Javaでのストレッチングとは？安全なパスワード管理のための基本技術

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;

public class StretchingExample {
    public static void main(String[] args) {
        String password = "mySecret123";
        String salt = "randomSalt";
        int iterations = 10000;

        try {
            MessageDigest md = MessageDigest.getInstance("SHA-256");

            byte[] input = (salt + password).getBytes();

            for (int i = 0; i < iterations; i++) {
                input = md.digest(input);
            }

            // ハッシュ値を16進数に変換
            StringBuilder sb = new StringBuilder();
            for (byte b : input) {
                sb.append(String.format("%02x", b));
            }

            System.out.println("ストレッチング後のハッシュ値: " + sb.toString());

        } catch (NoSuchAlgorithmException e) {
            e.printStackTrace();
        }
    }
}

import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.PBEKeySpec;
import java.security.SecureRandom;
import java.util.Base64;

public class PBKDF2Example {
    public static void main(String[] args) throws Exception {
        String password = "mySecret123";
        byte[] salt = new byte[16];
        SecureRandom sr = new SecureRandom();
        sr.nextBytes(salt);

        PBEKeySpec spec = new PBEKeySpec(password.toCharArray(), salt, 65536, 256); // 65536回、256bit
        SecretKeyFactory skf = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA256");
        byte[] hash = skf.generateSecret(spec).getEncoded();

        System.out.println("Salt: " + Base64.getEncoder().encodeToString(salt));
        System.out.println("Hash: " + Base64.getEncoder().encodeToString(hash));
    }
}