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[原创]imaginaryCTF2021和rarCTF2021的两道非常相似的逆向题
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发表于: 2021-8-10 10:51 8288
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最近周末空闲的时候一直在玩CTF巩固基础,遇到两道很相似的逆向题,第一道解出来了,第二道没解出来,说明还是有些东西没搞懂
imaginaryCTF2021-string
此题简单明了,需要将输入的内容进行ASCII码的加减操作,编写个简单的程序就能得出flag
#include <stdio.h> #include <string.h> int main() { char *v1,*v2; v1="jdug|tus2oht`5s4ou`i2ee4o`28c32b7:~"; for(int i=0; i<=34; ++i) { v2=(v1[i]-1); printf("%s", &v2); } return 0; }
rarCTF-verybabyrev
此题和第一题一样是对数据进行操作,只不过这次是异或
import string local_108 = 0x45481d1217111313 local_100 = 0x095f422c260b4145 local_f8 = 0x541b56563d6c5f0b local_f0 = 0x585c0b3c2945415f local_e8 = 0x402a6c54095d5f00 local_e0 = 0x4b5f4248276a0606 local_d8 = 0x6c5e5d432c2d4256 local_d0 = 0x6b315e434707412d local_c8 = 0x5e54491c6e3b0a5a local_c0 = 0x2828475e05342b1a local_b8 = 0x060450073b26111f local_b0 = 0x0a774803050b0d04 blocks = [local_108, local_100, local_f8, local_f0, local_e8, local_e0, local_d8, local_d0, local_c8, local_c0, local_b8, local_b0] rawdata = b'' for b in blocks: rawdata += b.to_bytes(8, 'little') def encode(plaintext): out = b'' local_c = 0 while True: if local_c + 1 == len(plaintext): break out += (plaintext[local_c] ^ plaintext[local_c+1]).to_bytes(1, 'little') local_c += 1 return out knownpt = b'rarctf{' start = len(knownpt) for i in range(start, 0x61, 1): for j in string.printable: res = encode(knownpt + j.encode('utf-8')) if res == rawdata[:i]: knownpt += j.encode('utf-8') print('flag: %s' % knownpt.decode('utf-8'))
总结
两题虽然是逆向题但是第二题已经很接近密码学了(从解法也能看得出来),不过这两题都是ctf的逆向入门题,在此记录一下以便学习
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