# blank

```
Why should we trust the kernel mode Syscalls to handle the errors ?

Author : N!L
```

Writeup written by AI agent:

# Reverse Engineering CTF Challenge Solution

## Challenge Analysis

The binary is a simple reverse engineering challenge that XORs encrypted data segments with corresponding pad values to reveal a flag.

## Binary Structure

- Main function loops 10 times (NUM\_SEGMENTS = 10)
- For each iteration:
- XORs 32 bytes from `cipher_segments[i]` with `pads[i]`
- Writes result to file descriptor 5
- Reads 1 byte from file descriptor 7
- Writes "OK" to file descriptor 8

## Data Locations

- cipher\_segments: virtual address 0x4aa100, file offset 0xa9100
- pads: virtual address 0x4aa240, file offset 0xa9240
- NUM\_SEGMENTS: 10 (stored at 0x4aa0e0)

## Solution Approach

1. Extract cipher\_segments and pads arrays from the binary
2. XOR corresponding segments (`cipher[i] ^ pads[i]`)
3. Remove null bytes and decode as UTF-8
4. Concatenate all decoded segments

## Flag Extraction

The flag is revealed by XORing each 32-byte segment:

- Segment 0: `nexus{`
- Segment 1: `th3_f`
- Segment 2: `l4g_w1ll`
- Segment 3: `_r3ve4l`
- Segment 4: `_1ts3l`
- Segment 5: `f_wh3n`
- Segment 6: `_y0u_`
- Segment 7: `st0p_`
- Segment 8: `look`
- Segment 9: `1ng}`

Complete flag: nexus{th3\_fl4g\_w1ll\_r3ve4l\_1ts3lf\_wh3n\_y0u\_st0p\_look1ng}

## Testing

The binary can be tested with pipe redirection:

```
./blank 5>&1 7</dev/null 8>&1
```

This outputs the flag segments interleaved with "OK" messages.

## Tools Used

- Python for data extraction and XOR operations
- ELF analysis tools (readelf) for section mapping