强网拟态2023

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# PREFACE：初赛成绩一般，车联网那个 vpn 没看懂，属于是经验不足了
# 贴一下 re 吧，其实题有点难的（但是为啥那么多解呢，还是我太菜了嘛 55555）

# fisher

前面的没什么用，把反调和格式检查过掉，然后手动改 rip 过 sha1 触发 main 里的异常处理，有一个函数里面有类似 base 变表的表，实则是自写的加密，可以把 vector 容器的符号表恢复一下方便看，逆该加密即可

encoded_flag = 'N17EHf1DWHD40DWH/f79E05EfIH1E179E1'
decoded_flag = ''
table = 'ghijklpqrstuvwxyzABCabcDEFdef0123GHI4567JKL+/MNOmnoPQRSXYZ8TUVW9' 
for c1, c2 in zip(encoded_flag[0::2], encoded_flag[1::2]):
    i1, i2 = table.index(c1), table.index(c2)
    row1, col1 = divmod(i1, 8)
    row2, col2 = divmod(i2, 8)
    if row1 != row2 and col1 != col2:
        col1, col2 = col2, col1
    elif row1 != row2:
        row1, row2 = (row1 + 7) % 8, (row2 + 7) % 8
    else:
        col1, col2 = (col1 + 7) % 8, (col2 + 7) % 8
    decoded_flag += table[row1 * 8 + col1] + table[row2 * 8 + col2]
print(decoded_flag.replace('X', ''))
# fafalua


写作 lua，实则发现是 AngelScript 语言的玩意，找到官方仓库看源码，发现 samples 里面有个 games 和这个程序的 games 一模一样，除了游戏过关后多一个输入 check flag，以及.as 被编译为 asc，后缀改成 flua


游戏本身没有用，改 zf 过掉即可


然后会输入，输入的 flag 会过一个 gift，映射一下


打入符号表，asCContext::ExecuteNext 函数会执行 asc 的 opcode，这里猜测加密逻辑均在该函数中执行（调试非 asc 程序时会发现直接返回 no~ 并打印）


直接对该函数的 vm 分发进行批量 hook，会发现一直在执行这部分的 xor，hook 并打印，


经过调试发现这里只做了 xor，发现在对 flag 处理中不会触发其他 xor，且 xor 数量刚好为输入长度两倍


第一次 xor 中内存里看见 deadbeef 字符串，经过调试以及猜测发现是 rc4


然后跟进调试 hook，发现了另一个置换异或操作，数量恰好为 0x26


均打印 hook 结果分析，猜测加密逻辑


得到解密脚本


from Crypto.Cipher import ARC4
# print(get_reg_value('edx')," ^ ",idc.get_wide_word(get_reg_value('rax')),' = ',get_reg_value('edx') ^ idc.get_wide_word(get_reg_value('rax')))
enc_idx = [0x27, 0xfd, 0x94, 0x28, 0x97, 0x7d, 0xcb, 0xd3, 0x31, 0xdd, 0xe, 0xcc, 0x97, 0xc9, 0xa8, 0x5, 0xae, 0xaf, 0x61, 0xd0, 0x88, 0xf8, 0xd7, 0xee, 0x16, 0x36, 0x67, 0x3a, 0x8c, 0x35, 0x97, 0x2c, 0x22, 0x17, 0xdd, 0xef, 0x9a, 0x96]
for i in range(0x25, -1, -1):
    enc_idx[i] ^= enc_idx[0x26 - i - 1]
table1 = [0x63, 0x7C, 0x77, 0x7B, 0xF2, 0x6B, 0x6F, 0xC5, 0x30, 0x01, 0x67, 0x2B, 0xFE, 0xD7, 0xAB, 0x76, 0xCA, 0x82, 0xC9, 0x7D, 0xFA, 0x59, 0x47, 0xF0, 0xAD, 0xD4, 0xA2, 0xAF, 0x9C, 0xA4, 0x72, 0xC0, 0xB7, 0xFD, 0x93, 0x26, 0x36, 0x3F, 0xF7, 0xCC, 0x34, 0xA5, 0xE5, 0xF1, 0x71, 0xD8, 0x31, 0x15, 0x04, 0xC7, 0x23, 0xC3, 0x18, 0x96, 0x05, 0x9A, 0x07, 0x12, 0x80, 0xE2, 0xEB, 0x27, 0xB2, 0x75, 0x09, 0x83, 0x2C, 0x1A, 0x1B, 0x6E, 0x5A, 0xA0, 0x52, 0x3B, 0xD6, 0xB3, 0x29, 0xE3, 0x2F, 0x84, 0x53, 0xD1, 0x00, 0xED, 0x20, 0xFC, 0xB1, 0x5B, 0x6A, 0xCB, 0xBE, 0x39, 0x4A, 0x4C, 0x58, 0xCF, 0xD0, 0xEF, 0xAA, 0xFB, 0x43, 0x4D, 0x33, 0x85, 0x45, 0xF9, 0x02, 0x7F, 0x50, 0x3C, 0x9F, 0xA8, 0x51, 0xA3, 0x40, 0x8F, 0x92, 0x9D, 0x38, 0xF5, 0xBC, 0xB6, 0xDA, 0x21, 0x10, 0xFF, 0xF3, 0xD2, 0xCD, 0x0C, 0x13, 0xEC, 0x5F, 0x97, 0x44, 0x17, 0xC4, 0xA7, 0x7E, 0x3D, 0x64, 0x5D, 0x19, 0x73, 0x60, 0x81, 0x4F, 0xDC, 0x22, 0x2A, 0x90, 0x88, 0x46, 0xEE, 0xB8, 0x14, 0xDE, 0x5E, 0x0B, 0xDB, 0xE0, 0x32, 0x3A, 0x0A, 0x49, 0x06, 0x24, 0x5C, 0xC2, 0xD3, 0xAC, 0x62, 0x91, 0x95, 0xE4, 0x79, 0xE7, 0xC8, 0x37, 0x6D, 0x8D, 0xD5, 0x4E, 0xA9, 0x6C, 0x56, 0xF4, 0xEA, 0x65, 0x7A, 0xAE, 0x08, 0xBA, 0x78, 0x25, 0x2E, 0x1C, 0xA6, 0xB4, 0xC6, 0xE8, 0xDD, 0x74, 0x1F, 0x4B, 0xBD, 0x8B, 0x8A, 0x70, 0x3E, 0xB5, 0x66, 0x48, 0x03, 0xF6, 0x0E, 0x61, 0x35, 0x57, 0xB9, 0x86, 0xC1, 0x1D, 0x9E, 0xE1, 0xF8, 0x98, 0x11, 0x69, 0xD9, 0x8E, 0x94, 0x9B, 0x1E, 0x87, 0xE9, 0xCE, 0x55, 0x28, 0xDF, 0x8C, 0xA1, 0x89, 0x0D, 0xBF, 0xE6, 0x42, 0x68, 0x41, 0x99, 0x2D, 0x0F, 0xB0, 0x54, 0xBB, 0x16]
enc = []
for b in enc_idx:
    enc.append(table1.index(b))
rc4 = ARC4.new(key=b'deadbeef')
dec = rc4.decrypt(bytes(enc)).decode('utf-8')
table2 = 'abcdefghijklmnopqrstuvwxyz0123456789+/ABCDEFGHIJKLMNOPQRSTUVWXYZ'
table3 = [0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x3E, 0xFF, 0xFF, 0xFF, 0x3F, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3A, 0x3B, 0x3C, 0x3D, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x0E, 0x0F, 0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0x1A, 0x1B, 0x1C, 0x1D, 0x1E, 0x1F, 0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28, 0x29, 0x2A, 0x2B, 0x2C, 0x2D, 0x2E, 0x2F, 0x30, 0x31, 0x32, 0x33, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xC0, 0xDF, 0x1E, 0x40, 0x01, 0x00, 0x00, 0x00]
flag = ''
for m in dec:
    if m in table2:
        flag += chr(table3.index(table2.index(m)))
        # flag += m
    else:
        flag += m
print(flag)