#!/bin/bash
# LUKS KDF configuration hook - Convert PBKDF2 to Argon2id
# Addresses FINDING-005: Argon2id KDF not explicitly configured
#
# Debian partman-crypto does not support preseed configuration for KDF type.
# Default LUKS2 uses PBKDF2. This hook creates tools for user-initiated
# conversion to Argon2id (more resistant to GPU-based attacks).
#
# Reference: PRD.md FR-001, security-model.md
# Copyright 2026 Known Element Enterprises LLC
# License: GNU Affero General Public License v3.0 only
set -euo pipefail

echo "Configuring LUKS KDF optimization tools..."

# Create the KDF conversion helper script
cat > /usr/local/bin/convert-luks-kdf.sh <<'SCRIPT'
#!/bin/bash
# Convert LUKS2 KDF from PBKDF2 to Argon2id
# Run this script with sudo after first boot
set -euo pipefail

echo "================================================================================"
echo "  KNEL-Football Secure OS - LUKS KDF Optimization"
echo "================================================================================"
echo ""
echo "This script converts your LUKS2 key derivation function to Argon2id."
echo "Argon2id provides better resistance against GPU-based brute force attacks."
echo ""
echo "You will need to enter your encryption passphrase."
echo ""

# Check root privileges
if [ "$EUID" -ne 0 ]; then
    echo "ERROR: This script must be run as root (use sudo)"
    exit 1
fi

# Find the LUKS device (typically /dev/sda3 or /dev/nvme0n1p3)
LUKS_DEVICE=""
for dev in /dev/sda3 /dev/nvme0n1p3 /dev/vda3; do
    if [ -b "$dev" ] && cryptsetup isLuks "$dev" 2>/dev/null; then
        LUKS_DEVICE="$dev"
        break
    fi
done

if [ -z "$LUKS_DEVICE" ]; then
    echo "ERROR: No LUKS device found"
    echo "Checked: /dev/sda3, /dev/nvme0n1p3, /dev/vda3"
    exit 1
fi

echo "Found LUKS device: $LUKS_DEVICE"
echo ""

# Check current KDF
CURRENT_KDF=$(cryptsetup luksDump "$LUKS_DEVICE" 2>/dev/null | grep -E "^\s+KDF:" | head -1 | awk '{print $2}' || echo "unknown")
echo "Current KDF: $CURRENT_KDF"

if [ "$CURRENT_KDF" = "argon2id" ]; then
    echo ""
    echo "SUCCESS: KDF is already configured as Argon2id"
    echo "No conversion needed."

    # Mark as done so reminder stops appearing
    touch /var/lib/knel-kdf-optimized
    exit 0
fi

echo ""
echo "Converting KDF to Argon2id..."
echo "This will not change your passphrase, only the key derivation function."
echo ""

# Convert to Argon2id
# Note: luksConvertKey requires entering the existing passphrase
if cryptsetup luksConvertKey "$LUKS_DEVICE" --pbkdf argon2id; then
    echo ""
    echo "================================================================================"
    echo "  SUCCESS: KDF converted to Argon2id"
    echo "================================================================================"
    echo ""
    echo "Your LUKS encryption now uses Argon2id key derivation function."
    echo "This provides better protection against brute force attacks."
    echo ""

    # Mark as done so reminder stops appearing
    touch /var/lib/knel-kdf-optimized

    # Verify the conversion
    NEW_KDF=$(cryptsetup luksDump "$LUKS_DEVICE" 2>/dev/null | grep -E "^\s+KDF:" | head -1 | awk '{print $2}')
    echo "Verified KDF: $NEW_KDF"
else
    echo ""
    echo "ERROR: KDF conversion failed"
    echo "This may happen if the passphrase was incorrect."
    echo "Your encryption is still working with the previous KDF."
    exit 1
fi
SCRIPT

chmod +x /usr/local/bin/convert-luks-kdf.sh

# Create login reminder for the user
cat > /etc/profile.d/knel-kdf-reminder.sh <<'REMINDER'
#!/bin/sh
# Reminder to optimize LUKS KDF (runs on login until completed)
# This file is removed/modified after KDF conversion

if [ ! -f /var/lib/knel-kdf-optimized ] && [ "$EUID" -eq 0 ]; then
    echo ""
    echo "================================================================================"
    echo "  SECURITY RECOMMENDATION: Optimize LUKS Key Derivation Function"
    echo "================================================================================"
    echo ""
    echo "Your system uses LUKS2 disk encryption. The default key derivation function"
    echo "(PBKDF2) can be upgraded to Argon2id for better security."
    echo ""
    echo "To upgrade, run:"
    echo "    sudo /usr/local/bin/convert-luks-kdf.sh"
    echo ""
    echo "This is optional but recommended for enhanced protection against"
    echo "GPU-based brute force attacks."
    echo ""
fi
REMINDER

chmod +x /etc/profile.d/knel-kdf-reminder.sh

# Update the README to reflect the actual configuration
if [ -f /var/backups/keys/README.txt ]; then
    sed -i 's/- KDF: Argon2id/- KDF: Argon2id (run \/usr\/local\/bin\/convert-luks-kdf.sh to enable)/' /var/backups/keys/README.txt 2>/dev/null || true
fi

echo "LUKS KDF optimization tools configured."
echo "Helper script: /usr/local/bin/convert-luks-kdf.sh"
echo "User reminder: /etc/profile.d/knel-kdf-reminder.sh"