How Can We Effectively Obfuscate Strings in Binary Code to Protect Sensitive Data?

How to Obfuscate Strings in Binary Code

Protecting sensitive data in binary executables is sometimes necessary, such as concealing encryption keys to prevent their retrieval. However, storing strings in plain text within the binary makes them vulnerable. This raises the question: can we hide strings while maintaining functionality?

Conventional Hiding Methods

A straightforward but inefficient approach is manually storing each character individually, as seen below:

char encryptionKey[30];
int n = 0;
encryptionKey[n++] = 'M';
encryptionKey[n++] = 'y';
...

However, this solution is cumbersome and not ideal.

Boosting String Obfuscation

To improve upon the previous method, we can leverage the Boost Preprocessor Library to achieve more seamless and efficient string obfuscation. Consider the following code:

#include "HideString.h"

DEFINE_HIDDEN_STRING(EncryptionKey, 0x7f, ('M')('y')(' ')('s')('t')('r')('o')('n')('g')(' ')('e')('n')('c')('r')('y')('p')('t')('i')('o')('n')(' ')('k')('e')('y'))
DEFINE_HIDDEN_STRING(EncryptionKey2, 0x27, ('T')('e')('s')('t'))

int main() {
    std::cout << GetEncryptionKey() << std::endl;
    std::cout << GetEncryptionKey2() << std::endl;
    return 0;
}

In this updated code:

• HideString.h contains the necessary macros and templates for obfuscation.
• DEFINE_HIDDEN_STRING is used to define obfuscated string constants.

This solution employs encryption to hide the characters, making it more resistant to detection through simple scanning. Additionally, it is more succinct and maintainable than manually constructing arrays of characters.

Obfuscated Data Example

The resulting obfuscated string "My strong encryption key" appears as follows in the binary code:

0x00B0200C  32 07 5d 0f 0f 08 16 16 10 56 10 1a 10 00 08  2.]......V.....
0x00B0201B  00 1b 07 02 02 4b 01 0c 11 00 00 00 00 00 00  .....K.........

This data now exhibits seemingly random values, making it harder for attackers to pinpoint specific strings.

Conclusion

While this technique does not provide foolproof protection against determined attackers, it can significantly increase the time and effort required to uncover sensitive data in binary executables, providing an additional layer of security.

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