[Swift] 64 メモアプリ製作 その16 データ暗号化実装 CryptoKit, キーチェーン

import CryptoKit
import Security
import Foundation

class CryptoManager {
    static let shared = CryptoManager()
    private let key: SymmetricKey
    
    private init() {
        if let keyData = KeychainManager.load(key: "myEncryptionKey") {
            // Keychainからキーを読み込む
            key = SymmetricKey(data: keyData)
        } else {
            // 新しいキーを生成してKeychainに保存する
            let newKey = SymmetricKey(size: .bits256)
            let newKeyData = newKey.withUnsafeBytes { Data($0) }
            let status = KeychainManager.save(key: "myEncryptionKey", data: newKeyData)
            if status == noErr {
                print("新しいキーをKeychainに保存しました。")
                key = newKey
            } else {
                fatalError("キーの保存に失敗しました。")
            }
        }
    }
    
    func encrypt(_ text: String) -> String? {
        guard let data = text.data(using: .utf8) else { return nil }
        do {
            let sealedBox = try AES.GCM.seal(data, using: key)
            return sealedBox.combined?.base64EncodedString()
        } catch {
            print("Encryption error: \(error)")
            return nil
        }
    }

    func decrypt(_ encryptedText: String) -> String? {
        guard let data = Data(base64Encoded: encryptedText),
              let sealedBox = try? AES.GCM.SealedBox(combined: data) else { return nil }
        do {
            let decryptedData = try AES.GCM.open(sealedBox, using: key)
            return String(data: decryptedData, encoding: .utf8)
        } catch {
            print("Decryption error: \(error)")
            return nil
        }
    }

}

class KeychainManager {
    static func save(key: String, data: Data) -> OSStatus {
        let query = [
            kSecClass as String       : kSecClassGenericPassword as String,
            kSecAttrAccount as String : key,
            kSecValueData as String   : data ] as [String : Any]

        SecItemDelete(query as CFDictionary) // 既存のアイテムを削除
        return SecItemAdd(query as CFDictionary, nil)
    }
    
    static func load(key: String) -> Data? {
        let query = [
            kSecClass as String       : kSecClassGenericPassword,
            kSecAttrAccount as String : key,
            kSecReturnData as String  : kCFBooleanTrue!,
            kSecMatchLimit as String  : kSecMatchLimitOne ] as [String : Any]

        var item: CFTypeRef?
        let status = SecItemCopyMatching(query as CFDictionary, &item)
        if status == noErr {
            return item as? Data
        }
        return nil
    }
}