Novel Data Idea

How data obfuscation works:

First, tool adds a class called Decryptor to the app, with:

• decrypt(string encrypted) that returns the decrypted string
• intDecrypt(string encrypted) that returns decrypted int

For strings

0. String original = "original string";
1. tool has method encrypt(string original) to return string "3ncrypt3d 5tr1ng"
2. change line into var = Decryptor.decrypt("3ncrypt3d 5tr1ng");
3. Basically .decrypt(string encrypted) performs the algorithm for decryption
4. At runtime .decrypt will be called and original = "original string" again

For ints

1. source code: int i = 3;
2. tool: intEncryptor(int i) returns string "3ncrypt3d 1nt"
3. source code modified: int i = Decyptor.intDecrypt("3ncrypt3d 1nt");
4. source code added method: Decyptor.intDecrypt(string encryptedInt) takes "3ncrypt3d 1nt" and returns 3

Somewhat novel data obfuscation idea (for strings only):

• 1.1 have multiple encryptors methods (encryptor1,2,3,...)

• 1.2 when encrypting, use a random encryptor

• 1.3 append the encryptor number onto the start of the encrypted string

• 1.4 so encryptor1 returns "13ncrypt3d 5tr1ng", encryptor2 returns "23ncrypt3d 5tr1ng"

• 1.5 base64 encode the encrypted string

• 4.1 Decryptor.decrypt first base 64 decodes to get encrypted string "23ncrypt3d 5tr1ng"

• 4.2 switches on the first character of encrypted string

• 4.3 the cases perform different types of decryption accordingly

Our tool

/**
In our tool
**/
public class DataEncryptor {
	private final int NUMBER_OF_ENCRYPTORS = 5;
	private static int encryptor = 0;

	public void toolEncrypt(Node n) { //it can take anything		
		/* TODO:
		Terran what are the possible Nodes that can be passed in for modification?
can make this random :)
		*/
		
			if(isString){
				//get the part to modify
				SomeType actualStringPart; //TODO the part that contains the actual string
				if(isParameter) {
					actualStringPart = ;
				} else if(isAssignment) {
					actualStringPart = ;
				}

				//find encryptor
				encryptor++;
				encryptor = encryptor % NUMBER_OF_ENCRYPTORS;
				
				//encrypt the string 
				string encryptedString = stringEncrypt(s, encryptor);
				
				//append encryptor
				string appendedString = encryptor+base64String; //append encryptor identifier to start

				//base 64 whole thing
				string base64String = Base64.getEncoder().encodeToString(encryptedString.getBytes(StandardCharsets.UTF_8));
				
				//do the modification
				actualStringPart = "Decryptor.decrypt(\"" + base64String + "\")"; //might need to import Decryptor or use fully qualified name
			} else if(isInt) {
				//get the part to modify
				SomeType actualIntPart; //TODO the part that contains the actual int
				if(isParameter) {
					actualStringPart = ;
				} else if(isAssignment) {
					actualStringPart = ;
				}
				
				string obfuscatedInt = ; //Sejal's number encryptor
				
				//do the modification
				actualIntPart = "Decryptor.intDecrypt(\"" + obfuscatedInt + "\")"; //might need to import 
			}
		}
	}

	public string stringEncrypt(string original, int encryptor) {
		string encryptedString;
		switch(encryptor) {
			case 0:
				encryptedString = vignereEncrypt(original);
				break;
			case 1:
				encryptedString = substitutionEncrypt(original);
				break;
			case 2:
				encryptedString = oneTimePadEncrypt(original);
				break;
			case 3:
				encryptedString = CaesarEncrypt(original);
				break;
			case 4:
				encryptedString = AtbashEncrypt(original);
				break;
		}
		
		return encryptedString;
	}
}

Class to be inserted

/**
To be added to obfuscated app code, then obfuscate it too
**/
public class Decryptor {
	
	public string decrypt(string base64String) {
		//base64 decode
		byte[] decodedBytes = Base64.getDecoder().decode(base64String);
		string decodedString = new String(decodedBytes);
		
		//get encryptor
		int toSwitch = Character.getNumericValue(decodedString.charAt(0));
		
		//get rid of encryptor
		string onlyEncryption = decodedString.substring(1);
		
		switch(toSwitch) {
			case 0:
				decryptedString = vignereDecrypt(onlyEncryption);
				break;
			case 1:
				decryptedString = substitutionDecrypt(onlyEncryption);
				break;
			case 2:
				decryptedString = oneTimePadDecrypt(onlyEncryption);
				break;
			case 3:
				decryptedString = CaesarDecrypt(onlyEncryption);
				break;
			case 4:
				decryptedString = AtbashDecrypt(onlyEncryption);
				break;
		}
	}
	
	public int intDecrypt(string obfuscatedInt) {
		//TODO: insert or replace with Sejal's number decryptor, remember to change the modification the tool does
	}
}

Code in our tool to insert Decryptor into app

/**
inserts the Decryptor into the app files
**/
public void insertDecryptor() throws IOException {
	BufferedReader reader = new BufferedReader(new FileReader("/ourtool/Decryptor.java"));
	BufferedWriter writer = new BufferedWriter(new FileWriter(new File("/FindFood/app/src/main/java/nz/co/g1/a702/findfood/ecryptor.java")));

	String line = null;
	while ((line=reader.readLine()) != null) {
		writer.write(line);
	}

	reader.close(); 
	writer.close();
}

Data obfuscation technique methods used:

• AtbashEncrypt, AtbashDecrypt
• substitutionEncrypt, substitutionDecrypt
• CaesarEncrypt, CaesarDecrypt
• vigenereEncrypt, vigenereDecrypt
• oneTimePadEncrypt, oneTimePadDecrypt

utility methods:

• generateAtbashOrderedString
• convertToAlphabetIntegerArray
• encryptDigit, decryptDigit (for numbers)
• generateNumberEncryptionHashMap