Расшифровка

decrypt.java

public static DecryptedSessionKey decryptSessionKey(PrivateKey pk, EncryptedSessionKey encryptedSessionKey) throws KomandorException {
    SecretKey key_ = null;
    byte[] iv = null;
    try {
      int sizeLength = 4;
      byte[] bKey = Base64.decode(encryptedSessionKey.getEncryptedKey(), Base64.NO_WRAP);
      
      byte[] bBlobLength = SystemUtils.reverseByteArray(Arrays.copyOfRange(bKey, 0, sizeLength));
      int blobLength = ByteBuffer.wrap(bBlobLength).getInt();
      
      byte[] bSimpleBlob = Arrays.copyOfRange(bKey, sizeLength, sizeLength + blobLength);
      byte[] bBlobHeader = Arrays.copyOfRange(bSimpleBlob, 0, 16);
      byte[] sv = Arrays.copyOfRange(bSimpleBlob, 16, 24);
      byte[] bEncryptedKey = Arrays.copyOfRange(bSimpleBlob, 24, 24 + 32);
      byte[] bMacKey = Arrays.copyOfRange(bSimpleBlob, 56, 56 + 4);
      byte[] bEncryptedParams = Arrays.copyOfRange(bSimpleBlob, 60, blobLength);
      
      // Получаем IV вектор
      int IVStart = sizeLength + blobLength;
      byte[] bIVLength = SystemUtils.reverseByteArray(Arrays.copyOfRange(bKey, IVStart, IVStart + sizeLength));
      int IVLength = ByteBuffer.wrap(bIVLength).getInt();
      iv = Arrays.copyOfRange(bKey, IVStart + sizeLength, IVStart + sizeLength + IVLength);
      
      // Получаем зашифрованный ключ
      final Gost28147_89_EncryptedKey ek = new Gost28147_89_EncryptedKey();
      ek.encryptedKey = new Gost28147_89_Key(bEncryptedKey);
      ek.macKey = new Gost28147_89_MAC(bMacKey);
      final Asn1BerEncodeBuffer ebuf = new Asn1BerEncodeBuffer();
      ek.encode(ebuf);
      final byte[] wrap = ebuf.getMsgCopy();
      
      // Генерируем ключ согласования
      SecretKey responderAgree = generateKeyAgreement(pk, encryptedSessionKey.getCertificate(), sv);
      
      if (responderAgree == null) {
        throw new KomandorException("Key agreement is null");
      }
      
      // Расшифровываем ключ
      Cipher cipher = Cipher.getInstance(CIPHER_ALG + CIPHER_KEY_ALG_PARAMS);
      cipher.init(Cipher.UNWRAP_MODE, responderAgree);
      key_ = (SecretKey) cipher.unwrap(wrap, null, Cipher.SECRET_KEY);
    } catch (Exception e) {
      throw new KomandorException(e);
    }
    return new DecryptedSessionKey(key_, iv);
  }

private static SecretKey generateKeyAgreement(PrivateKey pk, X509Certificate partnerCert, byte[] sv) throws NoSuchProviderException, NoSuchAlgorithmException, InvalidAlgorithmParameterException, InvalidKeyException {
    final IvParameterSpec ivspec = new IvParameterSpec(sv);
    final KeyAgreement keyAgree = KeyAgreement.getInstance(pk.getAlgorithm(), JCSP.PROVIDER_NAME);
    keyAgree.init(pk, ivspec, null);
    keyAgree.doPhase(partnerCert.getPublicKey(), true);
    return keyAgree.generateSecret(CIPHER_ALG);
  }