Add encryption/decryption logic

pkg/crypto/encryption/encryption.go

@@ -0,0 +1,296 @@
+/*
+Copyright 2023 The Radius Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package encryption
+
+import (
+	"crypto/cipher"
+	"crypto/rand"
+	"crypto/sha256"
+	"encoding/base64"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+
+	"golang.org/x/crypto/chacha20poly1305"
+)
+
+const (
+	// KeySize is the required size for ChaCha20-Poly1305 keys (256 bits).
+	KeySize = chacha20poly1305.KeySize
+
+	// NonceSize is the size of the nonce for ChaCha20-Poly1305.
+	NonceSize = chacha20poly1305.NonceSize
+)
+
+var (
+	// ErrInvalidKeySize is returned when the encryption key is not the correct size.
+	ErrInvalidKeySize = errors.New("encryption key must be 32 bytes (256 bits)")
+
+	// ErrEncryptionFailed is returned when encryption fails.
+	ErrEncryptionFailed = errors.New("encryption failed")
+
+	// ErrDecryptionFailed is returned when decryption fails.
+	ErrDecryptionFailed = errors.New("decryption failed")
+
+	// ErrInvalidEncryptedData is returned when the encrypted data format is invalid.
+	ErrInvalidEncryptedData = errors.New("invalid encrypted data format")
+
+	// ErrEmptyPlaintext is returned when attempting to encrypt empty data.
+	ErrEmptyPlaintext = errors.New("plaintext cannot be empty")
+
+	// ErrAssociatedDataMismatch is returned when the associated data provided during
+	// decryption does not match what was used during encryption.
+	ErrAssociatedDataMismatch = errors.New("associated data mismatch")
+)
+
+// EncryptedData represents the structure for storing encrypted data.
+// It contains the base64-encoded ciphertext and nonce, plus optional associated data hash.
+type EncryptedData struct {
+	// Version is the key version used for encryption.
+	// This allows decryption to use the correct key when multiple versions exist.
+	Version int `json:"version,omitempty"`
+	// Encrypted contains the base64-encoded ciphertext.
+	Encrypted string `json:"encrypted"`
+	// Nonce contains the base64-encoded nonce used for encryption.
+	Nonce string `json:"nonce"`
+	// AD contains a hash of the associated data used during encryption (optional).
+	// This is stored for verification purposes - the actual AD must be provided during decryption.
+	// The hash allows detection of AD mismatches without exposing the AD value.
+	AD string `json:"ad,omitempty"`
+}
+
+// Encryptor provides methods for encrypting and decrypting data using ChaCha20-Poly1305.
+type Encryptor struct {
+	aead       cipher.AEAD
+	keyVersion int
+}
+
+// NewEncryptor creates a new Encryptor with the provided 256-bit key.
+// Returns an error if the key is not exactly 32 bytes.
+// The key version defaults to 0 (unversioned). Use NewEncryptorWithVersion for versioned keys.
+func NewEncryptor(key []byte) (*Encryptor, error) {
+	return NewEncryptorWithVersion(key, 0)
+}
+
+// NewEncryptorWithVersion creates a new Encryptor with the provided key and version.
+// The version is stored in encrypted data to enable decryption with the correct key.
+func NewEncryptorWithVersion(key []byte, version int) (*Encryptor, error) {
+	if len(key) != KeySize {
+		return nil, ErrInvalidKeySize
+	}
+
+	aead, err := chacha20poly1305.New(key)
+	if err != nil {
+		return nil, fmt.Errorf("%w: %v", ErrEncryptionFailed, err)
+	}
+
+	return &Encryptor{aead: aead, keyVersion: version}, nil
+}
+
+// Encrypt encrypts the plaintext using ChaCha20-Poly1305 with Associated Data (AD).
+// The AD provides authentication for contextual data (like resource ID or field path) without
+// encrypting it. This binds the ciphertext to its context, preventing an attacker from
+// moving encrypted values between different resources or fields.
+//
+// The AD is authenticated but NOT encrypted - it must be provided again during decryption.
+// A hash of the AD is stored in the encrypted data structure to allow early detection of mismatches.
+//
+// Example AD values:
+//   - Resource ID: "/planes/radius/local/resourceGroups/test/providers/Foo.Bar/myResources/test"
+//   - Field path: "credentials.password"
+//   - Combined: resourceID + ":" + fieldPath
+//
+// Pass nil for associatedData if no context binding is needed (not recommended for sensitive data).
+func (e *Encryptor) Encrypt(plaintext []byte, associatedData []byte) ([]byte, error) {
+	if len(plaintext) == 0 {
+		return nil, ErrEmptyPlaintext
+	}
+
+	// Generate a unique nonce for this encryption operation
+	nonce, err := generateNonce(e.aead.NonceSize())
+	if err != nil {
+		return nil, fmt.Errorf("%w: failed to generate nonce: %v", ErrEncryptionFailed, err)
+	}
+
+	// Encrypt the plaintext with associated data
+	// The AD is authenticated (included in the auth tag) but not encrypted
+	ciphertext := e.aead.Seal(nil, nonce, plaintext, associatedData)
+
+	// Create the encrypted data structure
+	encryptedData := EncryptedData{
+		Version:   e.keyVersion,
+		Encrypted: base64.StdEncoding.EncodeToString(ciphertext),
+		Nonce:     base64.StdEncoding.EncodeToString(nonce),
+	}
+
+	// Store a hash of the AD if provided (for verification during decryption)
+	if len(associatedData) > 0 {
+		encryptedData.AD = hashAD(associatedData)
+	}
+
+	// Marshal to JSON
+	result, err := json.Marshal(encryptedData)
+	if err != nil {
+		return nil, fmt.Errorf("%w: failed to marshal encrypted data: %v", ErrEncryptionFailed, err)
+	}
+
+	return result, nil
+}
+
+// Decrypt decrypts the data that was encrypted using the Encrypt method.
+// The associatedData must match what was provided during encryption; if the AD
+// was used during encryption, it must be provided here for successful decryption.
+// The input should be JSON-encoded EncryptedData.
+func (e *Encryptor) Decrypt(data []byte, associatedData []byte) ([]byte, error) {
+	if len(data) == 0 {
+		return nil, ErrInvalidEncryptedData
+	}
+
+	// Parse the encrypted data structure
+	var encryptedData EncryptedData
+	if err := json.Unmarshal(data, &encryptedData); err != nil {
+		return nil, fmt.Errorf("%w: failed to parse encrypted data: %v", ErrInvalidEncryptedData, err)
+	}
+
+	// Verify AD hash matches if AD was used during encryption
+	if encryptedData.AD != "" {
+		if len(associatedData) == 0 {
+			return nil, fmt.Errorf("%w: encrypted data requires associated data but none provided", ErrAssociatedDataMismatch)
+		}
+		if hashAD(associatedData) != encryptedData.AD {
+			return nil, fmt.Errorf("%w: provided associated data does not match", ErrAssociatedDataMismatch)
+		}
+	}
+
+	// Decode the base64-encoded ciphertext
+	ciphertext, err := base64.StdEncoding.DecodeString(encryptedData.Encrypted)
+	if err != nil {
+		return nil, fmt.Errorf("%w: failed to decode ciphertext: %v", ErrInvalidEncryptedData, err)
+	}
+
+	// Decode the base64-encoded nonce
+	nonce, err := base64.StdEncoding.DecodeString(encryptedData.Nonce)
+	if err != nil {
+		return nil, fmt.Errorf("%w: failed to decode nonce: %v", ErrInvalidEncryptedData, err)
+	}
+
+	// Validate nonce size
+	if len(nonce) != e.aead.NonceSize() {
+		return nil, fmt.Errorf("%w: invalid nonce size", ErrInvalidEncryptedData)
+	}
+
+	// Decrypt the ciphertext with the same associated data
+	plaintext, err := e.aead.Open(nil, nonce, ciphertext, associatedData)
+	if err != nil {
+		return nil, fmt.Errorf("%w: %v", ErrDecryptionFailed, err)
+	}
+
+	return plaintext, nil
+}
+
+// EncryptString encrypts a string with associated data and returns the JSON-encoded encrypted data as a string.
+func (e *Encryptor) EncryptString(plaintext string, associatedData []byte) (string, error) {
+	encrypted, err := e.Encrypt([]byte(plaintext), associatedData)
+	if err != nil {
+		return "", err
+	}
+	return string(encrypted), nil
+}
+
+// DecryptString decrypts the JSON-encoded encrypted data with associated data and returns the original string.
+func (e *Encryptor) DecryptString(data string, associatedData []byte) (string, error) {
+	decrypted, err := e.Decrypt([]byte(data), associatedData)
+	if err != nil {
+		return "", err
+	}
+	return string(decrypted), nil
+}
+
+// hashAD creates a truncated SHA-256 hash of the associated data for storage.
+// This allows verification that the correct AD is provided during decryption
+// without storing the actual AD value.
+func hashAD(ad []byte) string {
+	hash := sha256.Sum256(ad)
+	// Use first 16 bytes (128 bits) - sufficient for verification, saves storage
+	return base64.StdEncoding.EncodeToString(hash[:16])
+}
+
+// generateNonce generates a cryptographically secure random nonce.
+func generateNonce(size int) ([]byte, error) {
+	nonce := make([]byte, size)
+	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
+		return nil, err
+	}
+	return nonce, nil
+}
+
+// IsEncryptedData checks if the given data appears to be in the encrypted data format.
+// It validates that the data is valid JSON with non-empty encrypted and nonce fields,
+// and that both fields contain valid base64-encoded data with appropriate nonce size.
+func IsEncryptedData(data []byte) bool {
+	var encryptedData EncryptedData
+	if err := json.Unmarshal(data, &encryptedData); err != nil {
+		return false
+	}
+
+	if encryptedData.Encrypted == "" || encryptedData.Nonce == "" {
+		return false
+	}
+
+	// Validate base64 encoding of ciphertext
+	if _, err := base64.StdEncoding.DecodeString(encryptedData.Encrypted); err != nil {
+		return false
+	}
+
+	// Validate base64 encoding and size of nonce
+	nonce, err := base64.StdEncoding.DecodeString(encryptedData.Nonce)
+	if err != nil {
+		return false
+	}
+
+	// ChaCha20-Poly1305 nonce must be 12 bytes
+	if len(nonce) != NonceSize {
+		return false
+	}
+
+	return true
+}
+
+// GenerateKey generates a new random 256-bit encryption key.
+func GenerateKey() ([]byte, error) {
+	key := make([]byte, KeySize)
+	if _, err := io.ReadFull(rand.Reader, key); err != nil {
+		return nil, fmt.Errorf("failed to generate encryption key: %w", err)
+	}
+	return key, nil
+}
+
+// GetEncryptedDataVersion extracts the key version from encrypted data without decrypting.
+// Returns 0 if the version is not present (for backwards compatibility with unversioned data).
+func GetEncryptedDataVersion(data []byte) (int, error) {
+	if len(data) == 0 {
+		return 0, ErrInvalidEncryptedData
+	}
+
+	var encryptedData EncryptedData
+	if err := json.Unmarshal(data, &encryptedData); err != nil {
+		return 0, fmt.Errorf("%w: failed to parse encrypted data: %v", ErrInvalidEncryptedData, err)
+	}
+
+	return encryptedData.Version, nil
+}