REVERSE-PRACTICE-JarvisOJ-4

• • Classical Crackme
  • FindKey

Classical Crackme

exe程序，輸入注冊碼，輸入錯誤彈窗
查殼發現是.Net程序，dnSpy打開（要不要用de4dot unpack無所謂，這里打開的是解包過的程序）
按下“注冊”按鈕后的邏輯為，讀取輸入，將輸入用base64編碼，編碼結果與已知字符串比較，驗證輸入

直接解已知字符串的base64即可得到flag

FindKey

.pyc文件，uncompyle6反編譯，得到python源碼
主要的邏輯為，讀取輸入，檢驗輸入長度是否為17，輸入倒序，驗證輸入內容

import sys lookup = [196, 153, 149, 206, 17, 221, 10, 217, 167, 18, 36, 135, 103, 61, 111, 31, 92, 152, 21, 228, 105, 191, 173, 41, 2, 245, 23, 144, 1, 246, 89, 178, 182, 119, 38, 85, 48, 226, 165, 241, 166, 214, 71, 90, 151, 3, 109, 169, 150, 224, 69, 156, 158, 57, 181, 29, 200, 37, 51, 252, 227, 93, 65, 82, 66, 80, 170, 77, 49, 177, 81, 94, 202, 107, 25, 73, 148, 98, 129, 231, 212, 14, 84, 121, 174, 171, 64, 180, 233, 74, 140, 242, 75, 104, 253, 44, 39, 87, 86, 27, 68, 22, 55, 76, 35, 248, 96, 5, 56, 20, 161, 213, 238, 220, 72, 100, 247, 8, 63, 249, 145, 243, 155, 222, 122, 32, 43, 186, 0, 102, 216, 126, 15, 42, 115, 138, 240, 147, 229, 204, 117, 223, 141, 159, 131, 232, 124, 254, 60, 116, 46, 113, 79, 16, 128, 6, 251, 40, 205, 137, 199, 83, 54, 188, 19, 184, 201, 110, 255, 26, 91, 211, 132, 160, 168, 154, 185, 183, 244, 78, 33, 123, 28, 59, 12, 210, 218, 47, 163, 215, 209, 108, 235, 237, 118, 101, 24, 234, 106, 143, 88, 9, 136, 95, 30, 193, 176, 225, 198, 197, 194, 239, 134, 162, 192, 11, 70, 58, 187, 50, 67, 236, 230, 13, 99, 190, 208, 207, 7, 53, 219, 203, 62, 114, 127, 125, 164, 179, 175, 112, 172, 250, 133, 130, 52, 189, 97, 146, 34, 157, 120, 195, 45, 4, 142, 139] pwda = [188, 155, 11, 58, 251, 208, 204, 202, 150, 120, 206, 237, 114, 92, 126, 6, 42] pwdb = [53, 222, 230, 35, 67, 248, 226, 216, 17, 209, 32, 2, 181, 200, 171, 60, 108] flag = raw_input('Input your Key:').strip() if len(flag) != 17:print 'Wrong Key!!'sys.exit(1) flag = flag[::-1] for i in range(0, len(flag)):if ord(flag[i]) + pwda[i] & 255 != lookup[(i + pwdb[i])]:print 'Wrong Key!!'sys.exit(1)print 'Congratulations!!'

寫逆運算腳本即可得到flag

lookup = [196, 153, 149, 206, 17, 221, 10, 217, 167, 18, 36, 135, 103, 61, 111, 31, 92, 152, 21, 228, 105, 191, 173, 41, 2, 245, 23, 144, 1, 246, 89, 178, 182, 119, 38, 85, 48, 226, 165, 241, 166, 214, 71, 90, 151, 3, 109, 169, 150, 224, 69, 156, 158, 57, 181, 29, 200, 37, 51, 252, 227, 93, 65, 82, 66, 80, 170, 77, 49, 177, 81, 94, 202, 107, 25, 73, 148, 98, 129, 231, 212, 14, 84, 121, 174, 171, 64, 180, 233, 74, 140, 242, 75, 104, 253, 44, 39, 87, 86, 27, 68, 22, 55, 76, 35, 248, 96, 5, 56, 20, 161, 213, 238, 220, 72, 100, 247, 8, 63, 249, 145, 243, 155, 222, 122, 32, 43, 186, 0, 102, 216, 126, 15, 42, 115, 138, 240, 147, 229, 204, 117, 223, 141, 159, 131, 232, 124, 254, 60, 116, 46, 113, 79, 16, 128, 6, 251, 40, 205, 137, 199, 83, 54, 188, 19, 184, 201, 110, 255, 26, 91, 211, 132, 160, 168, 154, 185, 183, 244, 78, 33, 123, 28, 59, 12, 210, 218, 47, 163, 215, 209, 108, 235, 237, 118, 101, 24, 234, 106, 143, 88, 9, 136, 95, 30, 193, 176, 225, 198, 197, 194, 239, 134, 162, 192, 11, 70, 58, 187, 50, 67, 236, 230, 13, 99, 190, 208, 207, 7, 53, 219, 203, 62, 114, 127, 125, 164, 179, 175, 112, 172, 250, 133, 130, 52, 189, 97, 146, 34, 157, 120, 195, 45, 4, 142, 139] pwda = [188, 155, 11, 58, 251, 208, 204, 202, 150, 120, 206, 237, 114, 92, 126, 6, 42] pwdb = [53, 222, 230, 35, 67, 248, 226, 216, 17, 209, 32, 2, 181, 200, 171, 60, 108] flag=[0]*17 for i in range(len(flag)):flag[i]=lookup[i+pwdb[i]]-pwda[i]&255 flag=flag[::-1] print(''.join(chr(i) for i in flag)) #PCTF{PyC_Cr4ck3r}

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