package io.spatio;

import javax.crypto.Cipher;

import javax.crypto.KeyGenerator;

import javax.crypto.SecretKey;

import javax.crypto.spec.GCMParameterSpec;

import javax.crypto.spec.SecretKeySpec;

import java.security.PrivateKey;

import java.security.PublicKey;

import java.security.SecureRandom;

import java.util.Base64;

public final class HybridCrypto {

private static final int GCM_TAG_BITS = 128;

private static final int IV_BYTES = 12;

private HybridCrypto() {}

public static String encrypt(byte[] plaintext, PublicKey publicKey) throws Exception {

// 1) Génère une clé AES

KeyGenerator kg = KeyGenerator.getInstance("AES");

kg.init(256);

SecretKey aesKey = kg.generateKey();

// 2) AES-GCM

byte[] iv = new byte[IV_BYTES];

SecureRandom.getInstanceStrong().nextBytes(iv);

Cipher aes = Cipher.getInstance("AES/GCM/NoPadding");

aes.init(Cipher.ENCRYPT_MODE, aesKey, new GCMParameterSpec(GCM_TAG_BITS, iv));

byte[] ciphertext = aes.doFinal(plaintext);

// 3) Chiffre la clé AES avec RSA-OAEP

Cipher rsa = Cipher.getInstance("RSA/ECB/OAEPWithSHA-256AndMGF1Padding");

rsa.init(Cipher.ENCRYPT_MODE, publicKey);

byte[] encAesKey = rsa.doFinal(aesKey.getEncoded());

// 4) Base64 URL-safe

Base64.Encoder enc = Base64.getUrlEncoder().withoutPadding();

return "v1."

+ enc.encodeToString(encAesKey) + "."

+ enc.encodeToString(iv) + "."

+ enc.encodeToString(ciphertext);

}

public static byte[] decrypt(String payload, PrivateKey privateKey) throws Exception {

String[] parts = payload.split("\\.");

if (parts.length != 4 || !"v1".equals(parts[0])) {

throw new IllegalArgumentException("Payload invalide");

}

Base64.Decoder dec = Base64.getUrlDecoder();

byte[] encAesKey = dec.decode(parts[1]);

byte[] iv = dec.decode(parts[2]);

byte[] ciphertext = dec.decode(parts[3]);

// 1) Déchiffre la clé AES avec la clé privée RSA

Cipher rsa = Cipher.getInstance("RSA/ECB/OAEPWithSHA-256AndMGF1Padding");

rsa.init(Cipher.DECRYPT_MODE, privateKey);

byte[] aesKeyBytes = rsa.doFinal(encAesKey);

SecretKey aesKey = new SecretKeySpec(aesKeyBytes, "AES");

// 2) Déchiffre le message

Cipher aes = Cipher.getInstance("AES/GCM/NoPadding");

aes.init(Cipher.DECRYPT_MODE, aesKey, new GCMParameterSpec(GCM_TAG_BITS, iv));

return aes.doFinal(ciphertext);

}

}