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HTB/challenges/reversing/Simple Encryptor/rev_simpleencryptor/ape.c

@@ -0,0 +1,68 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+int encrypt(char a, int r1, int r2){
+    int t;
+    r1 = r1 & 0xff;
+    r2 = r2 & 7;
+    printf("encrypt(%x, %x, %x)\n",a,r1,r2);
+    t = a ^ r1;
+    printf("t: %x\n",t);
+    return ((t << r2)|(t >> (8-r2)));
+}
+
+int decrypt(int a, int r1, int r2){
+    int t;
+    r1 = r1 & 0xff;
+    r2 = r2 & 7;
+    a = a&0xff;
+    // printf("decrypt(%x, %x, %x)\n",a,r1,r2);
+    t = ((a << (8-r2))|(a >>r2)) & 0xff;
+    // printf("t: %x\n",t);
+    return t ^ r1;
+}
+
+int main(void) {
+    uint seed;
+    int r1,r2, enc, dec;
+    FILE *enc_file;
+    size_t size;
+
+    // seed = 0x63d17786;
+    // srand(seed);
+    // r1 = rand();
+    // r2 = rand();
+    // //printf("%x", r);
+    enc_file = fopen("flag.enc.bak","rb");
+    fseek(enc_file,0L,SEEK_END);
+    size = ftell(enc_file)-4;
+    char buffer[size+1];
+    printf("size: %x\n", size);
+    fseek(enc_file,0L,SEEK_SET);
+    fread(&seed, 4, 1, enc_file);
+    srand(seed);
+    printf("seed: %x\n", seed);
+    // buffer = malloc(2);
+    // fseek(enc_file, 0, SEEK_END);
+    // size = ftell(enc_file);
+    // fseek(enc_file, sizeof(seed), SEEK_SET);
+        // fread(buffer, 1, 1, enc_file);
+    fread(&buffer, size, 1, enc_file);
+    fclose(enc_file);
+    printf("buffer: ");
+    for (int i = 0; i < size; i++){
+        printf("%2x",buffer[i]&0xff);
+    }
+    printf("\n");
+    for (int i = 0; i < size; i++){
+
+        r1 = rand();
+        r2 = rand();
+        // // enc = encrypt('A',r1,r2);
+        // // printf("enc: %x\n", enc);
+
+        dec = decrypt(buffer[i],r1,r2);
+        printf("%c", dec);
+    }
+    return 0;
+}

HTB/challenges/reversing/Simple Encryptor/rev_simpleencryptor/ape.py

@@ -0,0 +1,7 @@
+from ctypes import *
+cdll.LoadLibrary("libc.so.6")
+libc = CDLL("libc.so.6")
+seed = 0x62b1355a
+libc.srand(seed)
+print(hex(libc.rand()&0xff))
+print(hex(libc.rand()&0x7))

HTB/challenges/reversing/Simple Encryptor/rev_simpleencryptor/decrypt.py

@@ -0,0 +1,34 @@
+import struct
+
+# Open the file for reading in binary mode
+with open("flag.enc", "rb") as f:
+    # Read the first 4 bytes, which represent the seed
+    seed_bytes = f.read(4)
+    # Unpack the seed as a 32-bit unsigned integer
+    seed = struct.unpack("I", seed_bytes)[0]
+    # Read the rest of the file contents
+    enc_data = f.read()
+
+print(f"seed: {seed}, hex: {hex(seed)}")
+print(f"enc_data: {enc_data}")
+
+# Use the seed to seed the random number generator
+import random
+random.seed(seed)
+
+# Allocate a buffer for the decrypted data
+dec_data = bytearray(len(enc_data))
+
+# Perform the decryption
+for i in range(len(enc_data)):
+    # XOR with a random byte
+    dec_data[i] = enc_data[i] ^ random.getrandbits(8)
+    # Perform the inverse bit-shift operation
+    shift = random.randint(0,7)
+    dec_data[i] = ((dec_data[i] >> shift) | (dec_data[i] << (8 - shift))) % 256
+
+print(f"flag: {dec_data}")
+
+# Write the decrypted data to a file
+# with open("flag.dec", "wb") as f:
+#     f.write(dec_data)

HTB/challenges/reversing/Simple Encryptor/rev_simpleencryptor/flag

@@ -0,0 +1 @@
+ABCD

HTB/challenges/reversing/Simple Encryptor/rev_simpleencryptor/flag.dec

@@ -0,0 +1 @@
+D:]=KN錝 <20><11>ﾂｻcｬ*<2A>ﾑ/rdj･<

HTB/challenges/reversing/Simple Encryptor/rev_simpleencryptor/flag.enc

@@ -0,0 +1 @@
+
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