Example LCG String Decryption Patcher

ida_dec.py

def strdec(offset, key, leng, mult=1664525, const=1013904223):
    out = bytearray()
    
    bytes_read = ida_bytes.get_bytes(offset, leng)
    
    for i in range(len(bytes_read)):
        key = mult * key + const
        b1 = (bytes_read[i] ^ (key >> 12)) & 0xff
        out.append(b1)
    
    print(out)
    
    ida_bytes.patch_bytes(offset, bytes(out))

    
def decrypt_ida(addr):
    for xref in CodeRefsTo(addr, 0): #0x4016E6
        args = [] #order will be seed, offset, leng
        
        heads = [x for x in Heads(xref - 250, xref)] #reverse since we are looking backwards
        heads.reverse()
        for h in heads:
            if idc.print_insn_mnem(h) == 'push':
                args.append(idc.get_operand_value(h,0))
                if len(args) == 3:
                    break
        strdec(args[1], args[0], args[2])