com.predic8.membrane.core.interceptor.security.PaddingHeaderInterceptor Maven / Gradle / Ivy

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/* Copyright 2023 predic8 GmbH, www.predic8.com

   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.predic8.membrane.core.interceptor.security;

import com.predic8.membrane.annot.MCAttribute;
import com.predic8.membrane.annot.MCElement;
import com.predic8.membrane.core.exchange.Exchange;
import com.predic8.membrane.core.http.*;
import com.predic8.membrane.core.interceptor.AbstractInterceptor;
import com.predic8.membrane.core.interceptor.Outcome;

import java.security.SecureRandom;

import static com.predic8.membrane.core.interceptor.Interceptor.Flow.REQUEST;
import static com.predic8.membrane.core.interceptor.Interceptor.Flow.RESPONSE;
import static com.predic8.membrane.core.interceptor.Outcome.CONTINUE;
import static java.util.EnumSet.of;


// TODO JAVADOC!
/**
 * Uses secure random function for the random length according to FIPS 140-2 standard.
 */
@MCElement(name = "paddingHeader")
public class PaddingHeaderInterceptor extends AbstractInterceptor {
    static final String LOOKUP_TABLE = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789 _:;.,\\/\"'?!(){}[]@<>=-+*#$&`|~^%";
    static final String X_PADDING = "X-Padding";
    private int roundUp = 20;
    private int constant = 5;
    private int random = 10;
    private final SecureRandom secRdm = new SecureRandom();

    private void setInterceptorMeta() {
        name = "Padding Header";
        setFlow(of(REQUEST, RESPONSE));
    }

    @SuppressWarnings("unused")
    public PaddingHeaderInterceptor() {
        setInterceptorMeta();
    }

    public PaddingHeaderInterceptor(Integer roundUp, Integer constant, Integer random) {
        setInterceptorMeta();
        this.roundUp = roundUp;
        this.constant = constant;
        this.random = random;
    }

    @Override
    public Outcome handleRequest(Exchange exc) throws Exception {
        return handleInternal(exc.getRequest());
    }

    @Override
    public Outcome handleResponse(Exchange exc) throws Exception {
        return handleInternal(exc.getResponse());
    }

    private Outcome handleInternal(Message msg) {
        msg.getHeader().add(X_PADDING, headerSafePadding(calculatePaddingSize(msg)));
        return CONTINUE;
    }

    public int calculatePaddingSize(Message msg) {
       return calculatePaddingSize(msg.estimateHeapSize());
    }

    public int calculatePaddingSize(long size) {
        return roundUp(size) + constant + getRandomNumber();
    }

    public int getRandomNumber() {
        return secRdm.nextInt(0, random);
    }

    public int roundUp(long n) {
        return (int)(roundUp - (n % roundUp));
    }

    public String headerSafePadding(int len) {
        StringBuilder result = new StringBuilder();

        for (int i = 0; i < len; i++) {
            result.append(getRandomChar());
        }

        return result.toString();
    }

    private char getRandomChar() {
        return LOOKUP_TABLE.charAt(secRdm.nextInt(LOOKUP_TABLE.length()));
    }

    @MCAttribute
    public void setRoundUp(int roundUp) {
        this.roundUp = roundUp;
    }
    @SuppressWarnings("unused")
    public Integer getRoundUp() {
        return roundUp;
    }

    @MCAttribute
    public void setConstant(int constant) {
        this.constant = constant;
    }
    @SuppressWarnings("unused")
    public Integer getConstant() {
        return constant;
    }

    @MCAttribute
    public void setRandom(int random) {
        this.random = random;
    }
    public Integer getRandom() {
        return random;
    }

}