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realazizk/hard.c

Created September 2, 2024 10:50
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bhmea quals rev
Raw
hard.c
/*
1. unpack Jscript code
2. brute force random key
*/
#include <windows.h>
#include <wincrypt.h>
#include <stdio.h>
#include <stdlib.h>
#include <iostream>
#include <string>
#include <iomanip>
#define MD5_DIGEST_LENGTH 16
#define AES_BLOCK_SIZE 16
void PrintHex(BYTE* data, DWORD dataLen) {
for (DWORD i = 0; i < dataLen; i++) {
printf("%02x", data[i]);
}
printf("\n");
}
void PrintErrorMessage(DWORD dwError)
{
char* messageBuffer = NULL;
FormatMessageA(
FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS,
NULL,
dwError,
MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
(LPSTR)&messageBuffer,
0,
NULL
);
if (messageBuffer != NULL)
{
printf("Error: %s\n", messageBuffer);
LocalFree(messageBuffer);
}
else
{
printf("Error code: %d\n", dwError);
}
}
int main() {
HCRYPTPROV hProv = 0;
HCRYPTHASH hHash = 0;
HCRYPTKEY hKey = 0;
BYTE ciphertext[] = {
0x73, 0xE3, 0x67, 0x95, 0x07, 0xCC, 0x81, 0x97, 0xF6, 0x65, 0xFD, 0x5B, 0x46, 0xF5, 0x53, 0x21,
0xCF, 0x89, 0xBB, 0x82, 0x8C, 0xD7, 0xBB, 0x42, 0x4B, 0x18, 0x17, 0x34, 0xD4, 0x68, 0x70, 0x97,
0x09, 0xD4, 0x90, 0x85, 0x86, 0x8C, 0xDA, 0x1B, 0x98, 0x92, 0xB9, 0x47, 0x99, 0x9E, 0x4F, 0x64
};
DWORD cipherLen = sizeof(ciphertext);
BYTE* plaintext = NULL;
DWORD plaintextLen = cipherLen;
char pbData[9];
const char* expectedPrefix = "BHFlagY";
size_t expectedPrefixLen = strlen(expectedPrefix);
if (!CryptAcquireContextA(&hProv, NULL, MS_ENH_RSA_AES_PROV_A, PROV_RSA_AES, 0)) {
PrintErrorMessage(GetLastError());
return 1;
}
for (int i = 0; i <= 99999999; i++) {
sprintf_s(pbData, "%08d", i);
if (!CryptCreateHash(hProv, CALG_MD5, 0, 0, &hHash)) {
PrintErrorMessage(GetLastError());
CryptReleaseContext(hProv, 0);
return 1;
}
if (!CryptHashData(hHash, (BYTE*)pbData, 8, 0)) {
PrintErrorMessage(GetLastError());
CryptDestroyHash(hHash);
continue;
}
if (!CryptDeriveKey(hProv, CALG_AES_128, hHash, 0, &hKey)) {
PrintErrorMessage(GetLastError());
CryptDestroyHash(hHash);
continue;
}
plaintext = (BYTE*)malloc(plaintextLen);
if (!plaintext) {
printf("Memory allocation failed\n");
CryptDestroyKey(hKey);
CryptDestroyHash(hHash);
CryptReleaseContext(hProv, 0);
return 1;
}
memcpy(plaintext, ciphertext, cipherLen);
DWORD tempLen = plaintextLen;
if (CryptDecrypt(hKey, 0, TRUE, 0, plaintext, &tempLen)) {
if (tempLen >= expectedPrefixLen && memcmp(plaintext, expectedPrefix, expectedPrefixLen) == 0) {
printf("Possible key: %s\n", pbData);
printf("Decrypted data: ");
PrintHex(plaintext, tempLen);
printf("As text: %.*s\n", tempLen, plaintext);
free(plaintext);
break;
}
}
free(plaintext);
CryptDestroyKey(hKey);
CryptDestroyHash(hHash);
}
CryptReleaseContext(hProv, 0);
return 0;
}
Raw
med.py
"""
1. unpack using binwalk
2. decompress zlib files
3. readRDS the files will print decompiled bytecode in R studio
4. solve constraints with z3
"""
"""
function ()
{
if (exists("flag", envir = .GlobalEnv)) {
flag_value <- get("flag", envir = .GlobalEnv)
if (is.character(flag_value)) {
xor_key <- "BHMEAISTHEBESTCTFEVERBETTERTHANALLOFTHEOTHERCTF"
key_length <- nchar(xor_key)
flag_length <- nchar(flag_value)
if (flag_length != key_length) {
xor_key <- substr(rep(xor_key, length.out = ceiling(flag_length/key_length)),
1, flag_length)
}
xor_result <- sapply(1:flag_length, function(i) {
flag_char <- substr(flag_value, i, i)
key_char <- substr(xor_key, i, i)
int_val <- as.integer(charToRaw(flag_char))
xor_val <- as.integer(charToRaw(key_char))
xored_val <- bitwXor(int_val, xor_val)
as.raw(xored_val)
})
return(paste0(xor_result, collapse = ""))
}
}
else {
system("echo 'try better next time'")
}
}
function ()
{
flag <- get_flag_or_die()
x <- 9
delayedAssign("y", x)
x <- x * (x - 5 + 4 + 6 - 3 - 2 - 3 - 6)
as.integer(substr(flag, 1, 1)) == y
}
"""
import z3
# Create a solver
solver = z3.Solver()
# Create a string of 94 characters (assuming the flag length is 94 based on the constraints)
flag = [z3.BitVec(f"flag_{i + 1}", 32) for i in range(94)]
flag = [None, *flag]
def substr(x, y):
z = 0
m = 1
for i in list(range(x, y + 1))[::-1]:
z += flag[i] * m
m *= 10
return z
# Add constraints for printable ASCII characters
for char in flag:
if char is None:
continue
# check hexadicmal range
solver.add(char >= 0, char <= 0xF)
pass
"""
function ()
{
flag <- get_flag_or_die()
val_1 <- as.integer(substr(flag, 51, 51))
val_2 <- as.integer(substr(flag, 22, 22))
(val_1 - val_2) == 1
}
"""
solver.add(substr(51, 51) - substr(22, 22) == 1)
"""
function ()
{
flag <- get_flag_or_die()
val_1 <- substr(flag, 14, 14)
val_2 <- substr(flag, 18, 18)
val_3 <- substr(flag, 24, 24)
val_4 <- substr(flag, 32, 32)
val_5 <- substr(flag, 36, 36)
val_6 <- substr(flag, 62, 62)
(val_1 == val_2) & (val_1 == "a") & (val_1 == val_3) & (val_3 ==
val_4) & (val_5 == val_4) & (val_6 == val_5)
}
"""
solver.add(substr(14, 14) == substr(18, 18))
solver.add(substr(14, 14) == 0xA)
solver.add(substr(14, 14) == substr(24, 24))
solver.add(substr(24, 24) == substr(32, 32))
solver.add(substr(36, 36) == substr(32, 32))
solver.add(substr(62, 62) == substr(36, 36))
"""
function ()
{
flag <- get_flag_or_die()
val_1 <- substr(flag, 16, 16)
val_2 <- substr(flag, 30, 30)
(val_1 == val_2) & (val_1 == "f")
}
"""
solver.add(substr(16, 16) == substr(30, 30))
solver.add(substr(16, 16) == 0xF)
"""
function ()
{
flag <- get_flag_or_die()
val_1 <- substr(flag, 51, 51)
val_2 <- substr(flag, 59, 59)
val_3 <- substr(flag, 63, 63)
val_4 <- substr(flag, 65, 65)
val_5 <- substr(flag, 77, 77)
val_6 <- substr(flag, 91, 91)
(val_1 == val_2) & (val_1 == val_3) & (val_1 == val_4) &
(val_1 == val_5) & (val_1 == val_6)
}
"""
solver.add(substr(51, 51) == substr(59, 59))
solver.add(substr(51, 51) == substr(63, 63))
solver.add(substr(51, 51) == substr(65, 65))
solver.add(substr(51, 51) == substr(77, 77))
solver.add(substr(51, 51) == substr(91, 91))
"""
function ()
{
flag <- get_flag_or_die()
val_1 <- substr(flag, 54, 54)
val_2 <- substr(flag, 84, 84)
val_3 <- substr(flag, 12, 12)
(val_1 == val_2) & (val_1 == "e") & (val_1 == val_3)
}
"""
solver.add(substr(54, 54) == substr(84, 84))
solver.add(substr(54, 54) == 0xE)
solver.add(substr(84, 84) == substr(12, 12))
"""
function ()
{
flag <- get_flag_or_die()
val_1 <- substr(flag, 72, 72)
val_2 <- substr(flag, 92, 92)
val_3 <- substr(flag, 26, 26)
val_4 <- substr(flag, 34, 34)
val_5 <- substr(flag, 60, 60)
(val_1 == val_2) & (val_1 == val_3) & (val_1 == val_4) &
(val_1 == val_5)
}
"""
solver.add(substr(72, 72) == substr(92, 92))
solver.add(substr(72, 72) == substr(26, 26))
solver.add(substr(72, 72) == substr(34, 34))
solver.add(substr(72, 72) == substr(60, 60))
"""
function ()
{
flag <- get_flag_or_die()
val_1 <- substr(flag, 17, 17)
val_2 <- substr(flag, 23, 23)
val_3 <- substr(flag, 28, 28)
val_4 <- substr(flag, 35, 35)
val_5 <- substr(flag, 37, 37)
val_6 <- substr(flag, 43, 43)
val_7 <- substr(flag, 44, 44)
val_8 <- substr(flag, 52, 52)
val_9 <- substr(flag, 69, 69)
val_10 <- substr(flag, 74, 74)
(val_1 == val_2) & (val_1 == val_3) & (val_1 == val_4) &
(val_1 == val_5) & (val_1 == val_6) & (val_1 == val_7) &
(val_1 == val_8) & (val_1 == val_9) & (val_1 == val_10)
}
"""
solver.add(substr(17, 17) == substr(23, 23))
solver.add(substr(17, 17) == substr(28, 28))
solver.add(substr(17, 17) == substr(35, 35))
solver.add(substr(17, 17) == substr(37, 37))
solver.add(substr(17, 17) == substr(43, 43))
solver.add(substr(17, 17) == substr(44, 44))
solver.add(substr(17, 17) == substr(52, 52))
solver.add(substr(17, 17) == substr(69, 69))
solver.add(substr(17, 17) == substr(74, 74))
"""
function ()
{
flag <- get_flag_or_die()
val_1 <- substr(flag, 22, 22)
val_2 <- substr(flag, 48, 48)
val_3 <- substr(flag, 78, 78)
val_4 <- substr(flag, 89, 89)
(val_1 == val_2) & (val_1 == val_3) & (val_1 == val_4)
}
"""
solver.add(substr(22, 22) == substr(48, 48))
solver.add(substr(22, 22) == substr(78, 78))
solver.add(substr(22, 22) == substr(89, 89))
"""
function ()
{
flag <- get_flag_or_die()
val_1 <- as.integer(substr(flag, 17, 17))
val_2 <- as.integer(substr(flag, 87, 87))
(val_1 - val_2) == -2
}
"""
solver.add(substr(17, 17) - substr(87, 87) == -2)
"""
function check_val_11(index, val)
{
flag <- get_flag_or_die()
val_1 <- substr(flag, index, index)
val_1 == val
}
check_val_11(76, "8") &
check_val_11(93, "3") &
check_val_11(13, "0") &
check_val_11(26, "5") &
check_val_11(87, "3") &
check_val_11(88, "c") &
check_val_11(81, "0") &
check_val_11(86, "0") &
check_val_11(17, "1") &
check_val_11(18, "a") &
check_val_11(19, "2") &
check_val_11(20, "b") &
check_val_11(31, "3") &
check_val_11(44, "1") &
check_val_11(49, "3") &
check_val_11(55, "3") &
check_val_11(44, "1") &
check_val_11(45, "2") &
check_val_11(39, "2") &
check_val_11(58, "2") &
check_val_11(66, "c")
"""
solver.add(substr(76, 76) == 0x8)
solver.add(substr(93, 93) == 0x3)
solver.add(substr(13, 13) == 0x0)
solver.add(substr(26, 26) == 0x5)
solver.add(substr(87, 87) == 0x3)
solver.add(substr(88, 88) == 0xC)
solver.add(substr(81, 81) == 0x0)
solver.add(substr(86, 86) == 0x0)
solver.add(substr(17, 17) == 0x1)
solver.add(substr(18, 18) == 0xA)
solver.add(substr(19, 19) == 0x2)
solver.add(substr(20, 20) == 0xB)
solver.add(substr(31, 31) == 0x3)
solver.add(substr(44, 44) == 0x1)
solver.add(substr(49, 49) == 0x3)
solver.add(substr(55, 55) == 0x3)
solver.add(substr(44, 44) == 0x1)
solver.add(substr(45, 45) == 0x2)
solver.add(substr(39, 39) == 0x2)
solver.add(substr(58, 58) == 0x2)
solver.add(substr(66, 66) == 0xC)
"""
(substr(get_flag_or_die(), 6, 6) == "b") &
"""
solver.add(substr(6, 6) == 0xB)
"""
function ()
{
flag <- get_flag_or_die()
val_1 <- as.integer(substr(flag, 7, 8))
val_2 <- as.integer(substr(flag, 9, 10))
val_3 <- as.integer(substr(flag, 89, 91))
val_4 <- as.integer(substr(flag, 92, 93))
((val_1 - val_2) == 9) & ((val_3 + val_4) == 680)
}
"""
solver.add((substr(7, 8) - substr(9, 10)) == 9)
solver.add((substr(89, 91) + substr(92, 93)) == 680)
"""
function ()
{
flag <- get_flag_or_die()
as.integer(substr(flag, 7, 11)) == 29202
}
"""
solver.add(substr(7, 11) == 29202)
"""
function ()
{
flag <- get_flag_or_die()
as.integer(substr(flag, 25, 29)) == 25213
}
"""
solver.add(substr(25, 29) == 25213)
"""
function check_val_6(index_0, index_1, val)
{
flag <- get_flag_or_die()
as.integer(substr(flag, index_0, index_1)) == val
}
check_val_6(67, 71, 22103) &
check_val_6(72, 76, 50138) &
check_val_6(37, 41, 19230) &
check_val_6(43, 47, 11202) &
"""
solver.add(substr(67, 71) == 22103)
solver.add(substr(72, 76) == 50138)
solver.add(substr(37, 41) == 19230)
solver.add(substr(43, 47) == 11202)
"""
check_val_6(77, 79, 763) &
check_val_6(85, 87, 303) &
check_val_6(59, 61, 753) &
check_val_6(39, 41, 230) &
check_val_6(21, 23, 361) &
check_val_6(51, 53, 713) &
check_val_6(33, 35, 351) &
check_val_6(45, 47, 202) &
check_val_6(63, 65, 707) &
"""
solver.add(substr(77, 79) == 763)
solver.add(substr(85, 87) == 303)
solver.add(substr(59, 61) == 753)
solver.add(substr(39, 41) == 230)
solver.add(substr(21, 23) == 361)
solver.add(substr(51, 53) == 713)
solver.add(substr(33, 35) == 351)
solver.add(substr(45, 47) == 202)
solver.add(substr(63, 65) == 707)
"""
function check_val_1(index_0, index_1, index_2)
{
flag <- get_flag_or_die()
first_two <- substr(flag, index_0, index_0) == substr(flag,
index_1, index_1)
second_two <- substr(flag, index_1, index_1) == substr(flag,
index_2, index_2)
final <- all(first_two, second_two)
return(final)
}
function (flag)
{
check_val_1(94, 82, 6) &
check_val_1(1, 86, 10) &
check_val_1(90, 83, 9) &
check_val_1(9, 11, 15) &
check_val_1(29, 61, 57) &
}
"""
def check_val_1(idx0, idx1, idx2):
return z3.And(
substr(idx0, idx0) == substr(idx1, idx1),
substr(idx1, idx1) == substr(idx2, idx2),
)
solver.add(check_val_1(94, 82, 6))
solver.add(check_val_1(1, 86, 10))
solver.add(check_val_1(90, 83, 9))
solver.add(check_val_1(9, 11, 15))
solver.add(check_val_1(29, 61, 57))
"""
function ()
{
flag <- get_flag_or_die()
if (nchar(flag) < 5) {
return(FALSE)
}
first_five <- substr(flag, 1, 5)
all_same <- all(strsplit(first_five, "")[[1]] == substr(flag,
1, 1))
return(all_same)
}
"""
solver.add(flag[1] == flag[2] == flag[3] == flag[4] == flag[5])
final_flag = flag[1:]
hehe = []
# Join the flag characters by two
for i in range(len(final_flag) // 2):
left = z3.Extract(4, 0, final_flag[i * 2])
right = z3.Extract(4, 0, final_flag[i * 2 + 1])
hehe.append(
(z3.ZeroExt(4, z3.Extract(4, 0, left)) << 4)
| z3.ZeroExt(4, z3.Extract(4, 0, right))
)
ff = "BHMEAISTHEBESTCTFEVERBETTERTHANALLOFTHEOTHERCTF"
chars_to_include = (
"0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ!#$%&'./:<=>?@_{}|"
)
calcs = []
for i, c in enumerate(hehe):
rezo = ord(ff[i]) ^ c
solver.add(z3.Or(*[ord(cc) == rezo for cc in chars_to_include]))
calcs.append(rezo)
solver.add(calcs[0] == ord("B"))
solver.add(calcs[1] == ord("H"))
solver.add(calcs[2] == ord("F"))
solver.add(calcs[3] == ord("l"))
solver.add(calcs[4] == ord("a"))
solver.add(calcs[5] == ord("g"))
solver.add(calcs[6] == ord("Y"))
solver.add(calcs[7] == ord("{"))
solver.add(calcs[39] == ord("r"))
solver.add(calcs[20] == ord("_"))
solver.add(calcs[33] == ord("n"))
solver.add(
z3.Or(
calcs[24] == ord("i"),
calcs[24] == ord("1"),
)
)
solver.add(
z3.Or(
calcs[27] == ord("i"),
calcs[27] == ord("1"),
)
)
# print(solver)
if solver.check() == z3.sat:
model = solver.model()
print(model)
flag_str = "".join([hex(model[flag[i]].as_long())[2:] for i in range(1, 95)])
import binascii
print("Flag found:", flag_str)
x = binascii.unhexlify(flag_str)
for i, c in enumerate(x):
print(chr(c ^ ord(ff[i])), end="")
else:
print("No solution found")
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