\0\0\0\0\0" to identify ACE format (.ACCDB).
• Version Byte: Offset 0x14, Size 1, Type: byte, Meaning: ACE engine version (e.g., 0x02 for Access 2007, 0x05 for Access 2016 with advanced features).
• Code Page: Offset 0x3C, Size 2, Type: unsigned short, Meaning: Default database code page (e.g., 1252 for Western European).
• Database Key: Offset 0x3E, Size 4, Type: unsigned int, Meaning: Key used for encryption/decryption operations in the database.
• Password (Raw): Offset 0x42, Size 40, Type: bytes, Meaning: Raw encrypted/obfuscated database password (further masked by creation date; full decoding requires deriving mask from creation date).
• Sort Order: Offset 0x6E, Size 4, Type: unsigned int, Meaning: Default text collating sort order (e.g., 1033 for General).
• Creation Date: Offset 0x72, Size 8, Type: double (IEEE 754 floating-point), Meaning: Database creation timestamp (days since 1899-12-30).

Note: The page size is fixed at 4096 bytes for .ACCDB and is not stored as a variable property. Full password decoding is not implemented in the classes below as the exact mask derivation algorithm from the creation date is not publicly specified in available sources; the raw bytes are read/written instead.

2. Python Class

import struct

class AccdbHeader:
    def __init__(self, filename):
        self.filename = filename
        self.header = None
        self.properties = {}
        self.key = bytes([0x6b, 0x39, 0xda, 0xc7])  # RC4 key 0x6b39dac7

    def rc4(self, data):
        S = list(range(256))
        j = 0
        key_len = len(self.key)
        for i in range(256):
            j = (j + S[i] + self.key[i % key_len]) % 256
            S[i], S[j] = S[j], S[i]
        i = j = 0
        out = []
        for byte in data:
            i = (i + 1) % 256
            j = (j + S[i]) % 256
            S[i], S[j] = S[j], S[i]
            k = S[(S[i] + S[j]) % 256]
            out.append(byte ^ k)
        return bytes(out)

    def open_and_read(self):
        with open(self.filename, 'rb') as f:
            self.header = f.read(4096)  # Read first page
        if self.header[0:4] != b'\x00\x01\x00\x00' or self.header[4:24] != b'Standard ACE DB\x00\x00\x00\x00\x00':
            raise ValueError("Not a valid .ACCDB file")
        # Decrypt section starting at 0x18 (decrypt 256 bytes for safety)
        encrypted = self.header[0x18:0x18 + 256]
        decrypted = self.rc4(encrypted)
        decrypted_header = self.header[:0x18] + decrypted + self.header[0x18 + 256:]
        # Extract properties
        self.properties['Magic Number'] = decrypted_header[0x00:0x04]
        self.properties['Format ID String'] = decrypted_header[0x04:0x18].decode('ascii', errors='ignore').rstrip('\x00')
        self.properties['Version Byte'] = decrypted_header[0x14]
        self.properties['Code Page'] = struct.unpack('<H', decrypted_header[0x3C:0x3E])[0]
        self.properties['Database Key'] = struct.unpack('<I', decrypted_header[0x3E:0x42])[0]
        self.properties['Password (Raw)'] = decrypted_header[0x42:0x6A]
        self.properties['Sort Order'] = struct.unpack('<I', decrypted_header[0x6E:0x72])[0]
        self.properties['Creation Date'] = struct.unpack('<d', decrypted_header[0x72:0x7A])[0]
        return self.properties

    def write(self, new_properties):
        if self.header is None:
            raise ValueError("Must read file first")
        # Create mutable header
        mutable_header = bytearray(self.header)
        # Encrypt section for writing back
        decrypted = mutable_header[:0x18] + self.rc4(mutable_header[0x18:0x18 + 256]) + mutable_header[0x18 + 256:]
        # Update properties in decrypted
        if 'Code Page' in new_properties:
            struct.pack_into('<H', decrypted, 0x3C, new_properties['Code Page'])
        if 'Database Key' in new_properties:
            struct.pack_into('<I', decrypted, 0x3E, new_properties['Database Key'])
        if 'Password (Raw)' in new_properties:
            decrypted[0x42:0x6A] = new_properties['Password (Raw)']
        if 'Sort Order' in new_properties:
            struct.pack_into('<I', decrypted, 0x6E, new_properties['Sort Order'])
        if 'Creation Date' in new_properties:
            struct.pack_into('<d', decrypted, 0x72, new_properties['Creation Date'])
        # Re-encrypt the section
        re_encrypted = self.rc4(decrypted[0x18:0x18 + 256])
        mutable_header[0x18:0x18 + 256] = re_encrypted
        # Write back to file (append rest of file if larger)
        with open(self.filename, 'rb+') as f:
            f.write(mutable_header)

3. Java Class

import java.io.RandomAccessFile;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.util.HashMap;
import java.util.Map;

public class AccdbHeader {
    private String filename;
    private byte[] header;
    private Map<String, Object> properties = new HashMap<>();
    private byte[] key = {(byte)0x6b, (byte)0x39, (byte)0xda, (byte)0xc7}; // RC4 key 0x6b39dac7

    public AccdbHeader(String filename) {
        this.filename = filename;
    }

    private byte[] rc4(byte[] data) {
        int[] S = new int[256];
        for (int i = 0; i < 256; i++) S[i] = i;
        int j = 0;
        int keyLen = key.length;
        for (int i = 0; i < 256; i++) {
            j = (j + S[i] + (key[i % keyLen] & 0xFF)) % 256;
            int temp = S[i];
            S[i] = S[j];
            S[j] = temp;
        }
        int i = 0;
        j = 0;
        byte[] out = new byte[data.length];
        for (int k = 0; k < data.length; k++) {
            i = (i + 1) % 256;
            j = (j + S[i]) % 256;
            int temp = S[i];
            S[i] = S[j];
            S[j] = temp;
            int keystream = S[(S[i] + S[j]) % 256];
            out[k] = (byte) (data[k] ^ keystream);
        }
        return out;
    }

    public Map<String, Object> openAndRead() throws IOException {
        try (RandomAccessFile file = new RandomAccessFile(filename, "r")) {
            header = new byte[4096];
            file.readFully(header);
        }
        ByteBuffer bb = ByteBuffer.wrap(header).order(ByteOrder.LITTLE_ENDIAN);
        if (bb.getInt(0) != 0x00010000 || !new String(header, 4, 20).startsWith("Standard ACE DB")) {
            throw new IOException("Not a valid .ACCDB file");
        }
        // Decrypt 256 bytes from 0x18
        byte[] encrypted = new byte[256];
        System.arraycopy(header, 0x18, encrypted, 0, 256);
        byte[] decrypted = rc4(encrypted);
        byte[] decryptedHeader = new byte[4096];
        System.arraycopy(header, 0, decryptedHeader, 0, 0x18);
        System.arraycopy(decrypted, 0, decryptedHeader, 0x18, 256);
        System.arraycopy(header, 0x18 + 256, decryptedHeader, 0x18 + 256, 4096 - (0x18 + 256));
        ByteBuffer dbb = ByteBuffer.wrap(decryptedHeader).order(ByteOrder.LITTLE_ENDIAN);
        properties.put("Magic Number", new byte[]{dbb.get(0), dbb.get(1), dbb.get(2), dbb.get(3)});
        properties.put("Format ID String", new String(decryptedHeader, 0x04, 20).trim());
        properties.put("Version Byte", dbb.get(0x14));
        properties.put("Code Page", dbb.getShort(0x3C) & 0xFFFF);
        properties.put("Database Key", dbb.getInt(0x3E) & 0xFFFFFFFFL);
        byte[] password = new byte[40];
        dbb.position(0x42);
        dbb.get(password);
        properties.put("Password (Raw)", password);
        properties.put("Sort Order", dbb.getInt(0x6E) & 0xFFFFFFFFL);
        properties.put("Creation Date", dbb.getDouble(0x72));
        return properties;
    }

    public void write(Map<String, Object> newProperties) throws IOException {
        if (header == null) {
            throw new IOException("Must read file first");
        }
        // Decrypt for update
        byte[] encrypted = new byte[256];
        System.arraycopy(header, 0x18, encrypted, 0, 256);
        byte[] decrypted = rc4(encrypted);
        byte[] mutableHeader = new byte[4096];
        System.arraycopy(header, 0, mutableHeader, 0, 0x18);
        System.arraycopy(decrypted, 0, mutableHeader, 0x18, 256);
        System.arraycopy(header, 0x18 + 256, mutableHeader, 0x18 + 256, 4096 - (0x18 + 256));
        ByteBuffer bb = ByteBuffer.wrap(mutableHeader).order(ByteOrder.LITTLE_ENDIAN);
        if (newProperties.containsKey("Code Page")) {
            bb.putShort(0x3C, ((Number) newProperties.get("Code Page")).shortValue());
        }
        if (newProperties.containsKey("Database Key")) {
            bb.putInt(0x3E, ((Number) newProperties.get("Database Key")).intValue());
        }
        if (newProperties.containsKey("Password (Raw)")) {
            bb.position(0x42);
            bb.put((byte[]) newProperties.get("Password (Raw)"));
        }
        if (newProperties.containsKey("Sort Order")) {
            bb.putInt(0x6E, ((Number) newProperties.get("Sort Order")).intValue());
        }
        if (newProperties.containsKey("Creation Date")) {
            bb.putDouble(0x72, (Double) newProperties.get("Creation Date"));
        }
        // Re-encrypt
        byte[] toEncrypt = new byte[256];
        System.arraycopy(mutableHeader, 0x18, toEncrypt, 0, 256);
        byte[] reEncrypted = rc4(toEncrypt);
        System.arraycopy(reEncrypted, 0, mutableHeader, 0x18, 256);
        // Write back
        try (RandomAccessFile file = new RandomAccessFile(filename, "rw")) {
            file.write(mutableHeader);
        }
    }
}

4. JavaScript Class (Node.js)

const fs = require('fs');

class AccdbHeader {
    constructor(filename) {
        this.filename = filename;
        this.header = null;
        this.properties = {};
        this.key = Buffer.from([0x6b, 0x39, 0xda, 0xc7]); // RC4 key 0x6b39dac7
    }

    rc4(data) {
        let S = Array.from({length: 256}, (_, i) => i);
        let j = 0;
        const keyLen = this.key.length;
        for (let i = 0; i < 256; i++) {
            j = (j + S[i] + this.key[i % keyLen]) % 256;
            [S[i], S[j]] = [S[j], S[i]];
        }
        let i = 0;
        j = 0;
        const out = Buffer.alloc(data.length);
        for (let k = 0; k < data.length; k++) {
            i = (i + 1) % 256;
            j = (j + S[i]) % 256;
            [S[i], S[j]] = [S[j], S[i]];
            const keystream = S[(S[i] + S[j]) % 256];
            out[k] = data[k] ^ keystream;
        }
        return out;
    }

    openAndRead() {
        this.header = fs.readFileSync(this.filename, {encoding: null}).slice(0, 4096);
        const bb = this.header;
        if (bb.readUInt32LE(0) !== 0x00010000 || bb.toString('ascii', 4, 24).indexOf('Standard ACE DB') !== 0) {
            throw new Error('Not a valid .ACCDB file');
        }
        // Decrypt 256 bytes from 0x18
        const encrypted = bb.slice(0x18, 0x18 + 256);
        const decrypted = this.rc4(encrypted);
        const decryptedHeader = Buffer.alloc(4096);
        bb.copy(decryptedHeader, 0, 0, 0x18);
        decrypted.copy(decryptedHeader, 0x18);
        bb.copy(decryptedHeader, 0x18 + 256, 0x18 + 256);
        this.properties['Magic Number'] = decryptedHeader.slice(0x00, 0x04);
        this.properties['Format ID String'] = decryptedHeader.toString('ascii', 0x04, 0x18).replace(/\0/g, '');
        this.properties['Version Byte'] = decryptedHeader[0x14];
        this.properties['Code Page'] = decryptedHeader.readUInt16LE(0x3C);
        this.properties['Database Key'] = decryptedHeader.readUInt32LE(0x3E);
        this.properties['Password (Raw)'] = decryptedHeader.slice(0x42, 0x6A);
        this.properties['Sort Order'] = decryptedHeader.readUInt32LE(0x6E);
        this.properties['Creation Date'] = decryptedHeader.readDoubleLE(0x72);
        return this.properties;
    }

    write(newProperties) {
        if (!this.header) {
            throw new Error('Must read file first');
        }
        const mutableHeader = Buffer.from(this.header);
        // Decrypt for update
        const encrypted = mutableHeader.slice(0x18, 0x18 + 256);
        let decrypted = this.rc4(encrypted);
        const mutableDecrypted = Buffer.alloc(4096);
        mutableHeader.copy(mutableDecrypted, 0, 0, 0x18);
        decrypted.copy(mutableDecrypted, 0x18);
        mutableHeader.copy(mutableDecrypted, 0x18 + 256, 0x18 + 256);
        if ('Code Page' in newProperties) {
            mutableDecrypted.writeUInt16LE(newProperties['Code Page'], 0x3C);
        }
        if ('Database Key' in newProperties) {
            mutableDecrypted.writeUInt32LE(newProperties['Database Key'], 0x3E);
        }
        if ('Password (Raw)' in newProperties) {
            newProperties['Password (Raw)'].copy(mutableDecrypted, 0x42);
        }
        if ('Sort Order' in newProperties) {
            mutableDecrypted.writeUInt32LE(newProperties['Sort Order'], 0x6E);
        }
        if ('Creation Date' in newProperties) {
            mutableDecrypted.writeDoubleLE(newProperties['Creation Date'], 0x72);
        }
        // Re-encrypt
        const toEncrypt = mutableDecrypted.slice(0x18, 0x18 + 256);
        const reEncrypted = this.rc4(toEncrypt);
        reEncrypted.copy(mutableHeader, 0x18);
        // Write back (overwrite first 4096 bytes)
        fs.writeFileSync(this.filename, mutableHeader.slice(0, 4096));
        // Note: If file larger, rest remains unchanged
    }
}

5. C Class (using struct for simplicity, assumes little-endian platform)

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>

// Simple RC4 implementation
void rc4(uint8_t *key, size_t key_len, uint8_t *data, size_t data_len) {
    uint8_t S[256];
    for (size_t i = 0; i < 256; i++) S[i] = i;
    size_t j = 0;
    for (size_t i = 0; i < 256; i++) {
        j = (j + S[i] + key[i % key_len]) % 256;
        uint8_t temp = S[i];
        S[i] = S[j];
        S[j] = temp;
    }
    size_t i = 0;
    j = 0;
    for (size_t k = 0; k < data_len; k++) {
        i = (i + 1) % 256;
        j = (j + S[i]) % 256;
        uint8_t temp = S[i];
        S[i] = S[j];
        S[j] = temp;
        uint8_t keystream = S[(S[i] + S[j]) % 256];
        data[k] ^= keystream;
    }
}

typedef struct {
    uint8_t magic[4];
    char format_id[20];
    uint8_t version;
    uint16_t code_page;
    uint32_t db_key;
    uint8_t password[40];
    uint32_t sort_order;
    double creation_date;
} AccdbProperties;

typedef struct {
    const char *filename;
    uint8_t *header;
    AccdbProperties props;
} AccdbHeader;

AccdbHeader *accdb_open(const char *filename) {
    AccdbHeader *obj = malloc(sizeof(AccdbHeader));
    obj->filename = filename;
    obj->header = malloc(4096);
    FILE *f = fopen(filename, "rb");
    if (!f || fread(obj->header, 4096, 1, f) != 1) {
        free(obj->header);
        free(obj);
        return NULL;
    }
    fclose(f);
    if (memcmp(obj->header, "\x00\x01\x00\x00", 4) != 0 || memcmp(obj->header + 4, "Standard ACE DB", 15) != 0) {
        free(obj->header);
        free(obj);
        return NULL;
    }
    // Decrypt 256 bytes from 0x18
    uint8_t key[] = {0x6b, 0x39, 0xda, 0xc7};
    uint8_t *encrypted = malloc(256);
    memcpy(encrypted, obj->header + 0x18, 256);
    rc4(key, 4, encrypted, 256);
    uint8_t *decrypted_header = malloc(4096);
    memcpy(decrypted_header, obj->header, 0x18);
    memcpy(decrypted_header + 0x18, encrypted, 256);
    memcpy(decrypted_header + 0x18 + 256, obj->header + 0x18 + 256, 4096 - (0x18 + 256));
    free(encrypted);
    // Extract properties (assuming little-endian)
    memcpy(obj->props.magic, decrypted_header + 0x00, 4);
    memcpy(obj->props.format_id, decrypted_header + 0x04, 20);
    obj->props.format_id[19] = '\0'; // Null-terminate
    obj->props.version = *(decrypted_header + 0x14);
    obj->props.code_page = *((uint16_t *)(decrypted_header + 0x3C));
    obj->props.db_key = *((uint32_t *)(decrypted_header + 0x3E));
    memcpy(obj->props.password, decrypted_header + 0x42, 40);
    obj->props.sort_order = *((uint32_t *)(decrypted_header + 0x6E));
    obj->props.creation_date = *((double *)(decrypted_header + 0x72));
    free(decrypted_header);
    return obj;
}

void accdb_write(AccdbHeader *obj, AccdbProperties *new_props) {
    if (!obj->header) return;
    // Decrypt for update
    uint8_t key[] = {0x6b, 0x39, 0xda, 0xc7};
    uint8_t *encrypted = malloc(256);
    memcpy(encrypted, obj->header + 0x18, 256);
    rc4(key, 4, encrypted, 256);
    uint8_t *mutable_decrypted = malloc(4096);
    memcpy(mutable_decrypted, obj->header, 0x18);
    memcpy(mutable_decrypted + 0x18, encrypted, 256);
    memcpy(mutable_decrypted + 0x18 + 256, obj->header + 0x18 + 256, 4096 - (0x18 + 256));
    free(encrypted);
    // Update
    *((uint16_t *)(mutable_decrypted + 0x3C)) = new_props->code_page;
    *((uint32_t *)(mutable_decrypted + 0x3E)) = new_props->db_key;
    memcpy(mutable_decrypted + 0x42, new_props->password, 40);
    *((uint32_t *)(mutable_decrypted + 0x6E)) = new_props->sort_order;
    *((double *)(mutable_decrypted + 0x72)) = new_props->creation_date;
    // Re-encrypt
    uint8_t *to_encrypt = malloc(256);
    memcpy(to_encrypt, mutable_decrypted + 0x18, 256);
    rc4(key, 4, to_encrypt, 256);
    memcpy(obj->header + 0x18, to_encrypt, 256);
    free(to_encrypt);
    free(mutable_decrypted);
    // Write back
    FILE *f = fopen(obj->filename, "r+b");
    if (f) {
        fwrite(obj->header, 4096, 1, f);
        fclose(f);
    }
}

void accdb_close(AccdbHeader *obj) {
    free(obj->header);
    free(obj);
}

// Example usage: AccdbHeader *h = accdb_open("file.accdb"); accdb_write(h, &new_props); accdb_close(h);