chains/zkvm/fhe_processor.go

// Copyright (C) 2019-2025, Lux Industries Inc. All rights reserved.
// See the file LICENSE for licensing terms.

package zkvm

import (
	"encoding/binary"
	"errors"
	"sync"

	"github.com/luxfi/log"
)

// FHEProcessor handles fully homomorphic encryption operations
type FHEProcessor struct {
	config ZConfig
	log    log.Logger

	// FHE parameters
	publicKey []byte
	evalKey   []byte

	// Processing statistics
	processCount uint64

	mu sync.RWMutex
}

// NewFHEProcessor creates a new FHE processor
func NewFHEProcessor(config ZConfig, log log.Logger) (*FHEProcessor, error) {
	if !config.EnableFHE {
		return nil, errors.New("FHE not enabled in config")
	}

	fp := &FHEProcessor{
		config: config,
		log:    log,
	}

	// Initialize FHE parameters
	if err := fp.initializeFHEParams(); err != nil {
		return nil, err
	}

	return fp, nil
}

// VerifyFHEOperations verifies FHE operations in a transaction
func (fp *FHEProcessor) VerifyFHEOperations(tx *Transaction) error {
	if tx.FHEData == nil {
		return errors.New("no FHE data in transaction")
	}

	fp.mu.Lock()
	fp.processCount++
	fp.mu.Unlock()

	// Verify circuit ID is supported
	if !fp.isCircuitSupported(tx.FHEData.CircuitID) {
		return errors.New("unsupported FHE circuit")
	}

	// Verify encrypted inputs
	if len(tx.FHEData.EncryptedInputs) == 0 {
		return errors.New("no encrypted inputs provided")
	}

	// Verify computation proof
	if len(tx.FHEData.ComputationProof) < 128 {
		return errors.New("invalid computation proof")
	}

	fp.log.Debug("FHE operations verified",
		log.String("txID", tx.ID.String()),
		log.String("circuitID", tx.FHEData.CircuitID),
		log.Int("inputCount", len(tx.FHEData.EncryptedInputs)),
	)

	return nil
}

// ProcessFHEComputation performs an FHE computation
func (fp *FHEProcessor) ProcessFHEComputation(
	circuitID string,
	encryptedInputs [][]byte,
) ([]byte, []byte, error) {
	// Stub: returns zero-filled result and proof
	encryptedResult := make([]byte, 256)
	computationProof := make([]byte, 256)

	fp.log.Debug("FHE computation processed",
		log.String("circuitID", circuitID),
		log.Int("inputCount", len(encryptedInputs)),
	)

	return encryptedResult, computationProof, nil
}

// EncryptValue encrypts a value using FHE
func (fp *FHEProcessor) EncryptValue(value uint64) ([]byte, error) {
	// Stub: encodes value in first 8 bytes (not encrypted)
	ciphertext := make([]byte, 256)
	// Encode value in first 8 bytes (insecure, just for testing)
	binary.BigEndian.PutUint64(ciphertext[:8], value)

	return ciphertext, nil
}

// DecryptValue decrypts an FHE ciphertext
func (fp *FHEProcessor) DecryptValue(ciphertext []byte, privateKey []byte) (uint64, error) {
	if len(ciphertext) < 256 {
		return 0, errors.New("invalid ciphertext length")
	}

	// Stub: reads value from first 8 bytes (not decrypting)
	value := binary.BigEndian.Uint64(ciphertext[:8])

	return value, nil
}

// AddCiphertexts performs homomorphic addition
func (fp *FHEProcessor) AddCiphertexts(ct1, ct2 []byte) ([]byte, error) {
	if len(ct1) != 256 || len(ct2) != 256 {
		return nil, errors.New("invalid ciphertext length")
	}

	// Stub: adds raw encoded values (not homomorphic)
	val1 := binary.BigEndian.Uint64(ct1[:8])
	val2 := binary.BigEndian.Uint64(ct2[:8])

	result := make([]byte, 256)
	binary.BigEndian.PutUint64(result[:8], val1+val2)

	return result, nil
}

// MultiplyCiphertext performs homomorphic multiplication by a plaintext
func (fp *FHEProcessor) MultiplyCiphertext(ct []byte, scalar uint64) ([]byte, error) {
	if len(ct) != 256 {
		return nil, errors.New("invalid ciphertext length")
	}

	// Stub: multiplies raw encoded value (not homomorphic)
	val := binary.BigEndian.Uint64(ct[:8])

	result := make([]byte, 256)
	binary.BigEndian.PutUint64(result[:8], val*scalar)

	return result, nil
}

// initializeFHEParams initializes FHE parameters
func (fp *FHEProcessor) initializeFHEParams() error {
	// Stub: generates zero-filled keys matching expected sizes
	switch fp.config.FHEScheme {
	case "BFV":
		fp.publicKey = make([]byte, 2048)
		fp.evalKey = make([]byte, 4096)
	case "CKKS":
		fp.publicKey = make([]byte, 2048)
		fp.evalKey = make([]byte, 4096)
	default:
		return errors.New("unsupported FHE scheme")
	}

	fp.log.Info("FHE parameters initialized",
		log.String("scheme", fp.config.FHEScheme),
		log.Int("securityLevel", int(fp.config.SecurityLevel)),
	)

	return nil
}

// isCircuitSupported checks if a circuit ID is supported
func (fp *FHEProcessor) isCircuitSupported(circuitID string) bool {
	supportedCircuits := []string{
		"add",
		"multiply",
		"compare",
		"range_proof",
		"balance_check",
	}

	for _, supported := range supportedCircuits {
		if circuitID == supported {
			return true
		}
	}

	return false
}

// GetStats returns FHE processing statistics
func (fp *FHEProcessor) GetStats() uint64 {
	fp.mu.RLock()
	defer fp.mu.RUnlock()
	return fp.processCount
}