bytemancy 1

Challenge Description

Can you conjure the right bytes? The program’s source code can be downloaded. (Second in the bytemancy series — basic byte/encoding manipulation)

Approach

This is the second challenge in the “bytemancy” series (following bytemancy 0 at 50 points). At 100 points with 2097 solves, it remains in the accessible range but introduces slightly more complex byte manipulation than the first level.

Key Concepts

1. Byte representation: Data can be expressed in multiple forms — decimal, hexadecimal, octal, binary, and ASCII. Converting fluently between these representations is the core skill tested.
2. Encoding schemes: Base64, hex encoding, URL encoding, and other standard transformations that convert binary data to text-safe formats.
3. Byte-level operations: XOR, bitwise AND/OR, bit shifting, nibble swapping, and modular arithmetic on individual bytes.
4. Endianness: The byte order in which multi-byte values are stored — little-endian (least significant byte first) vs. big-endian (most significant byte first).

What Differentiates bytemancy 1 from bytemancy 0

Building on the introductory bytemancy 0, this level likely introduces one or more of these additional complexities:

• Multi-step transformations: Instead of a single operation (e.g., just hex decoding), the input may need to pass through two or more transformations in sequence.
• Mixed encoding formats: The program may expect input in one format (e.g., decimal) but display targets in another (e.g., hex), requiring the solver to convert between them.
• Simple cipher operations: A single-byte XOR cipher, Caesar-style byte rotation, or byte substitution table.
• Byte ordering constraints: The correct answer may require understanding little-endian vs. big-endian packing.
• Non-printable bytes: Some required bytes may fall outside the printable ASCII range (0x20-0x7E), requiring raw byte input.

Analysis Strategy

1. Download the provided source code
2. Read it carefully to understand:
   • What input format the program expects (hex string, raw bytes, space-separated decimals, etc.)
   • What transformations are applied to the input
   • What the target/expected output is
3. Reverse the transformations to compute the required input
4. Send the correct bytes to the program to receive the flag

Solution

Step 1: Download and examine the source code

# Download the source code from the challenge page
wget <challenge_url>/bytemancy1.py
cat bytemancy1.py

Step 2: Identify the transformation logic

The source code typically contains a validation function that:

1. Reads user input
2. Applies one or more transformations
3. Compares the result to hardcoded expected values
4. Prints the flag if the comparison succeeds

Example pseudocode pattern:

expected = [0xa3, 0xf1, 0x42, ...]  # target byte values
key = 0x55                            # XOR key

user_input = read_input()             # e.g., hex string from stdin
transformed = [b ^ key for b in user_input]

if transformed == expected:
    print(flag)

Step 3: Reverse the transformation

For each type of operation, the inverse is:

Step 4: Construct and send the payload

# If the program runs locally:
python3 solve.py | python3 bytemancy1.py

# If the program runs as a remote service:
python3 solve.py | nc <host> <port>

# Or use the solve script directly:
python3 solve.py --source bytemancy1.py
python3 solve.py --host <HOST> --port <PORT>

Step 5: Capture the flag

The program validates the input and prints the flag upon success.

Solution Script

python3 solve.py

Flag

picoCTF{...}  (placeholder - actual flag varies per instance)