Kryptografie

package at.aydin.lab.crypto.legacy;

// Design Pattern: Security Gateway (Legacy-Antipattern) – bündelt Kryptografie, verwendet absichtlich unsicheres ECB.
import javax.crypto.*;
import javax.crypto.spec.*;
import java.nio.charset.StandardCharsets;
import java.security.*;
import java.util.*;

/** Lern-Antipattern: AES/ECB ist deterministisch und für produktive Daten ungeeignet. */
public final class LegacyAesEcb {
    private SecretKey key(String password) throws Exception {
        return new SecretKeySpec(Arrays.copyOf(MessageDigest.getInstance("SHA-256").digest(password.getBytes(StandardCharsets.UTF_8)),
            16), "AES");
    }

    public String encrypt(String text, String password) throws Exception {
        Cipher c = Cipher.getInstance("AES/ECB/PKCS5Padding");
        c.init(Cipher.ENCRYPT_MODE, key(password));
        return Base64.getEncoder().encodeToString(c.doFinal(text.getBytes(StandardCharsets.UTF_8)));
    }

    public String decrypt(String value, String password) throws Exception {
        Cipher c = Cipher.getInstance("AES/ECB/PKCS5Padding");
        c.init(Cipher.DECRYPT_MODE, key(password));
        return new String(c.doFinal(Base64.getDecoder().decode(value)), StandardCharsets.UTF_8);
    }
}

package at.aydin.lab.crypto.modern;

import javax.crypto.*;
import javax.crypto.spec.*;
import java.nio.charset.StandardCharsets;
import java.security.*;

// Design Pattern: Security Gateway
// Zweck: Sichere kryptografische Parameter werden zentral erzwungen.
public final class AesGcmService {
    private final SecureRandom random = new SecureRandom();
    private SecretKey key(char[] password, byte[] salt) throws Exception {
        var f = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA256");
        return new SecretKeySpec(f.generateSecret(new PBEKeySpec(password, salt, 120_000, 256)).getEncoded(), "AES");
    }

    public EncryptedPayload encrypt(String text, char[] password) throws Exception {
        byte[] salt = new byte[16], iv = new byte[12];
        random.nextBytes(salt);
        random.nextBytes(iv);
        Cipher c = Cipher.getInstance("AES/GCM/NoPadding");
        c.init(Cipher.ENCRYPT_MODE, key(password, salt), new GCMParameterSpec(128, iv));
        return new EncryptedPayload(salt, iv, c.doFinal(text.getBytes(StandardCharsets.UTF_8)));
    }

    public String decrypt(EncryptedPayload p, char[] password) throws Exception {
        Cipher c = Cipher.getInstance("AES/GCM/NoPadding");
        c.init(Cipher.DECRYPT_MODE, key(password, p.salt()), new GCMParameterSpec(128, p.iv()));
        return new String(c.doFinal(p.cipherText()), StandardCharsets.UTF_8);
    }
}

package at.aydin.lab.crypto.modern;

// Design Pattern: Value Object
// Zweck: Ciphertext, Salt und IV bleiben als untrennbare verschlüsselte Nutzlast zusammen.
public record EncryptedPayload(byte[] salt, byte[] iv, byte[] cipherText) {
    public EncryptedPayload {
        salt = salt.clone();
        iv = iv.clone();
        cipherText = cipherText.clone();
    }

    public byte[] salt() {
        return salt.clone();
    }

    public byte[] iv() {
        return iv.clone();
    }

    public byte[] cipherText() {
        return cipherText.clone();
    }
}