How Can I Discreetly Hide Strings in Binary Code?

How to Discreetly Conceal a String within Binary Code

Introduction:

Hiding strings within executable files can provide an extra layer of protection for sensitive data such as encryption keys. However, naively storing strings can make them easily discoverable. This article explores a technique to obfuscate strings in compiled binaries, making them difficult to locate.

The Problem:

Compiling code often stores strings as plain text in the program's data section. This makes it straightforward for attackers to identify and extract sensitive information. For instance, an encryption key stored as a constant string can be vulnerable to unauthorized access.

Obfuscating the String:

Rather than storing the string as a constant, this method uses a custom macro to encrypt and store it within the data section. The encryption algorithm involves bitwise XOR operations, resulting in an obfuscated version of the original string.

Implementing the Macro:

The macro operates as follows:

• The input string is converted into a sequence of character literals.
• Each character literal is XOR-ed with a seed value to create an encrypted byte.
• The encrypted bytes are stored in an array.
• The array is returned as a string literal.

Example Implementation:

The provided C code demonstrates this technique:

#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'))

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

Advantages:

• The obfuscated string becomes indistinguishable from other encrypted data in the binary.
• The encryption process is reversible, allowing the original string to be recovered.
• The macro-based approach simplifies implementation and ensures consistency.

Conclusion:

This technique effectively hides strings within compiled binaries, making their discovery and extraction more challenging. While it does not render the data inaccessible to determined attackers, it provides an additional layer of protection that can contribute to the security of critical information.

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