crypto/mlkem/mlkem_placeholder.go.bak

// Copyright (C) 2025, Lux Industries Inc. All rights reserved.
// Package mlkem provides ML-KEM (FIPS 203) key encapsulation mechanism
// This is a placeholder implementation for CI testing

package mlkem

import (
	"crypto/sha256"
	"errors"
	"io"
)

// Security parameters for ML-KEM (Module Lattice Key Encapsulation Mechanism)
const (
	// ML-KEM-512 (Level 1 security)
	MLKEM512PublicKeySize    = 800
	MLKEM512PrivateKeySize   = 1632
	MLKEM512CiphertextSize   = 768
	MLKEM512SharedSecretSize = 32

	// ML-KEM-768 (Level 3 security)
	MLKEM768PublicKeySize    = 1184
	MLKEM768PrivateKeySize   = 2400
	MLKEM768CiphertextSize   = 1088
	MLKEM768SharedSecretSize = 32

	// ML-KEM-1024 (Level 5 security)
	MLKEM1024PublicKeySize    = 1568
	MLKEM1024PrivateKeySize   = 3168
	MLKEM1024CiphertextSize   = 1568
	MLKEM1024SharedSecretSize = 32
)

// Mode represents the ML-KEM parameter set
type Mode int

const (
	MLKEM512 Mode = iota + 1
	MLKEM768
	MLKEM1024
)

// PublicKey represents an ML-KEM public key
type PublicKey struct {
	mode Mode
	data []byte
}

// PrivateKey represents an ML-KEM private key
type PrivateKey struct {
	PublicKey PublicKey
	data      []byte
}

// EncapsulationResult contains the ciphertext and shared secret
type EncapsulationResult struct {
	Ciphertext   []byte
	SharedSecret []byte
}

// GenerateKeyPair generates a new ML-KEM key pair
func GenerateKeyPair(rand io.Reader, mode Mode) (*PrivateKey, error) {
	var pubKeySize, privKeySize int

	switch mode {
	case MLKEM512:
		pubKeySize = MLKEM512PublicKeySize
		privKeySize = MLKEM512PrivateKeySize
	case MLKEM768:
		pubKeySize = MLKEM768PublicKeySize
		privKeySize = MLKEM768PrivateKeySize
	case MLKEM1024:
		pubKeySize = MLKEM1024PublicKeySize
		privKeySize = MLKEM1024PrivateKeySize
	default:
		return nil, errors.New("invalid ML-KEM mode")
	}

	// Check for nil random source
	if rand == nil {
		return nil, errors.New("random source is nil")
	}
	
	// Placeholder implementation - generate random private key
	privBytes := make([]byte, privKeySize)
	if _, err := io.ReadFull(rand, privBytes); err != nil {
		return nil, err
	}

	// Derive public key from private key deterministically
	h := sha256.New()
	h.Write(privBytes[:32]) // Use first 32 bytes as seed
	h.Write([]byte("public"))
	pubSeed := h.Sum(nil)

	pubBytes := make([]byte, pubKeySize)
	// Fill public key with deterministic data
	for i := 0; i < pubKeySize; i += 32 {
		h.Reset()
		h.Write(pubSeed)
		h.Write([]byte{byte(i / 32)})
		hash := h.Sum(nil)
		end := i + 32
		if end > pubKeySize {
			end = pubKeySize
		}
		copy(pubBytes[i:end], hash)
	}

	return &PrivateKey{
		PublicKey: PublicKey{
			mode: mode,
			data: pubBytes,
		},
		data: privBytes,
	}, nil
}

// Encapsulate generates a shared secret and ciphertext
func (pub *PublicKey) Encapsulate(rand io.Reader) (*EncapsulationResult, error) {
	if pub == nil {
		return nil, errors.New("public key is nil")
	}
	
	var ctSize int

	switch pub.mode {
	case MLKEM512:
		ctSize = MLKEM512CiphertextSize
	case MLKEM768:
		ctSize = MLKEM768CiphertextSize
	case MLKEM1024:
		ctSize = MLKEM1024CiphertextSize
	default:
		return nil, errors.New("invalid ML-KEM mode")
	}

	// Placeholder: generate random ciphertext
	ct := make([]byte, ctSize)
	if _, err := io.ReadFull(rand, ct); err != nil {
		return nil, err
	}

	// Placeholder: derive shared secret deterministically
	// Use SHA256(pubkey || ciphertext) for consistency
	h := sha256.New()
	h.Write(pub.data)
	h.Write(ct)
	ss := h.Sum(nil)

	// Store the ciphertext hash for later decapsulation
	// In real implementation, this would be proper KEM

	return &EncapsulationResult{
		Ciphertext:   ct,
		SharedSecret: ss,
	}, nil
}

// Decapsulate recovers the shared secret from ciphertext
func (priv *PrivateKey) Decapsulate(ciphertext []byte) ([]byte, error) {
	if priv == nil {
		return nil, errors.New("private key is nil")
	}
	
	var expectedCtSize int

	switch priv.PublicKey.mode {
	case MLKEM512:
		expectedCtSize = MLKEM512CiphertextSize
	case MLKEM768:
		expectedCtSize = MLKEM768CiphertextSize
	case MLKEM1024:
		expectedCtSize = MLKEM1024CiphertextSize
	default:
		return nil, errors.New("invalid ML-KEM mode")
	}

	if len(ciphertext) != expectedCtSize {
		return nil, errors.New("invalid ciphertext size")
	}

	// Placeholder: derive shared secret deterministically
	// Use same formula as Encapsulate: SHA256(pubkey || ciphertext)
	// This ensures matching shared secrets
	h := sha256.New()
	h.Write(priv.PublicKey.data)
	h.Write(ciphertext)
	ss := h.Sum(nil)

	return ss, nil
}

// Bytes returns the public key as bytes
func (pub *PublicKey) Bytes() []byte {
	return pub.data
}

// Bytes returns the private key as bytes
func (priv *PrivateKey) Bytes() []byte {
	return priv.data
}

// PublicKeyFromBytes reconstructs a public key from bytes
func PublicKeyFromBytes(data []byte, mode Mode) (*PublicKey, error) {
	var expectedSize int

	switch mode {
	case MLKEM512:
		expectedSize = MLKEM512PublicKeySize
	case MLKEM768:
		expectedSize = MLKEM768PublicKeySize
	case MLKEM1024:
		expectedSize = MLKEM1024PublicKeySize
	default:
		return nil, errors.New("invalid ML-KEM mode")
	}

	if len(data) != expectedSize {
		return nil, errors.New("invalid public key size")
	}

	return &PublicKey{
		mode: mode,
		data: data,
	}, nil
}

// PrivateKeyFromBytes reconstructs a private key from bytes
func PrivateKeyFromBytes(data []byte, mode Mode) (*PrivateKey, error) {
	var expectedPrivSize, expectedPubSize int

	switch mode {
	case MLKEM512:
		expectedPrivSize = MLKEM512PrivateKeySize
		expectedPubSize = MLKEM512PublicKeySize
	case MLKEM768:
		expectedPrivSize = MLKEM768PrivateKeySize
		expectedPubSize = MLKEM768PublicKeySize
	case MLKEM1024:
		expectedPrivSize = MLKEM1024PrivateKeySize
		expectedPubSize = MLKEM1024PublicKeySize
	default:
		return nil, errors.New("invalid ML-KEM mode")
	}

	if len(data) != expectedPrivSize {
		return nil, errors.New("invalid private key size")
	}

	// For placeholder: derive public key from private key deterministically
	// Use first part of private key as seed for public key
	h := sha256.New()
	h.Write(data[:32]) // Use first 32 bytes as seed
	h.Write([]byte("public"))
	pubSeed := h.Sum(nil)

	pubData := make([]byte, expectedPubSize)
	// Fill public key with deterministic data
	for i := 0; i < expectedPubSize; i += 32 {
		h.Reset()
		h.Write(pubSeed)
		h.Write([]byte{byte(i / 32)})
		hash := h.Sum(nil)
		end := i + 32
		if end > expectedPubSize {
			end = expectedPubSize
		}
		copy(pubData[i:end], hash)
	}

	return &PrivateKey{
		PublicKey: PublicKey{
			mode: mode,
			data: pubData,
		},
		data: data,
	}, nil
}