com.demandware.vulnapp.challenge.impl.ECBOracleChallenge.java Source code

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Here is the source code for com.demandware.vulnapp.challenge.impl.ECBOracleChallenge.java

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/*
 * Copyright 2016 Demandware Inc.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *     http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.demandware.vulnapp.challenge.impl;

import java.io.UnsupportedEncodingException;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.util.Arrays;

import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.KeyGenerator;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.SecretKey;

import org.apache.commons.codec.DecoderException;
import org.apache.commons.codec.binary.Hex;

import com.demandware.vulnapp.challenge.AbstractChallenge;
import com.demandware.vulnapp.servlet.DIVAServletRequestWrapper;
import com.demandware.vulnapp.servlet.Dictionary;
import com.demandware.vulnapp.util.exception.SetupRuntimeException;

/**
 * Execute a Chosen-platintext attack to reveal the AES-ECB encrypted string
 * 
 * @author Chris Smith
 *
 */
public class ECBOracleChallenge extends AbstractChallenge {
    public static final String FLAG_PARAM = "encrypted_flag";

    public static final String INPUT_VAL = "input";

    private final String encryptionType;
    private final String keyType;
    private final Cipher eCipher;
    private final Cipher dCipher;

    protected ECBOracleChallenge(String name) {
        super(name);
        this.keyType = "AES";
        this.encryptionType = "AES/ECB/NoPadding";
        try {
            SecretKey key = generateKey();
            this.eCipher = Cipher.getInstance(this.encryptionType);
            this.eCipher.init(Cipher.ENCRYPT_MODE, key);
            this.dCipher = Cipher.getInstance(this.encryptionType);
            this.dCipher.init(Cipher.DECRYPT_MODE, key);
        } catch (NoSuchAlgorithmException | NoSuchPaddingException | InvalidKeyException e) {
            throw new SetupRuntimeException(e);
        }
        tryRoundtrip();
    }

    /**
     * it's easy to mess up the encryption depending on implementation 
     * and some odd changes for certain JVMs. This is a sanity check.
     */
    private void tryRoundtrip() {
        try {
            String test = "foobar";
            String enc = encryptValue(test);
            String dec = decryptValue(enc);
            if (!test.equals(dec)) {
                throw new SetupRuntimeException("ECB roundtrip failed");
            }
        } catch (Exception e) {
            throw new SetupRuntimeException(e);
        }
    }

    /**
     * Generate some key such that we don't know the key value so noone can just
     * use the key
     */
    private SecretKey generateKey() throws NoSuchAlgorithmException {
        KeyGenerator keyGen = KeyGenerator.getInstance(this.keyType);
        return keyGen.generateKey();
    }

    /**
     * entrance to challenge
     */
    public String handleChallengeRequest(DIVAServletRequestWrapper req) {
        String value = null;
        String flag = (String) req.getInformation(Dictionary.FLAG_VALUE);
        String input = req.getParameter(FLAG_PARAM);
        ;
        String toBeEnc = generateStringForEncryption(input, flag);
        if (toBeEnc != null) {
            try {
                value = encryptValue(toBeEnc);
            } catch (Exception e) {
                value = "Error encrypting";
            }
        }
        return value;
    }

    /**
     * combine user input and flag values
     */
    private String generateStringForEncryption(String input, String flag) {
        StringBuilder sb = new StringBuilder();
        sb.append(ECBOracleChallenge.INPUT_VAL);
        sb.append("=");
        sb.append(input);
        sb.append(";Flag=");
        sb.append(flag);
        sb.append(";");
        return sb.toString();
    }

    /**
     * encrypt the given input with this object's cipher
     * 
     * @return base64 encoded string of the encrypted value
     * @throws UnsupportedEncodingException
     * @throws IllegalBlockSizeException
     * @throws BadPaddingException
     */
    private String encryptValue(String input)
            throws UnsupportedEncodingException, IllegalBlockSizeException, BadPaddingException {
        input = input.trim();
        byte[] inputBytes = input.getBytes();
        int paddedSize = inputBytes.length + (16 - (inputBytes.length % 16));
        inputBytes = Arrays.copyOf(inputBytes, paddedSize);
        byte[] enc = this.eCipher.doFinal(inputBytes);
        return Hex.encodeHexString(enc);
    }

    /**
     * test method, user will never decrypt
     * @throws DecoderException 
     */
    private String decryptValue(String str)
            throws IllegalBlockSizeException, BadPaddingException, UnsupportedEncodingException, DecoderException {
        byte[] dec = Hex.decodeHex(str.toCharArray());
        byte[] decBytes = this.dCipher.doFinal(dec);
        return new String(decBytes).trim();
    }

}