1. 문제
Author:
oloL_neB
Language:
C/C++
Platform:
Unix/linux etc.
Arch:
x86-64
Size:
14.73 KB
Description
This isn't one of those cheesy beginner puzzles.
This is next-level security. I used sha-256, so it's super secure!!!
It is genuinely impressive what I've built here.
I don't think you're actually going to be able to solve this.2. 초기 분석
sha1: A4C1DB708F2F833F28D3247068FFBB043358C085
entry: 00000000000010b0
strings
> strings gothhouse
...
ENTER THE GOTH HOUSE
Speak the secret:
Access denied. The House does not recognize this signature.
Invalid sequence at node %d. The mechanism rejects you.
Access granted. You may enter.
...file
$ file gothhouse
gothhouse: ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=40cde4da5ae439eefb6dd399dd50f06066f94a7b, for GNU/Linux 3.2.0, stripped실행 결과
$ ./gothhouse
┌──────────────────────────────┐
│ ENTER THE GOTH HOUSE │
└──────────────────────────────┘
Speak the secret: 1234
Access denied. The House does not recognize this signature.3. 분석 및 풀이
__int64 __fastcall main(int a1, char **a2, char **a3)
{
_BYTE v4[7]; // [rsp+9h] [rbp-E7h] BYREF
_BYTE v5[32]; // [rsp+10h] [rbp-E0h] BYREF
char s[32]; // [rsp+30h] [rbp-C0h] BYREF
char v7[135]; // [rsp+50h] [rbp-A0h] BYREF
char v8; // [rsp+D7h] [rbp-19h]
size_t v9; // [rsp+D8h] [rbp-18h]
int k; // [rsp+E4h] [rbp-Ch]
int j; // [rsp+E8h] [rbp-8h]
unsigned int i; // [rsp+ECh] [rbp-4h]
memset(s, c: 0, n: sizeof(s));
puts(s: ::s);
puts(s: &byte_2070);
puts(s: &byte_2098);
printf(format: "Speak the secret: ");
if ( fgets(s: v7, n: 128, stream: stdin) == nullptr )
return 1;
v9 = strlen(s: v7);
if ( v9 != 0 && v7[v9 - 1] == '\n' )
v7[v9 - 1] = 0;
v9 = strlen(s: v7);
if ( v9 == 17 )
{
for ( i = 0; i <= 16; ++i )
{
v8 = v7[i];
for ( j = 0; j <= 5; ++j )
v4[j] = v8 + j;
v4[6] = 0;
SHA256(a1: v4, a2: 6, a3: v5);
for ( k = 0; k <= 31; ++k )
s[k] ^= v5[k];
if ( memcmp(s1: s, s2: &unk_4060 + 32 * i, n: 32u) != 0 )
{
printf(format: "\nInvalid sequence at node %d. The mechanism rejects you.\n", i + 1);
return 1;
}
}
puts(s: "\nAccess granted. You may enter.");
return 0;
}
else
{
puts(s: "\nAccess denied. The House does not recognize this signature.");
return 1;
}
}글자수가 17자 여야 하고 각 글자에 대해 0~5를 더한 v4를 sha256으로 해싱해서 s에 xor합니다.
라운드마다 unk_4060에 저장된 32자 각 라운드의 결과와 비교합니다.
입력이 123 이라면
49 50 51
>>>>>>>
49 >>> [49, 50, 51, 52, 53, 54] >>> H1 >>> F ^ H1 == X1
50 >>> [50, 51, 52, 53, 54, 55] >>> H2 >>> F ^ H1 ^ H2 == X2
51 >>> [51, 52, 53, 54, 55, 56] >>> H3 >>> F ^ H1 ^ H2 ^ H3 == X3
가 됩니다.
포인트는 SHA256가 적용될 대상 데이터의 공간이 작다는 것입니다.
( 길이가 짧고 연속된 6개의 문자를 가짐 )
따라서 X를 만들어내는 H를 찾는 여러 개의 부분 문제로 나눠서 풀 수 있습니다.
검증을 위해 첫 문자를 찾아보겠습니다.
첫 문자의 경우 s가 0인 상태이므로 xor 부분을 건너띄어도 됩니다.
import hashlib
X1 = bytes([0x43, 0xED, 0xEF, 0x52, 0x20, 0xAE, 0x3A, 0xD7, 0x18, 0x99,
0xCD, 0x35, 0x84, 0x52, 0xC1, 0xF0, 0xA1, 0x6A, 0xC4, 0x0B,
0xBB, 0x60, 0x97, 0x2F, 0xB3, 0xE2, 0xFD, 0xE5, 0x9F, 0x06,
0x77, 0xF0])
assert len(X1) == 32, "len(X) != 32"
# 입력 문자열 S의 각 글자 C_i는 [C_i, C_i+1, C_i+2, C_i+3, C_i+4, C_i+5]으로 바뀝니다.
for char in range(256):
data = bytes([(char + j) & 0xFF for j in range(6)])
sha256 = hashlib.sha256()
sha256.update(data)
result = sha256.digest()
print(f"[{char}] orig = {data}\thash = {result}\tgood = {X1}")
if result == X1:
print(f"found = {chr(char)}")
break 
첫 글자가 b 라는 걸 찾아냈습니다.
검증이 끝났으니 전체 코드를 작성합니다.
import hashlib
X = bytes([0x43, 0xED, 0xEF, 0x52, 0x20, 0xAE, 0x3A, 0xD7, 0x18, 0x99,
0xCD, 0x35, 0x84, 0x52, 0xC1, 0xF0, 0xA1, 0x6A, 0xC4, 0x0B,
0xBB, 0x60, 0x97, 0x2F, 0xB3, 0xE2, 0xFD, 0xE5, 0x9F, 0x06,
0x77, 0xF0, 0x10, 0xAA, 0x1A, 0xEB, 0xA6, 0x54, 0xA8, 0xBF,
0x27, 0xB8, 0x6C, 0xD0, 0xAC, 0x22, 0xE4, 0x3A, 0x86, 0x6C,
0x35, 0x38, 0x2B, 0x20, 0x4F, 0xC1, 0x21, 0xCE, 0x6B, 0x94,
0x26, 0xD6, 0x44, 0x2D, 0x09, 0x9A, 0xE9, 0x85, 0xA5, 0x03,
0x7A, 0xA3, 0x51, 0x27, 0x56, 0x66, 0xEA, 0x3B, 0xB2, 0xED,
0x7C, 0x24, 0x66, 0x40, 0xEE, 0x52, 0xCB, 0xA3, 0xB7, 0x41,
0x26, 0x08, 0x5A, 0x65, 0x1E, 0x93, 0x10, 0xAA, 0x1A, 0xEB,
0xA6, 0x54, 0xA8, 0xBF, 0x27, 0xB8, 0x6C, 0xD0, 0xAC, 0x22,
0xE4, 0x3A, 0x86, 0x6C, 0x35, 0x38, 0x2B, 0x20, 0x4F, 0xC1,
0x21, 0xCE, 0x6B, 0x94, 0x26, 0xD6, 0x44, 0x2D, 0xC7, 0xF6,
0x9B, 0x49, 0xB1, 0x3D, 0x5F, 0x67, 0xA0, 0x3E, 0x50, 0xFA,
0xA6, 0xA6, 0xF3, 0x30, 0x96, 0xFD, 0x4A, 0x54, 0xCD, 0x3B,
0x93, 0x59, 0x23, 0x94, 0x33, 0xB5, 0x87, 0xE3, 0xE2, 0x17,
0xEC, 0xD3, 0xF0, 0xC1, 0xAD, 0x3B, 0x6B, 0xEB, 0xBC, 0xA1,
0x93, 0x91, 0xE0, 0x8E, 0x0E, 0x3A, 0x65, 0xB1, 0xB3, 0x28,
0xC8, 0x15, 0x24, 0xAD, 0xA0, 0x81, 0x20, 0x58, 0x65, 0x1F,
0x1C, 0x7E, 0xD0, 0xC3, 0x6F, 0x39, 0x5E, 0x0A, 0x5C, 0x3F,
0x19, 0x70, 0x78, 0x4C, 0xA7, 0x24, 0x46, 0xEE, 0x1C, 0xB6,
0xF6, 0xD3, 0x16, 0x9F, 0x69, 0xE0, 0x28, 0xE2, 0x4E, 0xD6,
0x81, 0xCD, 0xD4, 0x85, 0x83, 0x84, 0x9A, 0x80, 0xD8, 0xF0,
0xCE, 0x57, 0x26, 0x51, 0xD9, 0xA9, 0x8F, 0x54, 0x63, 0x24,
0x3B, 0xB0, 0x07, 0xE0, 0x86, 0xDF, 0xB1, 0x0E, 0xBA, 0xCE,
0xD8, 0xA7, 0x38, 0x1D, 0xE7, 0x58, 0xC2, 0x9E, 0xEA, 0x7C,
0x0C, 0x5A, 0xA2, 0x8A, 0xD5, 0xA2, 0x74, 0x3D, 0x4E, 0xA6,
0xDA, 0xE3, 0x9F, 0x75, 0xEE, 0x0B, 0x60, 0x0C, 0x8E, 0x26,
0x0D, 0xEC, 0x9A, 0x05, 0x79, 0xB5, 0x2A, 0x75, 0xFE, 0x8E,
0x75, 0x84, 0xFF, 0x6B, 0x95, 0x5E, 0x70, 0x73, 0x9F, 0xE0,
0x09, 0x0C, 0x92, 0x37, 0xE6, 0x72, 0xAB, 0xF0, 0xBE, 0x86,
0xC3, 0x6B, 0x85, 0x8F, 0xF4, 0x8B, 0x9D, 0x67, 0xE2, 0x8E,
0x3E, 0x73, 0x25, 0x71, 0x4C, 0xB7, 0x94, 0xA3, 0xE0, 0x2E,
0xE0, 0x63, 0x75, 0xE0, 0xC9, 0xFD, 0xB4, 0x59, 0x99, 0x02,
0x57, 0x3A, 0x79, 0xD4, 0x22, 0x5B, 0xF0, 0xA3, 0xE0, 0xB8,
0x71, 0x25, 0x04, 0x0C, 0x7C, 0x01, 0x4A, 0x51, 0xC3, 0xE6,
0xE1, 0x03, 0x6A, 0x74, 0xAE, 0x48, 0x99, 0xA7, 0x7D, 0x87,
0xC0, 0x75, 0xA7, 0x37, 0x8F, 0x82, 0xE4, 0xAC, 0x8C, 0xF6,
0x94, 0x50, 0x49, 0x55, 0x45, 0x16, 0x0C, 0xFD, 0x9E, 0xFB,
0xAF, 0x3B, 0x12, 0xF0, 0xC7, 0xE0, 0x6F, 0xBA, 0x20, 0x60,
0xD9, 0x42, 0x29, 0x9E, 0x41, 0xE4, 0xB0, 0xAA, 0x53, 0x8E,
0xCE, 0x54, 0xD5, 0xF8, 0x84, 0x78, 0x76, 0x06, 0x8A, 0xB5,
0x6E, 0x6A, 0xB3, 0xA3, 0x1C, 0x72, 0x68, 0x22, 0xEC, 0x5E,
0x2E, 0xD7, 0x37, 0x77, 0x44, 0x80, 0x9B, 0xFB, 0xC3, 0x4E,
0x9A, 0x71, 0xBD, 0xE3, 0x17, 0x41, 0xFC, 0xB8, 0xC8, 0xF3,
0xF4, 0x72, 0x9B, 0x50, 0xDE, 0xE3, 0xA2, 0xC4, 0x28, 0x85,
0x6C, 0xF8, 0x17, 0x1F, 0x0C, 0xB5, 0xDE, 0x48, 0x32, 0x7A,
0xAC, 0x51, 0x5C, 0xB4, 0x7B, 0x3F, 0xCE, 0x7D, 0xBB, 0x99,
0x7C, 0x1F, 0x78, 0x42, 0x55, 0xA6, 0xEC, 0xDC, 0x39, 0x24,
0x85, 0x1E, 0x1F, 0x67, 0x83, 0x8C, 0x63, 0xBF, 0xDE, 0x3B,
0x8A, 0x44, 0xB0, 0x48, 0x89, 0xB7, 0x1D, 0x88, 0x22, 0x45,
0x64, 0x23, 0x46, 0x60, 0x21, 0x32, 0x53, 0x40, 0xBB, 0x99,
0x38, 0x09, 0x0F, 0x09, 0xC4, 0xCF, 0xD3, 0xD6, 0xAA, 0x61,
0x87, 0x4C, 0x7A, 0x49, 0x46, 0x1E, 0x4F, 0x40, 0x61, 0xDD,
0x56, 0xAD, 0x5C, 0x53])
# 글자당 32개, 17글자.
assert len(X) == 32*17, "len(X) != 32*17"
# char s[32]
F = bytearray(32)
flag = ''
for index in range(17):
print(f"solving flag[{index}]...")
for char in range(256):
# [C_i, C_i+1, C_i+2, C_i+3, C_i+4, C_i+5]
data = bytes([(char + j) & 0xFF for j in range(6)])
sha256 = hashlib.sha256()
sha256.update(data)
hash = sha256.digest()
result = bytearray(F)
# s[k] ^= v5[k];
for hash_index in range(32):
result[hash_index] ^= hash[hash_index]
start = index * 32
end = start + 32
if bytes(result) == X[start : end]:
#print(f"orig = {F}\tgood = {X[start : end]}")
found = chr(char)
print(f"found = {found}")
flag += found
F = result
break
print(f"flag = {flag}")
4. 플래그 입력
$ ./gothhouse
┌──────────────────────────────┐
│ ENTER THE GOTH HOUSE │
└──────────────────────────────┘
Speak the secret: buttercupcosplays
Access granted. You may enter.