我需要反转功能的帮助

Question

So i have got this function.

UINT32 Encrypt(UINT32 instruction, int increment)
{
    UINT32 linstruction = _rotl(instruction, 7);
    UINT32 rinstruction = _rotr(instruction, 3);

    UINT32 key = (0x1F3D8AF * increment) ^ (rinstruction ^ linstruction);
    return (key ^ instruction);
}

I need to make a function that actually decrypts this and gets the instruction from the result using a key so it would be like.

t = encrypt(t, i);
t = decrypt(t, key);

Basically i want it to reverse the whole process of the encrypt so it decrypts it and gets me the instruction.

They are used in this function

int RbxOpEncoder::encode(Instruction op, int i, int key) {
    int orig = ConvertInstruction(op);
    int t = orig;
    switch (GET_OPCODE(op)) {
    case OP_JMP:
        t = ((Encrypt(t, i) & 0x3FFFFFF) | ((orig >> 26 & MASK1(6, 0)) << 0x1A));
    break;
    case OP_CALL:
    case OP_TAILCALL:
    case OP_CLOSURE:
    case OP_RETURN:
        t = ((Calldecrypt(t, i) & 0x3FFFFFF) | ((orig >> 26 & MASK1(6, 0)) << 0x1A));
        break;  
    }
    t = EncryptOpcode(t, key);
    return t;
}

Answer 1

You may use:

std::uint32_t decrypt(std::uint32_t instruction, int increment)
{
    instruction = instruction ^ (0x1F3D8AF * increment);

    for (int i = 0; i != 15; ++i) {
        instruction = Encrypt(instruction, 0);
    }
    return instruction;
}

And then you have

decrypt(Encrypt(value, increment), increment) == value

Demo