How do you XOR two 4-byte values in C?

Apply ^ to two uint32_t values; XOR combines them bit-by-bit, setting each result bit only where the two inputs differ.

uint32_t a = 0x12345678;
uint32_t b = 0xDEADBEEF;
// 0xCC99E897
uint32_t result = a ^ b;

XOR properties (useful in crypto/RE):

• a ^ a = 0 (anything XOR itself is zero)
• a ^ 0 = a (XOR with zero is identity)
• a ^ b ^ b = a (XOR is reversible - used in encryption!)
• a ^ b = b ^ a (commutative)

XOR swap trick (no temp variable):

// a = a ^ b
a ^= b;
// b = b ^ (a ^ b) = a
b ^= a;
// a = (a ^ b) ^ a = b
a ^= b;

Common use - simple encryption:

for (int i = 0; i < len; i++)
    // XOR with repeating key
    data[i] ^= key[i % keylen];