Automatic login through banner¶

import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.io.ByteArrayOutputStream;
import java.nio.charset.StandardCharsets;
import java.util.Arrays;
import java.util.Base64;
import java.util.zip.Inflater;

public class Main {

    public static void main(String[] args) throws Exception {
        String sampleEncryptedData = "pn126XOrtRWEt8maRZtapHzAIHNWSdD45abmOkHQ4-wx4PqPRYjYNnhzHe_Mv5gqpXeNcrFgkvihRGo6fSN2ZSWyVGrocK2LxfYHtPJ8XRU5SZ_LDG0Mvquebusurpix0_iiOHn5bmMaxlSDeEVHTM5CoRQpPMDY8j9D44QJL9tw5R_2h-utzs244r0OcAJRkFyHggZDRnhC5rqUQgyRu1mEYVhXvmiX0wIjEpnPapkbmngEm2f-IPWIsdhunBXoCyf1OcpVutpGZ4ARZRbuhQ";
        String sampleEncryptionKey = "5725f257285ac6a56e6ec94b0cac84d565e8d7dc8ea4828446b04e8d2d3f0e2d";
        String json = decodeSecure(sampleEncryptedData, sampleEncryptionKey);
        System.out.println(json);
    }

    public static String decodeSecure(String encoded, String hexKey) throws Exception {
        byte[] key = hexToBytes(hexKey);
        byte[] decoded = safeBase64Decode(encoded);
        int ivLength = 16; // AES block size
        byte[] iv = Arrays.copyOfRange(decoded, 0, ivLength);
        byte[] encrypted = Arrays.copyOfRange(decoded, ivLength, decoded.length);

        byte[] decryptedNoPad = aes256CbcNoPadding(encrypted, key, iv);
        byte[] unpadded = zeroUnpad(decryptedNoPad);
        byte[] inflated = zlibInflate(unpadded);
        return new String(inflated, StandardCharsets.UTF_8);
    }

    private static byte[] hexToBytes(String hex) {
        int len = hex.length();
        byte[] data = new byte[len / 2];
        for (int i = 0; i < len; i += 2) {
            data[i / 2] = (byte) ((Character.digit(hex.charAt(i), 16) << 4)
                    + Character.digit(hex.charAt(i + 1), 16));
        }
        return data;
    }

    private static byte[] safeBase64Decode(String input) {
        String base64 = input.replace('-', '+').replace('_', '/');
        int mod = base64.length() % 4;
        if (mod != 0) base64 += "====".substring(mod);
        return Base64.getDecoder().decode(base64);
    }

    private static byte[] aes256CbcNoPadding(byte[] ciphertext, byte[] key, byte[] iv) throws Exception {
        Cipher cipher = Cipher.getInstance("AES/CBC/NoPadding");
        SecretKeySpec keySpec = new SecretKeySpec(key, "AES");
        IvParameterSpec ivSpec = new IvParameterSpec(iv);
        cipher.init(Cipher.DECRYPT_MODE, keySpec, ivSpec);
        return cipher.doFinal(ciphertext);
    }

    private static byte[] zeroUnpad(byte[] data) {
        int i = data.length - 1;
        while (i >= 0 && data[i] == 0) i--;
        return Arrays.copyOfRange(data, 0, i + 1);
    }

    // Uses zlib (RFC1950) format. Set nowrap=false in Inflater.
    private static byte[] zlibInflate(byte[] data) throws Exception {
        Inflater inflater = new Inflater(false);
        inflater.setInput(data);
        byte[] buffer = new byte[4096];
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        try {
            while (!inflater.finished()) {
                int count = inflater.inflate(buffer);
                if (count == 0 && inflater.needsInput()) break;
                if (count > 0) baos.write(buffer, 0, count);
            }
        } finally {
            inflater.end();
        }
        return baos.toByteArray();
    }
}