密钥 (SecretKeySpec) 是加密密钥，而不是用户提供的简单明文密码。 AES 标准指定以下密钥大小：128、192 或 256 位。
可以使用密钥派生函数从文本密码创建密钥，例如PBKDF2。
正如评论中提到的Maarten-reinstateMonica，Cipher.getInstance("AES") 会在 ECB 模式下进行 AES 加密，即insecure。 AES-GCM 是基于 AES 算法的强烈认可的 authenticated encryption 模式。
此外，在继续示例代码之前，您需要了解以下概念：
示例代码：
// The number of times that the password is hashed during the derivation of the symmetric key
private static final int PBKDF2_ITERATION_COUNT = 300_000;
private static final int PBKDF2_SALT_LENGTH = 16; //128 bits
private static final int AES_KEY_LENGTH = 256; //in bits
// An initialization vector size
private static final int GCM_NONCE_LENGTH = 12; //96 bits
// An authentication tag size
private static final int GCM_TAG_LENGTH = 128; //in bits
private static byte[] encryptAES256(byte[] input, String password) {
try {
SecureRandom secureRandom = SecureRandom.getInstanceStrong();
// Derive the key, given password and salt
SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA512");
// A salt is a unique, randomly generated string
// that is added to each password as part of the hashing process
byte[] salt = new byte[PBKDF2_SALT_LENGTH];
secureRandom.nextBytes(salt);
KeySpec keySpec =
new PBEKeySpec(password.toCharArray(), salt, PBKDF2_ITERATION_COUNT, AES_KEY_LENGTH);
byte[] secret = factory.generateSecret(keySpec).getEncoded();
SecretKey key = new SecretKeySpec(secret, "AES");
// AES-GCM encryption
Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
// A nonce or an initialization vector is a random value chosen at encryption time
// and meant to be used only once
byte[] nonce = new byte[GCM_NONCE_LENGTH];
secureRandom.nextBytes(nonce);
// An authentication tag
GCMParameterSpec gcmParameterSpec = new GCMParameterSpec(GCM_TAG_LENGTH, nonce);
cipher.init(Cipher.ENCRYPT_MODE, key, gcmParameterSpec);
byte[] encrypted = cipher.doFinal(input);
// Salt and nonce can be stored together with the encrypted data
// Both salt and nonce have fixed length, so can be prefixed to the encrypted data
ByteBuffer byteBuffer = ByteBuffer.allocate(salt.length + nonce.length + encrypted.length);
byteBuffer.put(salt);
byteBuffer.put(nonce);
byteBuffer.put(encrypted);
return byteBuffer.array();
} catch (Exception e) {
throw new RuntimeException(e);
}
}
private static byte[] decryptAES256(byte[] encrypted, String password) {
try {
// Salt and nonce have to be extracted
ByteBuffer byteBuffer = ByteBuffer.wrap(encrypted);
byte[] salt = new byte[PBKDF2_SALT_LENGTH];
byteBuffer.get(salt);
byte[] nonce = new byte[GCM_NONCE_LENGTH];
byteBuffer.get(nonce);
byte[] cipherBytes = new byte[byteBuffer.remaining()];
byteBuffer.get(cipherBytes);
SecretKeyFactory factory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA512");
KeySpec keySpec =
new PBEKeySpec(password.toCharArray(), salt, PBKDF2_ITERATION_COUNT, AES_KEY_LENGTH);
byte[] secret = factory.generateSecret(keySpec).getEncoded();
SecretKey key = new SecretKeySpec(secret, "AES");
Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
// If encrypted data is altered, during decryption authentication tag verification will fail
// resulting in AEADBadTagException
GCMParameterSpec gcmParameterSpec = new GCMParameterSpec(GCM_TAG_LENGTH, nonce);
cipher.init(Cipher.DECRYPT_MODE, key, gcmParameterSpec);
return cipher.doFinal(cipherBytes);
} catch (Exception e) {
throw new RuntimeException(e);
}
}
public static void main(String[] args) throws Exception {
String password = "Q8yRrM^AvV5r8Yx+"; //Password still has to be strong ehough
String input = "Sample text to encrypt";
byte[] encrypted = encryptAES256(input.getBytes(UTF_8), password);
System.out.println(Base64.getEncoder().encodeToString(encrypted));
//s+AwwowLdSb3rFZ6jJlxSXBvzGz7uB6+g2e97QXGRKUY5sHPgf94AOoybkzuR3rNREMj56Ik1+Co682s4vT2sAQ/
byte[] decrypted = decryptAES256(encrypted, password);
System.out.println(new String(decrypted, UTF_8));
//Sample text to encrypt
}
关于random nonces 的更多内容。如果只有少数记录使用相同的密钥加密，那么随机 nonce 不会造成风险。但是，如果使用相同的密钥对大量记录进行加密，则风险可能会变得相关。
一个重复的随机数通常足以完全恢复
连接的身份验证密钥。在这种错误的实现中，
真实性丢失，攻击者能够操纵
受 TLS 保护的内容。
出于安全原因，应避免随机数，并应使用计数器。