feat: Add encryption service with AES-GCM, field-level encryption, and PBKDF2 key derivation

- Add EncryptionService struct with masterKey and gcm cipher fields
- Add EncryptionConfig with MasterKey and KeyDerivationSalt fields
- Add NewEncryptionService constructor with PBKDF2 key derivation, 100000 iterations, and AES-GCM cipher initialization
- Add Encrypt and Decrypt methods with nonce generation and validation
- Add EncryptString and DecryptString methods with base64 encoding
- Add FieldEncryptor struct

apps/carrier-connector/internal/security/encryption.go

@@ -0,0 +1,152 @@
+package security
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/rand"
+	"crypto/sha256"
+	"encoding/base64"
+	"errors"
+	"io"
+
+	"golang.org/x/crypto/pbkdf2"
+)
+
+// EncryptionService provides data encryption at rest
+type EncryptionService struct {
+	masterKey []byte
+	gcm       cipher.AEAD
+}
+
+// EncryptionConfig configures encryption
+type EncryptionConfig struct {
+	MasterKey string
+	KeyDerivationSalt string
+}
+
+// NewEncryptionService creates a new encryption service
+func NewEncryptionService(config EncryptionConfig) (*EncryptionService, error) {
+	salt := []byte(config.KeyDerivationSalt)
+	if len(salt) == 0 {
+		salt = []byte("telecom-platform-default-salt")
+	}
+
+	key := pbkdf2.Key([]byte(config.MasterKey), salt, 100000, 32, sha256.New)
+
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return nil, err
+	}
+
+	gcm, err := cipher.NewGCM(block)
+	if err != nil {
+		return nil, err
+	}
+
+	return &EncryptionService{
+		masterKey: key,
+		gcm:       gcm,
+	}, nil
+}
+
+// Encrypt encrypts plaintext data
+func (e *EncryptionService) Encrypt(plaintext []byte) ([]byte, error) {
+	nonce := make([]byte, e.gcm.NonceSize())
+	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
+		return nil, err
+	}
+
+	ciphertext := e.gcm.Seal(nonce, nonce, plaintext, nil)
+	return ciphertext, nil
+}
+
+// Decrypt decrypts ciphertext data
+func (e *EncryptionService) Decrypt(ciphertext []byte) ([]byte, error) {
+	if len(ciphertext) < e.gcm.NonceSize() {
+		return nil, errors.New("ciphertext too short")
+	}
+
+	nonce := ciphertext[:e.gcm.NonceSize()]
+	ciphertext = ciphertext[e.gcm.NonceSize():]
+
+	plaintext, err := e.gcm.Open(nil, nonce, ciphertext, nil)
+	if err != nil {
+		return nil, err
+	}
+
+	return plaintext, nil
+}
+
+// EncryptString encrypts a string and returns base64
+func (e *EncryptionService) EncryptString(plaintext string) (string, error) {
+	encrypted, err := e.Encrypt([]byte(plaintext))
+	if err != nil {
+		return "", err
+	}
+	return base64.StdEncoding.EncodeToString(encrypted), nil
+}
+
+// DecryptString decrypts a base64 string
+func (e *EncryptionService) DecryptString(ciphertext string) (string, error) {
+	data, err := base64.StdEncoding.DecodeString(ciphertext)
+	if err != nil {
+		return "", err
+	}
+	decrypted, err := e.Decrypt(data)
+	if err != nil {
+		return "", err
+	}
+	return string(decrypted), nil
+}
+
+// FieldEncryptor provides field-level encryption for sensitive data
+type FieldEncryptor struct {
+	service *EncryptionService
+	fields  map[string]bool
+}
+
+// NewFieldEncryptor creates a field encryptor
+func NewFieldEncryptor(service *EncryptionService, sensitiveFields []string) *FieldEncryptor {
+	fields := make(map[string]bool)
+	for _, f := range sensitiveFields {
+		fields[f] = true
+	}
+	return &FieldEncryptor{
+		service: service,
+		fields:  fields,
+	}
+}
+
+// IsSensitive checks if a field is sensitive
+func (fe *FieldEncryptor) IsSensitive(field string) bool {
+	return fe.fields[field]
+}
+
+// EncryptField encrypts a field value if sensitive
+func (fe *FieldEncryptor) EncryptField(field, value string) (string, error) {
+	if !fe.IsSensitive(field) {
+		return value, nil
+	}
+	return fe.service.EncryptString(value)
+}
+
+// DecryptField decrypts a field value if sensitive
+func (fe *FieldEncryptor) DecryptField(field, value string) (string, error) {
+	if !fe.IsSensitive(field) {
+		return value, nil
+	}
+	return fe.service.DecryptString(value)
+}
+
+// DefaultSensitiveFields returns commonly sensitive fields
+func DefaultSensitiveFields() []string {
+	return []string{
+		"ssn", "social_security_number",
+		"credit_card", "card_number", "cvv",
+		"password", "secret", "api_key",
+		"phone", "email", "address",
+		"date_of_birth", "dob",
+		"bank_account", "routing_number",
+		"iccid", "imsi", "msisdn",
+	}
+}