2025吾愛解題領紅包活動(Android題解)

前言

簡單寫一下Android部份的解題思路。

第三題：Android初級題

明顯的xxtea特徵。

解密後直接得到flag

第四題：Android中級題

目標是找到秘鑰。

Java層關鍵邏輯如下，調用了Check函數來檢查密鑰。

是個native函數。

嘗試直接hook RegisterNatives，發現Check果然是動態注冊的，在0xe8c54。

Check一開始是一些反調試邏輯。

先看anti1，它調用decrypt_str解密字符串，但奇怪的是解密出來的字符串不是以\x00結尾，導致opendir直接失敗，使得後面的反調試邏輯形同虛設？( 不知是故意的還是不小心的 )

anti2、do_something1也同理，皆因為decrypt_str的問題導致後續的邏輯失效。

繼續向下跟，看到它動態計算出一個函數地址，大概率就是加密函數，最後與密文進行對比。

一開始以為動態計算的那個函數地址是固定的，後來才發現有兩個不同的地址，會隨著上面anti1、anti2、do_something1、getenv等函數返回的結果而改變。

類似蜜罐的概念，當觸發anti邏輯後，不主動殺死APP，而是改變程序的執行流，導向錯誤的分支。

func1、func2如下，前者是錯誤的分支，後者是正確的，我的環境默認會走func1。

可以看到兩者的加密方式都是相同的異或加密，不同的只有異或的值。

經測試發現，手動hook getenv、do_something1修改其參數、返回值後，程序才會走向func2。這時再hook encrypt，將正確的異或值dump下來。

function hook_dlopen(soName) {
    Interceptor.attach(Module.findExportByName(null, "dlopen"),
        {
            onEnter: function (args) {
                var pathptr = args[0];
                if (pathptr !== undefined && pathptr != null) {
                    var path = ptr(pathptr).readCString();
                    if (path.indexOf(soName) >= 0) {
                        this.is_can_hook = true;
                    }
                }
            },
            onLeave: function (retval) {
                if (this.is_can_hook) {
                    console.log("hook start...");
                    hook_func(soName)
                }
            }
        }
    );
 
    Interceptor.attach(Module.findExportByName(null, "android_dlopen_ext"),
        {
            onEnter: function (args) {
                var pathptr = args[0];
                if (pathptr !== undefined && pathptr != null) {
                    var path = ptr(pathptr).readCString();
                    if (path.indexOf(soName) >= 0) {
                        this.is_can_hook = true;
                    }
                }
            },
            onLeave: function (retval) {
                if (this.is_can_hook) {
                    console.log("hook start...");
                    hook_func(soName)
                }
            }
        }
    );
}

function hook_func(soName) {
    function hook_xorkey(base) {
        Interceptor.attach(base.add(0xE9954), {
            onLeave: function(retval) {
                console.log("[xor_key] ", hexdump(retval))
            }
        })
    }
    
    function hook_test2(base) {
        Interceptor.attach(base.add(0xE98A0), {
            onEnter: function(args) {
                console.log("[call func2] ")
            }
        })
        
        // do_something1
        Interceptor.attach(base.add(0xE74E8), {
            onEnter: function(args) {
                console.log("[call dosomething1] ")
            },
            onLeave: function(retval) {
                console.log("[dosomething1] retval: ", retval)
                retval.replace(0);
                console.log("[dosomething1] retval: ", retval)
            }
        })
        
        Interceptor.attach(Module.findExportByName(null, "getenv"), {
            onEnter: function(args) {
                let a0 = args[0].readCString();
                if (a0.indexOf("name") != -1) {
                    Memory.writeUtf8String(args[0], "name");
                    this.flag = true
                    console.log("[getenv] a0: ", args[0].readCString())
                }
            },
            onLeave: function(retval) {
                if (this.flag) {
                    console.log("retval: ", retval.readCString())
                }
            }
        })
    }

    var base = Module.findBaseAddress(soName);

    hook_xorkey(base);
    hook_test2(base);
}

function main() {
    hook_dlopen("libwuaipojie2025_game.so")
}

setImmediate(main)

最終解密腳本：

xor_key1 = [0x2E, 0x4B, 0xEE, 0xC8, 0xE0, 0x95, 0x88, 0x47, 0xB0, 0x72, 0x1B, 0x68, 0x40, 0xD0, 0x0A, 0x84]
# xor_key2 = [0x27, 0xAF, 0xF3, 0xA7, 0xA1, 0x64, 0x51, 0xC3, 0x67, 0x6D, 0x19, 0x04, 0xE9, 0x58, 0xE9, 0x6F]
xor_key2 = [0x77, 0x70, 0x8a]

xor_key_list = [xor_key1, xor_key2]

data1 = 0x72ECF89BAF8F2748
data2 = 0xB63AE26B0C720798
data3 = 0xF75942
enc = data1.to_bytes(8, 'little') + data2.to_bytes(8, 'little') + data3.to_bytes(3, 'little')
enc = bytearray(enc)

xor_keylist_idx = 0
xor_key_idx = 0
flag = ""
for i in range(len(enc)):
    if (i & 0xf) == 0:
        xor_key = xor_key_list[xor_keylist_idx]
        xor_keylist_idx += 1
        xor_key_idx = 0
    flag += chr(xor_key[xor_key_idx] ^ enc[i])
    xor_key_idx += 1

print("flag: ", flag)

輸出：flag: flag{md5(uid+2025)}

第六題：Windows & Android高級題

Java層分析

先看看題目描述，要幾個重點：

1. flag格式為flag{XXXXX-XXXXX-XXXXX-XXXXX}，其中X要麼是大寫字母，要麼是數字。
2. 不同UID對應不同的Flag，可能有多個解。
3. SISC中的S意為堆棧。

再看看APP，要求輸入UID和Flag。

用新版jeb查看Java層邏輯( Java層有混淆，jeb能忽略部份混淆，方便分析 )，發現調用check函數來檢查，參考分別是UID和Flag。

check是Native函數。

vm初始化

native層的check是靜態注冊的，能直接搜到。

繼續深入分析( 配合動調來遂一分析每個函數的作用 )。

init_some_data函數如下，結合後面的分析可以知道，這裡是在初始化vm虛擬機的opcodes，存放在a1[0xC000 ~ 0xC200]。

將a1記為vm_ctx，意指vm虛擬機的上下文空間。

start_vm

初始化完成後便會調用start_vm正式啟動虛擬機進行計算。

一開始會通過一些運算獲取_opcode和arg，前者是操作碼、後者是一些固定的參數( 在不同的操作碼中都有不同的含義 )。

接著就是vm最經典的一大段switch，每個case對應不同的handler，實現了不同的功能。

每個handler裡基本上都會用到vm_ctx[0x10002]，一些參數、中間值、計算結果都會存放在vm_ctx[0x10002]指向的位置。

而且可以看到vm_ctx[0x10002] + 4、vm_ctx[0x10002] - 4等等的運算，再結合題目的描述，可以猜測vm_ctx[0x10002]相當於sp( 棧指針 )，該虛擬機的所有運算操作都會在它自己維護的棧中進行( 沒有寄存器的概念 )。

vm handler分析與還原

大部份handler的實現都比較簡單，配合動調很容易就可以分析出來。

記錄幾個沒那麼容易看出來的handler。

handler7：&v26[-arg]相當於&v26 - arg，這裡是在將棧頂元素與棧頂後arg個元素交換。

handler22：注意_pc += (char)arg，對應匯編是ADD W11, W11, W12,SXTB，其中SXTB是對W12的修飾符，表示將W12的最低8位進行符號擴展，在還原handler時要特別留意這一點。

花億點時間，還原所有handler，實現一個簡單的vm解釋器：

def write_mem_str(addr, content):
    global vm_ctx
    if type(content) == str:
        for i in range(len(content)):
            vm_ctx[addr + i] = ord(content[i])
    else:
        raise Exception("TODO")
    return addr

def write_mem_word(addr, content):
    global vm_ctx
    for i in range(2):
        vm_ctx[addr + i] = content & 0xFF
        content >>= 8

def write_mem_arr(addr, arr):
    global vm_ctx
    for i in range(len(arr)):
        vm_ctx[addr + i] = arr[i]

def write_mem_dword(addr, content):
    global vm_ctx
    for i in range(4):
        vm_ctx[addr + i] = content & 0xFF
        content >>= 8

def read_mem_dword(addr):
    global vm_ctx
    return vm_ctx[addr] | (vm_ctx[addr + 1] << 8) | (vm_ctx[addr + 2] << 16) | (vm_ctx[addr + 3] << 24)

def read_mem_word(addr):
    global vm_ctx
    return vm_ctx[addr] | (vm_ctx[addr + 1] << 8)

def read_mem_byte(addr):
    global vm_ctx
    return vm_ctx[addr]

def push_data(data):
    global vm_ctx
    sp = read_mem_word(0x10002)
    tmp = sp + 4
    write_mem_word(0x10002, tmp)
    write_mem_dword(tmp, data)

def pop_data():
    global vm_ctx
    sp = read_mem_word(0x10002)
    data = read_mem_dword(sp)
    write_mem_word(0x10002, sp - 4)
    return data

def read_sp_data():
    sp = read_mem_word(0x10002)
    data = read_mem_dword(sp)
    return data

def set_sp_data(data):
    sp = read_mem_word(0x10002)
    write_mem_dword(sp, data)

def load_opcodes():
    global vm_ctx
    with open("./dump/opcodes", mode = "rb") as f:
        opcodes = bytearray(f.read())
        for i in range(len(opcodes)):
            vm_ctx[0xC000 + i] = opcodes[i]

def hex_to_negative(value, bits = 8):
    # 檢查符號位
    if value & (1 << (bits - 1)):
        # 如果是負數，計算其補碼
        value = value - (1 << bits)
    return value

def start_vm():
    global vm_ctx, pc, arg, v13

    pc = None
    arg = None
    v13 = None

    def handler_0_xor():
        n1 = pop_data()     # *sp
        n2 = read_sp_data() # *(sp - 1)
        res = n1 ^ n2
        set_sp_data(res)
        print(f"[h0_xor]\t pop, *sp = {hex(n2)} ^ {hex(n1)} = {hex(res)}")

    def handler_1_opposite():
        n = read_sp_data()
        set_sp_data(-n)
        print(f"[h1_opposite]\t *sp = -{hex(n)}")
    
    def handler_2_subsp():
        sp = read_mem_word(0x10002)
        write_mem_word(0x10002, sp - 4 * arg)
        print(f"[h2_subsp]\t sp -= {4 * arg}")
    
    def handler_4_orr():
        n1 = pop_data()     # *sp
        n2 = read_sp_data() # *(sp - 1)
        res = n1 | n2
        set_sp_data(res)
        print(f"[h4_orr]\t pop, *sp = {hex(n2)} | {hex(n1)} = {hex(res)}")
    
    def handler_5_(): # nglog: maybe some problem
        global pc
        sp = read_mem_word(0x10002)
        v23 = read_sp_data()
        v24 = sp - 8 - 4 * arg + 4
        pc = read_mem_dword(sp - 4)
        write_mem_word(0x10002, v24)
        write_mem_dword(v24, v23)
        print(f"[h5_]\t sp = {hex(v24)}, [{hex(v24)}] = {hex(v23)}, pc = {hex(pc)}")
    
    def handler_6_noeq(): # nglog
        n1 = pop_data()     # *sp
        n2 = read_sp_data() # *(sp - 1)
        res = n1 != n2
        set_sp_data(res)
        print(f"[h6_noeq]\t pop, *sp = {hex(n2)} != {hex(n1)} = {hex(res)}")
    
    def handler_7_swap(): # nglog: some problem
        global arg
        sp = read_mem_word(0x10002)
        n1 = read_mem_dword(sp)     # sp
        n2 = read_mem_dword(sp - 4 * arg) # sp - arg

        write_mem_dword(sp, n2)
        write_mem_dword(sp - 4 * arg, n1)

        print(f"[h7_swap]\t swap(sp, sp - {arg}) -> swap({hex(n1), hex(n2)})")
    
    def handler_8_and():
        n1 = pop_data()     # *sp
        n2 = read_sp_data() # *(sp - 1)
        res = n1 & n2
        set_sp_data(res)
        print(f"[h8_and]\t pop, *sp = {hex(n2)} & {hex(n1)} = {hex(res)}")
    
    def handler_9_lsl():
        sp_data = read_sp_data()
        set_sp_data(sp_data << arg)
        print(f"[h9_lsl]\t *sp = *sp << arg = {hex(sp_data)} << {arg} = {hex(sp_data << arg)}")

    def handler_10_not():
        sp_data = read_sp_data()
        set_sp_data(~sp_data)
        print(f"[h10_not]\t *sp = ~(*sp) = ~{hex(sp_data)} = {hex(~sp_data & 0xffffffff)}")
    
    def handler_12_add():
        n1 = pop_data()     # *sp
        n2 = read_sp_data() # *(sp - 1)
        res = n1 + n2
        set_sp_data(res)
        print(f"[h12_add]\t pop, *sp = {hex(n2)} + {hex(n1)} = {hex(res)}")
    def handler_14_():
        global pc
        pc += hex_to_negative(arg)
        print(f"[h14_]\t pc += {hex_to_negative(arg)}")
    def handler_15_():
        write_mem_word(0x10004, 257)
        print("[h15_]\t write_mem_word(0x10004, 257)")
    
    def handler_17_lsr():
        sp_data = read_sp_data()
        set_sp_data(sp_data >> arg)
        print(f"[h17_lsr]\t *sp = *sp >> arg = {hex(sp_data)} >> {arg} = {hex(sp_data >> arg)}")

    def handler_18_mod():
        n1 = pop_data()     # *sp
        n2 = read_sp_data() # *(sp - 1)
        res = n2 % n1
        set_sp_data(res)
        print(f"[h18_mod]\t pop, *sp = {hex(n2)} % {hex(n1)} = {hex(res)}")
    
    def handler_20_dword2byte():
        sp = read_mem_word(0x10002)
        sp_data = read_mem_byte(sp)
        set_sp_data(sp_data)
        print(f"[h20_dword2byte]\t *(dword*)sp = *(byte*)sp = {hex(sp_data)}")

    def handler_21_mul():
        n1 = pop_data()     # *sp
        n2 = read_sp_data() # *(sp - 1)
        res = n1 * n2
        set_sp_data(res)
        print(f"[h21_mul]\t pop, *sp = {hex(n2)} * {hex(n1)} = {hex(res)}")

    def handler_22_pushpc(): # nglog
        global pc
        sp = read_mem_word(0x10002)
        pc_ = pc
        pc += hex_to_negative(arg)
        v34 = sp + 4
        write_mem_word(0x10002, v34)
        write_mem_dword(v34, pc_)
        print(f"[h22_pushpc]\t push(pc) -> push({hex(pc_)}), pc += {hex_to_negative(arg)}")
    
    def handler_23_eq(): # nglog
        global pc
        sp = read_mem_word(0x10002)
        v16 = sp - 4
        v15 = sp - 8
        n1 = read_mem_dword(sp)
        n2 = read_mem_dword(sp - 4)
        write_mem_word(0x10002, v15)
        if (v13 == 25) == (n1 == n2):
            print(f"[h23_eq]\t sp = sp - 8")
            return
        
        if arg & 0xFFFFFF00 != 0:
            raise Exception("TODO")

        pc += hex_to_negative(arg)
        print(f"[h23_eq]\t sp = sp - 8, pc += {hex_to_negative(arg)} ({hex(arg)})")

    def handler_26_getinput():
        n1 = pop_data()     # *sp
        n2 = read_sp_data() # *(sp - 1)
        res = read_mem_byte(n1 + n2)
        set_sp_data(res)
        print(f"[h26_getinput]\t pop, *sp = vm_ctx[{hex(n2)} + {hex(n1)}] = {hex(res)}")
    
    def handler_27_pusharg():
        global arg
        sp = read_mem_word(0x10002)
        orig_arg = arg
        arg = read_mem_dword(sp - 4 * arg)
        push_data(arg)
        print(f"[h27_pusharg]\t push({hex(arg)})  arg == [sp - 4 * {orig_arg}]")
    
    def handler_29_pusharg2(): # nglog
        push_data(arg)
        print(f"[h29_pusharg2]\t push({hex(arg)})")

    def handler_30_sub1():
        sp_data = read_sp_data()
        set_sp_data(sp_data - 1)
        print(f"[h30_sub1]\t *sp = *sp - 1 = {hex(sp_data)} - 1 = {hex(sp_data - 1)}")
    
    pc = read_mem_word(0x10000)
    
    while True:
        pc_1 = pc + 1
        cur_opcode = read_mem_byte(pc)
        arg = cur_opcode & 7
        if arg != 7:
            pc += 1
            v13 = cur_opcode >> 3
            _opcode = v13 - 1
        else:
            pc += 2
            arg = read_mem_byte(pc_1)
            v13 = cur_opcode >> 3
            _opcode = v13 - 1
            if v13 - 1 > 0x1E:
                raise Exception("TODO")
                break
        if _opcode == 0:
            handler_0_xor()
        elif _opcode == 1:
            handler_1_opposite()
        elif _opcode == 2:
            handler_2_subsp()
        elif _opcode == 3 or _opcode == 25:
            continue
        elif _opcode == 4:
            handler_4_orr()
        elif _opcode == 5:
            handler_5_()
        elif _opcode == 6:
            handler_6_noeq()
        elif _opcode == 7:
            handler_7_swap()
        elif _opcode == 8:
            handler_8_and()
        elif _opcode == 9:
            handler_9_lsl()
        elif _opcode == 10:
            handler_10_not()
        elif _opcode == 12:
            handler_12_add()
        elif _opcode == 14:
            handler_14_()
        elif _opcode == 15:
            handler_15_()
            break
        elif _opcode == 17:
            handler_17_lsr()
        elif _opcode == 18:
            handler_18_mod()
        elif _opcode == 20:
            handler_20_dword2byte()
        elif _opcode == 21:
            handler_21_mul()
        elif _opcode == 22:
            handler_22_pushpc()
        elif _opcode == 23 or _opcode == 24:
            handler_23_eq()
        elif _opcode == 26:
            handler_26_getinput()
        elif _opcode == 27:
            handler_27_pusharg()
        elif _opcode == 29:
            handler_29_pusharg2()
        elif _opcode == 30:
            handler_30_sub1()
        else:
            print("else _opcode: ", _opcode)
            raise Exception("TODO")
            break
    
    write_mem_word(0x10000, pc)
    res = read_sp_data()
    return res

# init vm_ctx
vm_ctx = [0] * 0x10006

load_opcodes()

write_mem_dword(0x10000, 0x8000C000)
write_mem_word(0x10004, 0)

write_mem_arr(0x204 * 0x10, [0x00, 0x03, 0x0F, 0x20, 0x0D, 0x02, 0x23, 0x06, 0x1B, 0x14,0x0E, 0x01, 0x16, 0x19, 0x08, 0x12])
write_mem_arr(0x205 * 0x10, [0x1F, 0x17, 0x24, 0x0B, 0x1E, 0x07, 0x1A, 0x05, 0x18, 0x1D, 0x22, 0x00, 0x00, 0x00, 0x00, 0x00])
write_mem_arr(0x203 * 0x10, [0x09, 0x0A, 0x10, 0x15, 0x21, 0x13, 0x0C, 0x04, 0x11, 0x1C, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00])

write_mem_str(0x1000, "flag{44444-44444-44444-44444}") # input flag

push_data(1898208) # uid
push_data(0x1000)
push_data(0x2000)

res = start_vm()
print("[res]: ", hex(res))

提醒：flag格式為flag{XXXXX-XXXXX-XXXXX-XXXXX}，其中X要麼是大寫字母，要麼是數字。

腳本中的測試flag要記得符合這個格式，腳本的輸出日志記為vm.log。

加密邏輯分析

前置：在動調的過程中發現handler26會獲取輸入的Flag，加密邏輯大概會在那附近。

在vm.log中搜h26_getinput定位到相關位置，首先判斷了input是否flag{ }的格式。

[h26_getinput]	 pop, *sp = vm_ctx[0x1000 + 0x0] = 0x66  # 'f'
[h0_xor]	 pop, *sp = 0x66 ^ 0x66 = 0x0
[h4_orr]	 pop, *sp = 0x0 | 0x0 = 0x0
[h29_pusharg2]	 push(0x6c)
[h27_pusharg]	 push(0x1000)  arg == [sp - 4 * 3]
[h29_pusharg2]	 push(0x1)
[h26_getinput]	 pop, *sp = vm_ctx[0x1000 + 0x1] = 0x6c  # 'l'
[h0_xor]	 pop, *sp = 0x6c ^ 0x6c = 0x0
[h4_orr]	 pop, *sp = 0x0 | 0x0 = 0x0
[h29_pusharg2]	 push(0x61)
[h27_pusharg]	 push(0x1000)  arg == [sp - 4 * 3]
[h29_pusharg2]	 push(0x2)
[h26_getinput]	 pop, *sp = vm_ctx[0x1000 + 0x2] = 0x61  # 'a'
[h0_xor]	 pop, *sp = 0x61 ^ 0x61 = 0x0
[h4_orr]	 pop, *sp = 0x0 | 0x0 = 0x0
[h29_pusharg2]	 push(0x67)
[h27_pusharg]	 push(0x1000)  arg == [sp - 4 * 3]
[h29_pusharg2]	 push(0x3)
[h26_getinput]	 pop, *sp = vm_ctx[0x1000 + 0x3] = 0x67   # 'g'
[h0_xor]	 pop, *sp = 0x67 ^ 0x67 = 0x0
[h4_orr]	 pop, *sp = 0x0 | 0x0 = 0x0
[h29_pusharg2]	 push(0x7b)
[h27_pusharg]	 push(0x1000)  arg == [sp - 4 * 3]
[h29_pusharg2]	 push(0x4)
[h26_getinput]	 pop, *sp = vm_ctx[0x1000 + 0x4] = 0x7b   # '{'
[h0_xor]	 pop, *sp = 0x7b ^ 0x7b = 0x0
[h4_orr]	 pop, *sp = 0x0 | 0x0 = 0x0
[h29_pusharg2]	 push(0x7d)
[h27_pusharg]	 push(0x1000)  arg == [sp - 4 * 3]
[h29_pusharg2]	 push(0x1c)
[h26_getinput]	 pop, *sp = vm_ctx[0x1000 + 0x1c] = 0x7d  # '}'
[h0_xor]	 pop, *sp = 0x7d ^ 0x7d = 0x0

從input[5]開始才是真正的內容，對input[5~8]的運算可以總結為：查表、自減、乘0x24。

# 處理input[5]
[h26_getinput]	 pop, *sp = vm_ctx[0x1005 + 0x0] = 0x34     
[h26_getinput]	 pop, *sp = vm_ctx[0x2000 + 0x34] = 0x21  # table[input[5]] == 0x21
[h27_pusharg]	 push(0x21)  arg == [sp - 4 * 0]
[h29_pusharg2]	 push(0x0)
[h23_eq]	 sp = sp - 8
[h12_add]	 pop, *sp = 0x0 + 0x21 = 0x21                   # tmp = 0 + table[input[5]]
[h30_sub1]	 *sp = *sp - 1 = 0x21 - 1 = 0x20              # tmp -= 1
[h7_swap]	 swap(sp, sp - 1) -> swap(('0x20', '0x0'))
[h29_pusharg2]	 push(0x1)
[h12_add]	 pop, *sp = 0x0 + 0x1 = 0x1
[h14_]	 pc += -24
[h27_pusharg]	 push(0x1)  arg == [sp - 4 * 0]
[h27_pusharg]	 push(0x5)  arg == [sp - 4 * 6]
[h23_eq]	 sp = sp - 8
[h7_swap]	 swap(sp, sp - 1) -> swap(('0x1', '0x20'))
[h29_pusharg2]	 push(0x24)
[h21_mul]	 pop, *sp = 0x20 * 0x24 = 0x480                # tmp *= 0x24

# 處理input[6]
[h26_getinput]	 pop, *sp = vm_ctx[0x1005 + 0x1] = 0x34
[h26_getinput]	 pop, *sp = vm_ctx[0x2000 + 0x34] = 0x21
[h27_pusharg]	 push(0x21)  arg == [sp - 4 * 0]
[h29_pusharg2]	 push(0x0)
[h23_eq]	 sp = sp - 8
[h12_add]	 pop, *sp = 0x480 + 0x21 = 0x4a1                # tmp += table[input[6]]
[h30_sub1]	 *sp = *sp - 1 = 0x4a1 - 1 = 0x4a0            # tmp -= 1
# same...

對input[9]有特別的處理，查表、自減操作仍舊保留，不同的是後面會判斷tmp >> 25是否不為0，若是則進行自加、取餘操作。

取餘操作中的模數，會根據輸入的UID不同而變化，即固定UID對應固定的模數。

( 注：以-分隔的每組字串的最個一個元素都是這樣處理的 )

# 以下日志不是連續的, 為了好看將其放在一起
[h26_getinput]	 pop, *sp = vm_ctx[0x1005 + 0x4] = 0x34
[h26_getinput]	 pop, *sp = vm_ctx[0x2000 + 0x34] = 0x21 # 查表
[h12_add]	 pop, *sp = 0x34b8e80 + 0x21 = 0x34b8ea1
[h30_sub1]	 *sp = *sp - 1 = 0x34b8ea1 - 1 = 0x34b8ea0   # 自減

[h17_lsr]	 *sp = *sp >> arg = 0x34b8ea0 >> 25 = 0x1      # 判斷tmp >> 25是否不為0
[h12_add]	 pop, *sp = 0x34b8ea0 + 0x1 = 0x34b8ea1        # 自加
[h18_mod]	 pop, *sp = 0x34b8ea1 % 0xb05f17 = 0x8a1245    # 取餘

以-作為分隔符，每組處理完後會以|來融合。

[h4_orr]	 pop, *sp = 0x1fc3d5 | 0x8a1245 = 0x9fd3d5

最後會自減、異或0xc15303fb，這個值是固定的。

[h30_sub1]	 *sp = *sp - 1 = 0x19fffff - 1 = 0x19ffffe
# ...
[h0_xor]	 pop, *sp = 0x19ffffe ^ 0xc15303fb = 0xc0ccfc05
[h5_]	 sp = 0x8014, [0x8014] = 0xc0ccfc05, pc = 0xc088
[h15_]	 write_mem_word(0x10004, 257)
[res]:  0xc0ccfc05

綜合上述分析，可以大概用Python還原出加密邏輯：

tables = [0x09, 0x0A, 0x10, 0x15, 0x21, 0x13, 0x0C, 0x04, 0x11, 0x1C, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x03, 0x0F, 0x20, 0x0D, 0x02, 0x23, 0x06, 0x1B, 0x14,0x0E, 0x01, 0x16, 0x19, 0x08, 0x12, 0x1F, 0x17, 0x24, 0x0B, 0x1E, 0x07, 0x1A, 0x05, 0x18, 0x1D, 0x22, 0x00, 0x00, 0x00, 0x00, 0x00]
mod_arr = [0xa91f91, 0xb66962, 0xf19ad9, 0xef305d]  # 我的UID對應的模數

def encrypt(input):

    length = len(input)
    res = 0
    tmp = 0
    i = 0
    mi = 0
    while True:
        if i >= length:
            res |= tmp
            print("tmp res: ", hex(res))
            break

        if input[i] == '-':
            res |= tmp
            print("tmp res: ", hex(res))
            tmp = 0
            i += 1
            continue
        table_idx = ord(input[i]) - 0x30
        if table_idx < 0 or table_idx >= 0x30:
            sep = input.find("-", i)
            if sep == -1:
                break
            i = sep
            tmp |= 1
            continue
        
        tmp += tables[table_idx]
        tmp -= 1
        if i + 1 < length and input[i + 1] != '-':
            tmp *= 0x24
        else:
            if (tmp >> 25) != 0:
                tmp += 1
                tmp %= mod_arr[mi]
                mi += 1
        print("tmp: ", hex(tmp))
        i += 1

    res -= 1
    res ^= 0xc15303fb
    print(res)
    print("res: ", hex(res))

encrypt("44444-RRRRR-RRRRR-RRRRR")

最終解密

基於上述加密腳本，似乎無法直接反推出對應的解密邏輯，而且題目描述中提到有多個解也認證了這一點。

密文是0x3EACFC04，(0x3EACFC04 ^ 0xc15303fb) == 0xFFFFFFFF，而-1的16進制正是該值，因此只要在最終的自減前，res的值為0，即可滿足等式。

上面提到，以-分隔的每個字串的最個一個元素都會進行取餘的操作( 前提是>>25不為0 )，這一步就可以很方便讓tmp歸0。

以-分隔的每組數據計算過程如下，現在的目標是讓tmp等於0，因此d + input_[4]必須是target的整數倍。

此時問題轉化為如何讓d + input_[4] == n * target，其中n、target都是已知的。

( 注：input_[i]指input[i]查表後的結果、target是每組的模數 )

a = (input_[0] - 1) * 0x24
b = (a + input_[1] - 1) * 0x24
c = (b + input_[2] - 1) * 0x24
d = (c + input_[3] - 1) * 0x24
tmp = (d + input_[4]) % target

以下腳本用來求input_[0 ~ 4]這幾個未知量( 初始為0 )，原理如下：

1. 先爆破input_[0]，若input_[0]為i會使func函數返回值>0且input_[0]為i+1會使func函數返回值<0，則代表i就是input_[0]的最大值，也是input_[0]其中一個可能的值。
2. 確定了input_[0]後，用同樣方法確定input_[1 ~ 4]。
3. 最終可以確定input_[0 ~ 4]，由此反查tables來確定input[0 ~ 4]字符串。

注：當input_[j]被確定為0時，是不合理的，要將input_[j - 1] -= 1，然後再重新計算input_[j]的最大值。

# tables的範圍為 (0x0, 0x24]
tables = [0x09, 0x0A, 0x10, 0x15, 0x21, 0x13, 0x0C, 0x04, 0x11, 0x1C, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x03, 0x0F, 0x20, 0x0D, 0x02, 0x23, 0x06, 0x1B, 0x14,0x0E, 0x01, 0x16, 0x19, 0x08, 0x12, 0x1F, 0x17, 0x24, 0x0B, 0x1E, 0x07, 0x1A, 0x05, 0x18, 0x1D, 0x22, 0x00, 0x00, 0x00, 0x00, 0x00]

def func(target, input_):
    a = (input_[0] - 1) * 0x24
    b = (a + input_[1] - 1) * 0x24
    c = (b + input_[2] - 1) * 0x24
    d = (c + input_[3] - 1) * 0x24
    res = target - d
    return res

def func2(target):
    input_ = [0] * 4
    res = []
    for j in range(4):
        for i in range(0x25):
            input_[j] = i
            a = func(target, input_)
            input_[j] = i + 1
            b = func(target, input_)
            if a > 0 and b < 0:
                if i == 0:
                    input_[j - 1] -= 1
                    res[len(res) - 1] = chr(0x30 + tables.index(input_[j - 1]))
                    continue
                input_[j] = i
                t = tables.index(i)
                if t == -1:
                    raise Exception("??")
                res.append(chr(0x30 + t))
                break

    res.append(chr(tables.index(func(target, input_)) + 0x30))
    return "".join(res)
    
# 0x2A47E44 = 4 * 0xa91f91 ( 0xa91f91是第1個模數 )
print(func2(0x2A47E44) + '-' + func2(0x2d9a588) + '-' + func2(0x2D4D08B) + '-' + func2(0x2CD9117))

運行腳本得到一個可行的Flag為HB0P6-Y84V7-YSWDH-9RZPB：

第八題：Android高級題

直接hook RegisterNatives，看到flag驗證邏輯在lib52pojie.so!0x134d4。

[RegisterNatives] java_class: com.wuaipojie.crackme2025.MainActivity name: checkSn sig: (Ljava/lang/String;)Z 
									fnPtr: 0x7ebed554d4  fnOffset: 0x7ebed554d4 lib52pojie.so!0x134d4  callee: 0x7ebed553d8 lib52pojie.so!0x133d8

看到一堆~、^、|操作，但其實它們並非加密邏輯，而是類似ollvm裡的「指令替換」混淆，也叫MBA表達式。

簡單來說就是將一段很簡單的指令( 如a + b )，通過疊加~、^、|等操作符轉換成完全等價的複雜指令。

由於沒有解混淆的思路，因此只能直接動調慢慢看邏輯。

調用get_input_8取了input的一部份，然後傳入encrypt。

encrypt中主要分成3部份，先看encrypt_part1。

encrypt_part1

input.n128_u64[0]是低64位，代表傳入的flag，input.n128_u64[1]是高64位，用來存放結果。

只看與input有關的，hook發現input.n128_u64[0]每輪固定左移-1，即右移1。

由此得出input.n128_u64[0]的迭代方式：input = (input >> 1) & (2 ** 64 - 1)

input.n128_u64[1]只與tmp1有關。

frida stalker打印tmp1、input_1.n128_u64[1]+=的那個值，發現要將tmp1看成2進制位，每輪都會拼到input_1.n128_u64[1]的低位。

即input1 = (input1 << 1) | tmp1，而tmp1其實就是取input.n128_u64[0]的最低位。

[2] x26: 0x1  x27: 0x3332317b67616c66
[3] x8(tmp1): 0x0
[5] x8: 0x0    // 0
0 0 0 0 0 0 0 0
33 b6 b0 b3 bd 18 99 19

[2] x26: 0x1  x27: 0x199918bdb3b0b633
[3] x8(tmp1): 0x1
[5] x8: 0x1    // 01
0 0 0 0 0 0 0 0
19 5b d8 d9 5e 8c cc c

[2] x26: 0x1  x27: 0xccc8c5ed9d85b19
[3] x8(tmp1): 0x1
[5] x8: 0x3    // 011
1 0 0 0 0 0 0 0
8c 2d ec 6c 2f 46 66 6

[2] x26: 0x1  x27: 0x666462f6cec2d8c
[3] x8(tmp1): 0x0
[5] x8: 0x6     // 0110
3 0 0 0 0 0 0 0
c6 16 76 b6 17 23 33 3

最終encrypt_part1可以簡化為：

def encrypt_part1(input):
    input1 = 0
    v18 = 1

    for i in range(0x40):
        # tmp1 = ((v18 + input) ^ -(v18 | input)) + 2 * ((v18 & input) - ((v18 + input) | -(v18 | input)))
        tmp1 = input & v18
        input = (input >> 1) & (2 ** 64 - 1)

        input1 = (input1 << 1) | tmp1
        print(tmp1)

    return input1

encrypt_part2

encrypt_part2的邏輯比encrypt_part1複雜得多，繼續像上面那樣分析實在不太理智( 有心無力 )，本來都打算放棄了，結果當天晚上吾愛放出了提示：

2025.02.10  16:45 【春节】解题领红包之八 {Android 高级题} 对称算法，需要识别出算法类型，找出初始化后的密钥后反推即可，对应获取奖励也减半

對稱算法，結合分析過程中看到的一些表，嘗試直接搜看看表中的數據。

發現其實是DES算法。

而且根據提示，密鑰是初始化過的。

hook encrypt，打印args[0]，發現每個QWORD剛好都是6字節大小的數據，而DES算法的round key也是48位，因此這大概率就是提示所述的初始化過的密鑰。

算法分析

DES算法：https://blog.csdn.net/nicai_hualuo/article/details/123135670

基於原版DES，遂步分析，還原到最後發現其實是3DES。完整腳本如下：( 腳本是其於上述文章改的 )

IP =  [0x3A, 0x32, 0x2A, 0x22, 0x1A, 0x12, 0x0A, 0x02, 0x3C, 0x34, 
  0x2C, 0x24, 0x1C, 0x14, 0x0C, 0x04, 0x3E, 0x36, 0x2E, 0x26, 
  0x1E, 0x16, 0x0E, 0x06, 0x40, 0x38, 0x30, 0x28, 0x20, 0x18, 
  0x10, 0x08, 0x39, 0x31, 0x29, 0x21, 0x19, 0x11, 0x09, 0x01, 
  0x3B, 0x33, 0x2B, 0x23, 0x1B, 0x13, 0x0B, 0x03, 0x3D, 0x35, 
  0x2D, 0x25, 0x1D, 0x15, 0x0D, 0x05, 0x3F, 0x37, 0x2F, 0x27, 
  0x1F, 0x17, 0x0F, 0x07]

E = [32,  1,  2,  3,  4,  5,
        4,  5,  6,  7,  8,  9,
        8,  9, 10, 11, 12, 13,
        12, 13, 14, 15, 16, 17,
        16, 17, 18, 19, 20, 21,
        20, 21, 22, 23, 24, 25,
        24, 25, 26, 27, 28, 29,
        28, 29, 30, 31, 32,  1]

P = [16,  7, 20, 21,
			29, 12, 28, 17,
			1, 15, 23, 26,
			5, 18, 31, 10,
			2,  8, 24, 14,
			32, 27, 3,  9,
			19, 13, 30, 6,
			22, 11,  4, 25]

IPR = [40, 8, 48, 16, 56, 24, 64, 32,
			  39, 7, 47, 15, 55, 23, 63, 31,
			  38, 6, 46, 14, 54, 22, 62, 30,
			  37, 5, 45, 13, 53, 21, 61, 29,
			  36, 4, 44, 12, 52, 20, 60, 28,
			  35, 3, 43, 11, 51, 19, 59, 27,
			  34, 2, 42, 10, 50, 18, 58, 26,
			  33, 1, 41,  9, 49, 17, 57, 25]

SBOX = [
    [
        [14, 4, 13, 1, 2, 15, 11, 8, 3, 10, 6, 12, 5, 9, 0, 7],
        [0, 15, 7, 4, 14, 2, 13, 1, 10, 6, 12, 11, 9, 5, 3, 8],
        [4, 1, 14, 8, 13, 6, 2, 11, 15, 12, 9, 7, 3, 10, 5, 0],
        [15, 12, 8, 2, 4, 9, 1, 7, 5, 11, 3, 14, 10, 0, 6, 13]
    ],
    [
        [15, 1, 8, 14, 6, 11, 3, 4, 9, 7, 2, 13, 12, 0, 5, 10],
        [3, 13, 4, 7, 15, 2, 8, 14, 12, 0, 1, 10, 6, 9, 11, 5],
        [0, 14, 7, 11, 10, 4, 13, 1, 5, 8, 12, 6, 9, 3, 2, 15],
        [13, 8, 10, 1, 3, 15, 4, 2, 11, 6, 7, 12, 0, 5, 14, 9]
    ],
    [
        [10, 0, 9, 14, 6, 3, 15, 5, 1, 13, 12, 7, 11, 4, 2, 8],
        [13, 7, 0, 9, 3, 4, 6, 10, 2, 8, 5, 14, 12, 11, 15, 1],
        [13, 6, 4, 9, 8, 15, 3, 0, 11, 1, 2, 12, 5, 10, 14, 7],
        [1, 10, 13, 0, 6, 9, 8, 7, 4, 15, 14, 3, 11, 5, 2, 12]
    ],
    [
        [7, 13, 14, 3, 0, 6, 9, 10, 1, 2, 8, 5, 11, 12, 4, 15],
        [13, 8, 11, 5, 6, 15, 0, 3, 4, 7, 2, 12, 1, 10, 14, 9],
        [10, 6, 9, 0, 12, 11, 7, 13, 15, 1, 3, 14, 5, 2, 8, 4],
        [3, 15, 0, 6, 10, 1, 13, 8, 9, 4, 5, 11, 12, 7, 2, 14]
    ],
    [
        [2, 12, 4, 1, 7, 10, 11, 6, 8, 5, 3, 15, 13, 0, 14, 9],
        [14, 11, 2, 12, 4, 7, 13, 1, 5, 0, 15, 10, 3, 9, 8, 6],
        [4, 2, 1, 11, 10, 13, 7, 8, 15, 9, 12, 5, 6, 3, 0, 14],
        [11, 8, 12, 7, 1, 14, 2, 13, 6, 15, 0, 9, 10, 4, 5, 3]
    ],
    [
        [12, 1, 10, 15, 9, 2, 6, 8, 0, 13, 3, 4, 14, 7, 5, 11],
        [10, 15, 4, 2, 7, 12, 9, 5, 6, 1, 13, 14, 0, 11, 3, 8],
        [9, 14, 15, 5, 2, 8, 12, 3, 7, 0, 4, 10, 1, 13, 11, 6],
        [4, 3, 2, 12, 9, 5, 15, 10, 11, 14, 1, 7, 6, 0, 8, 13]
    ],
    [
        [4, 11, 2, 14, 15, 0, 8, 13, 3, 12, 9, 7, 5, 10, 6, 1],
        [13, 0, 11, 7, 4, 9, 1, 10, 14, 3, 5, 12, 2, 15, 8, 6],
        [1, 4, 11, 13, 12, 3, 7, 14, 10, 15, 6, 8, 0, 5, 9, 2],
        [6, 11, 13, 8, 1, 4, 10, 7, 9, 5, 0, 15, 14, 2, 3, 12]
    ],
    [
        [13, 2, 8, 4, 6, 15, 11, 1, 10, 9, 3, 14, 5, 0, 12, 7],
        [1, 15, 13, 8, 10, 3, 7, 4, 12, 5, 6, 11, 0, 14, 9, 2],
        [7, 11, 4, 1, 9, 12, 14, 2, 0, 6, 10, 13, 15, 3, 5, 8],
        [2, 1, 14, 7, 4, 10, 8, 13, 15, 12, 9, 0, 3, 5, 6, 11]
    ]
]

round_keys = [222483666014355, 34094049895368, 188087828272899, 30798344234022, 20170121439688, 154109401428571, 143409192342562, 80501118078826, 126994336798112, 150086336645229, 197956095638172, 182733681792953, 11125921617955, 224782889413428, 7453516311004, 200667612718677, 114350607846426, 27979304443188, 145503975706288, 90448879766041, 10827630596124, 1245263770020, 194907790650021, 89110378318487, 38106705338630, 149997549266822, 105755390509763, 75540444135499, 215007439009096, 119720110503264, 55615706156578, 143051418949992, 222483666014355, 34094049895368, 188087828272899, 30798344234022, 20170121439688, 154109401428571, 143409192342562, 80501118078826, 126994336798112, 150086336645229, 197956095638172, 182733681792953, 11125921617955, 224782889413428, 7453516311004, 200667612718677]

def dec2binary(dec):
    res = bin(dec)[2:]
    length = len(res)
    if length < 4:
        r = 4 - length
    else:
        r = length - 4 * (length // 4)

    for i in range(r):
        res = '0' + res
    return res

def hex_to_binary_str(hex_val, n):

    def byte2binary(val):
        ret = "{:08b}".format(val)
        for i in range(8 - len(ret)):
            ret = '0' + ret
        return ret
        
    res = ""
    arr = bytearray(int.to_bytes(hex_val, n, 'little'))
    for i in range(n):
        res += byte2binary(arr[i])

    return res

def binary_str_to_hex(bin_str):
    return hex(int(bin_str, 2))[2:]

def IPExchange(input):
    res = ""
    for i in range(64):
        res += input[IP[i] - 1]

    return res

def XOR(a, b):
    if len(a) != len(b):
        raise Exception("something wrong")
    res = ""
    for i in range(len(a)):
        if a[i] == b[i]:
            res += '0'
        else:
            res += '1'
    return res

def EExchange(right):
    res = ""
    for i in range(48):  
        res += right[E[i] - 1]

    return res

def SExchange(input):
    res = ""
    for i in range(0, 48, 6):
        row = int(input[i]) * 2 + int(input[i + 5])
        col = int(input[i + 1]) * 8 + int(input[i + 2]) * 4 + int(input[i + 3]) * 2 + int(input[i + 4])
        res += dec2binary(SBOX[i // 6][row][col])
    
    return res

def PExchange(input):
    res = ""
    for i in range(32):  
        res += input[P[i] - 1]

    return res

def IPRExchange(input):
    res = ""
    for i in range(64):  
        res += input[IPR[i] - 1]

    return res

def F(right, rk):
    tmp = EExchange(right)
    tmp = XOR(tmp, rk)
    res = SExchange(tmp)
    res = PExchange(res)
    return res

def des_encrypt(input, key_start, mode):
    # mode: 0 -> enc,  1 -> dec

    tmp = IPExchange(input)

    left = tmp[0:32]
    right = tmp[32:]

    for i in range(16):
        middle = right
        if mode == 0:
            right = XOR(left, F(right, round_keys[key_start + i]))
        else:
            right = XOR(left, F(right, round_keys[key_start + 0xf - i]))
        left = middle

    cipher = right + left
    res = IPRExchange(cipher)
    return res

def convert(input):
    # input: hex val
    # dsc: 將hex val轉換成binary str, 左 -> 右 , 低 -> 高

    res = ""

    for i in range(0x40):
        res += str((input & 1))
        input >>= 1
    
    return res

def convert_re(input):
    res = ""

    for i in range(0x40):
        res = input[i] + res
    
    return res

def convert2(input, bit):
    # input: hex val
    # dsc: 將hex val轉換成binary str, 左 -> 右 , 高 -> 低

    res = ""

    for i in range(bit):
        res = str((input & 1)) + res
        input >>= 1
    return res

def convert_round_keys():
    for i in range(len(round_keys)):
        round_keys[i] = convert2(round_keys[i], 48)

def encrypt(input):
    input = convert(input)
    # print("convert input: ", binary_str_to_hex(input))

    enc = des_encrypt(input, 0, 0)
    enc = des_encrypt(enc, 16, 1)
    enc = des_encrypt(enc, 32, 0)
    print("enc: ", binary_str_to_hex(enc))
    return enc

def decrypt(input):
    input = convert2(input, 64)

    enc = des_encrypt(input, 0, 1)
    enc = des_encrypt(enc, 16, 0)
    enc = des_encrypt(enc, 32, 1)

    res = convert_re(enc)
    return binary_str_to_hex(res)

def to_flag(input):
    res = ""
    for i in range(0, len(input), 2):
        ch = chr(int(input[i: i + 2], 16))
        res = ch + res
    return res

if __name__ == "__main__":
    convert_round_keys()
    # input = 0x3332317b67616c66 # input1
    # input = 0x3231393837363534 # input2
    # input = 0x7d39383736353433 # input3
    # enc = encrypt(input)

    enc_data = [0x7C1A8B2E957A3115, 0x4B43E13562FC5DE6, 0x8346103AE93F945D]
    flag = ""
    for e in enc_data:
        t = decrypt(e)
        flag += to_flag(t)
    
    print("flag: ", flag)

輸出flag：

flag:  52PojiEHaPpynEwY3ar2025!