Reference Core Java Volume Ⅱ 10th Edition
1 对称加密
“Java密码扩展”包含了一个Cipher
,它是所有密码算法的超类。通过getInstance(algorithmName)
可以获得一个密码对象。
cipher.init(mode, key);模式有以下四种:
Cipher.ENCRYPT;
Cipher.DECRYPT;
Cipher.WRAP_MODE和Cipher.UNWRAP_MODE会用一个秘钥对另一个秘钥进行加密
// 可以一直调用cipher.update(),进行加密int blockSize = cipher.getBlockSize();byte[] inBytes = new byte[blockSize];... // read inBytesint outputSize = cipher.getOutputSize(blockSize);byte[] outBytes = new byte[outputSize];int outLength = cipher.update(inBytes, 0, outputSize, outBytes);... // write outBytes//完成上述操作后,最后必须调用doFinal返回加密后的数据//如果最后一个输入数据块小于blockSize:outBytes = cipher.doFinal(inBytes, 0, inLength);//如果所有数据都已加密:outBytes = cipher.doFinal();//如果输入数组长度不够blockSize,update方法返回的数组为空,长度为0
doFinal调用时必要的,因为它会对最后的数据块进行填充,常用填充方案是RSA Security公司在公共秘钥密码标准#5(Public Key Cryptography Standard, PKCS)中描述的方案
该方案最后一个数据块不是全用0填充,而是等于填充字节数量的值最为填充值
2 秘钥生成
我们需要确保秘钥生成时随机的。这需要遵循下面的步骤:
1). 为加密算法获取KeyGenerator
2). 用随机源来初始化秘钥发生器。如果密码长度是可变的,还需要指定期望的密码块长度
3). 调用generateKey方法
例如:
KeyGenerator keygen = KeyGenerator.getInstance("AES");SecureRandom random = new SecureRandom();keygen.init(random);SecretKey key = keygen.generateKey();
或者可以从一组固定的原生数据(也许是口令或者随机键产生的)中生成一个密钥,这时可以使用SecretKeyFactory
byte[] keyData = …; // 16 byte for AES
SecretKey key = new SecretKeySpec(keyData, “AES”);
如果要生成密钥,必须使用“真正的随机”数。例如,在常见的Random中的常规的随即发生器。是根据当前的日期和时间来产生的,因此它不够随机。假设计算机时钟可以精确到1/10秒,那么每天最多存在864000个种子。如果攻击者知道密钥的日期(通常可以由消息日期或证书有效日期推算出来),那么就可以很容易的产生那一天的所有可能的种子。
SecureRandom类产生的随机数,远比由Random类产生的那些随机数字安全得多。也可以由我们提供种子。由setSeed(byre[] b)方法传递给它。
如果没有随机数发生器提供种子,那么它将通过启动线程,是他们睡眠,然后测量他们被唤醒的准确时间,一次来计算自己的20个字节的种子
!注意: 这个算法仍然被人为是安全的。而且,在过去,依靠对诸如硬盘访问之间的类的其他计算机组件进行计时的算法, 后来也被证明不也是完全随机的。
3 密码流
密码流能够透明地调用update和doFinal方法,所以非常方便,源码也很简单。
API javax.crypto.CipherInputStream 1.4
CipherInputStream(InputStream in, Cipher cipher)
构建一个输入流,读取in中的数据,并且使用指定的密码对数据进行解密和加密。int read()
int read(byte[] b, int off, int len)
读取输入流中的数据,该数据会被自动解密和加密
API javax.crypto.CipherOutputStream 1.4
CipherOutputSream(OutputStream out, Cipher cipher)
构建一个输出流,以便将数据写入out,并且使用指定的秘密对数据进行加密和解密。void write(int ch)
void write(byte b, int off, int len)
将数据写入输出流,该数据会被自动加密和解密。void flush()
刷新密码缓冲区,如果需要的化,执行填充操作。
CipherInputStream.read读取完数据后,如果不够一个数据块,会自动调用doFinal方法填充后返回
CipherOutputStream.close方法如果发现,还有没写完的数据,会调用doFinal方法返回数据然后输出
4 工具类
import javax.crypto.*;import javax.crypto.spec.IvParameterSpec;import javax.crypto.spec.SecretKeySpec;import java.io.*;import java.nio.charset.Charset;import java.nio.charset.StandardCharsets;import java.nio.file.Files;import java.security.*;import java.security.spec.AlgorithmParameterSpec;import java.util.Base64;import java.util.Objects;/** * 加解密字符串、文件工具类 * @author YYang 13047 * @version 2022/10/25 12:10 */public class AESUtils { public static final String AES = "AES"; //PKCS: Public Key Cryptographic Standard public static final String AES_ECB = "AES/ECB/PKCS5Padding"; public static final String AES_CBC = "AES/CBC/PKCS5Padding"; public static final String AES_CFB = "AES/CFB/PKCS5Padding"; public static final int KEY_SIZE = 128; public static final int BUFFER_SIZE = 512; public static String encodeToString(byte[] unEncoded) { return Base64.getEncoder().encodeToString(unEncoded); } public static byte[] decode(String encoded) { return Base64.getDecoder().decode(encoded); } public static String generateAESKey() throws NoSuchAlgorithmException { return generateAESKey(KEY_SIZE, null); } /** * @param keySize keySize must be equal to 128, 192 or 256; * @param seed 随机数种子 * @see #generateAESKey0() */ public static String generateAESKey(int keySize, String seed) throws NoSuchAlgorithmException { KeyGenerator keyGen = KeyGenerator.getInstance(AES); SecureRandom random = (seed == null || seed.length() == 0) ? new SecureRandom() : new SecureRandom(seed.getBytes(StandardCharsets.UTF_8)); //如果不初始化,SunJCE默认使用new SecureRandom() keyGen.init(keySize, random); SecretKey secretKey = keyGen.generateKey(); return encodeToString(secretKey.getEncoded()); } /** * @return 密钥,不初始化,使用默认的 */ public static String generateAESKey0() throws NoSuchAlgorithmException { return encodeToString(KeyGenerator.getInstance(AES).generateKey().getEncoded()); } /** * @param algorithm 算法名 * @return 返回一个当前算法BlockSize大小的随机数组,然后Base64转码 * @see #generateAESIv() */ public static String generateAESIv(String algorithm) throws NoSuchAlgorithmException, NoSuchPaddingException { Cipher cipher = Cipher.getInstance(algorithm); int blockSize = cipher.getBlockSize(); byte[] ivByte = new byte[blockSize]; new SecureRandom().nextBytes(ivByte); return encodeToString(ivByte); } public static String generateAESIv() { //AES blockSize == 16 byte[] bytes = new byte[16]; new SecureRandom().nextBytes(bytes); return encodeToString(bytes); } public static AlgorithmParameterSpec getIv(String ivStr) { if (ivStr == null || ivStr.length() < 1) return null; return new IvParameterSpec(decode(ivStr)); } /** * @return 指定秘钥和算法,返回Key对象 */ public static Key getKey(String keyStr, String algorithm) { return new SecretKeySpec(decode(keyStr), algorithm); } public static Cipher initCipher(String algorithm, int cipherMode, Key key, AlgorithmParameterSpec param) throws NoSuchPaddingException, NoSuchAlgorithmException, InvalidKeyException, InvalidAlgorithmParameterException { Cipher cipher = Cipher.getInstance(algorithm); if (param == null) { cipher.init(cipherMode, key); } else { cipher.init(cipherMode, key, param); } return cipher; } public static String encrypt(String algorithm, String keyStr, String ivStr, String unencryptedStr) throws Exception { return encrypt(algorithm, keyStr, ivStr, unencryptedStr, StandardCharsets.UTF_8); } public static String encrypt(String algorithm, String keyStr, String ivStr, String unencryptedStr, Charset charset) throws Exception { Cipher cipher = initCipher(algorithm, Cipher.ENCRYPT_MODE, getKey(keyStr, AES), getIv(ivStr)); byte[] encrypted = cipher.doFinal(unencryptedStr.getBytes(charset)); return encodeToString(encrypted); } public static String decrypt(String algorithm, String keyStr, String ivStr, String encryptedStr) throws Exception { return decrypt(algorithm, keyStr, ivStr, encryptedStr, StandardCharsets.UTF_8); } public static String decrypt(String algorithm, String keyStr, String ivStr, String encryptedStr, Charset charset) throws Exception { Cipher cipher = initCipher(algorithm, Cipher.DECRYPT_MODE, getKey(keyStr, AES), getIv(ivStr)); byte[] decrypted = cipher.doFinal(decode(encryptedStr)); return new String(decrypted, charset); } /** * 解密文件 */ public static void encryptFile(String algorithm, String keyStr, String ivStr, File source, File target) throws Exception { checkPath(source, target); Cipher cipher = initCipher(algorithm, Cipher.ENCRYPT_MODE, getKey(keyStr, AES), getIv(ivStr)); try (FileOutputStream fos = new FileOutputStream(target); CipherInputStream cis = new CipherInputStream(new FileInputStream(source), cipher)) { byte[] buffer = new byte[BUFFER_SIZE]; int len; while ((len = cis.read(buffer)) != -1) { fos.write(buffer, 0, len); } fos.flush(); } } /** * 加密文件 */ public static void decryptFile(String algorithm, String keyStr, String ivStr, File source, File target) throws Exception { checkPath(source, target); Cipher cipher = initCipher(algorithm, Cipher.DECRYPT_MODE, getKey(keyStr, AES), getIv(ivStr)); try (FileInputStream fis = new FileInputStream(source); CipherOutputStream cos = new CipherOutputStream(new FileOutputStream(target), cipher)) { byte[] buffer = new byte[BUFFER_SIZE]; int len; while ((len = fis.read(buffer)) != -1) { cos.write(buffer, 0, len); } cos.flush(); } } public static void checkPath(File source, File target) throws IOException { Objects.requireNonNull(source); Objects.requireNonNull(target); if (source.isDirectory() || !source.exists()) { throw new FileNotFoundException(source.toString()); } if (Objects.equals(source.getCanonicalPath(), target.getCanonicalPath())) { throw new IllegalArgumentException("sourceFile equals targetFile"); } File parentDirectory = target.getParentFile(); if (parentDirectory != null && !parentDirectory.exists()) { Files.createDirectories(parentDirectory.toPath()); } } public static void main(String[] args) throws Exception { System.out.println(generateAESKey()); System.out.println(generateAESIv(AES_ECB)); String keyStr = "dN2VIV86Z2ShT47pEC1XwQ=="; String ivStr = "00hDTDhCxa9t11TrQSso3w=="; String encrypted = encrypt(AES_CBC, keyStr, ivStr, "中国深圳"); System.out.println("encrypted:" + encrypted); System.out.println(decrypt(AES_CBC, keyStr, ivStr, encrypted)); File source = new File("README.md"); File encryptedFile = new File("out/README1.md"); File decryptedFile = new File("out/README2.md"); encryptFile(AES_CBC, keyStr, ivStr, source, encryptedFile); decryptFile(AES_CBC, keyStr, ivStr, encryptedFile, decryptedFile); }}