ENCRYPTION.md

Monster Hunter PSP Encryption

Overview

Monster Hunter PSP games (MHP2G, MHFU, MHP3rd) use encryption on various data files. The mhef (Monster Hunter Encryption Functions) library provides tools to decrypt and encrypt these files.

Encrypted File Types

File Type	Description	Encryption
DATA.BIN	Main game archive	Data cipher
Quest files (.mib)	Quest definitions	Quest cipher
Save data	Player saves	Save cipher
DLC files	Downloaded content	DLC cipher

Data Cipher (DATA.BIN)

Used for the main DATA.BIN archive:

from mhef.psp import DataCipher

# Game-specific cipher
cipher = DataCipher(DataCipher.MHP2G)  # For MHFU/MHP2G
# cipher = DataCipher(DataCipher.MHP3)  # For MHP3rd

# Decrypt
with open('DATA.BIN', 'rb') as f:
    encrypted = f.read()
decrypted = cipher.decrypt(encrypted)

# Encrypt
encrypted = cipher.encrypt(decrypted)

Quest Cipher

Used for quest/mission files:

from mhef.psp import QuestCipher

cipher = QuestCipher(QuestCipher.MHP2G)

# Decrypt quest file
decrypted = cipher.decrypt(encrypted_quest)

# Encrypt quest file
encrypted = cipher.encrypt(decrypted_quest)

Save Cipher

Used for save game data:

from mhef.psp import SaveCipher

cipher = SaveCipher(SaveCipher.MHP2G)

# Decrypt save
decrypted = cipher.decrypt(encrypted_save)

# Encrypt save
encrypted = cipher.encrypt(decrypted_save)

DLC Cipher

Used for downloaded content:

from mhef.psp import DLCCipher

cipher = DLCCipher(DLCCipher.MHP2G)

# Decrypt DLC
decrypted = cipher.decrypt(encrypted_dlc)

# Encrypt DLC
encrypted = cipher.encrypt(decrypted_dlc)

Cipher Implementations

Technical Details

The encryption uses a combination of:

• XOR operations with key tables
• Byte shuffling/permutation
• Block-based processing

The key tables are derived from game-specific seeds and vary by:

• Game version (MHP2G vs MHP3)
• File type (data vs quest vs save)
• Region (JP vs NA vs EU)

Key Table Generation

# Pseudocode for key table generation
def generate_key_table(seed, size):
    table = bytearray(size)
    state = seed

    for i in range(size):
        state = (state * MULTIPLIER + INCREMENT) & 0xFFFFFFFF
        table[i] = (state >> 16) & 0xFF

    return table

Region Differences

Different game regions may use different encryption keys:

Game	Region	Notes
MHP2G	JP	Original Japanese release
MHFU	NA	North American release
MHFU	EU	European release

FUComplete handles cross-region saves by supporting all key variants.

Command Line Usage

mhef includes command-line tools:

# Decrypt DATA.BIN
python -m mhef.psp.data decrypt MHP2G DATA.BIN DATA_decrypted.BIN

# Encrypt DATA.BIN
python -m mhef.psp.data encrypt MHP2G DATA_decrypted.BIN DATA.BIN

# Decrypt quest
python -m mhef.psp.quest decrypt MHP2G quest.mib quest_decrypted.mib

Integration with Other Tools

FUComplete Workflow

1. Extract ISO to get DATA.BIN
2. Decrypt DATA.BIN using mhef
3. Modify files
4. Re-encrypt DATA.BIN
5. Replace in ISO

UMD-Replace

Used after encryption to replace DATA.BIN in the ISO without full rebuild.

Dependencies

mhef requires:

• Python 3.x
• PyCrypto or PyCryptodome

pip install pycryptodome
pip install mhef

References

• mhef library: https://github.com/svanheulen/mhef
• GitLab mirror: https://gitlab.com/svanheulen/mhef