88 lines
3.4 KiB
Java
88 lines
3.4 KiB
Java
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/*
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* Copyright 2021 Paul Schaub.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package org.pgpainless.algorithm.negotiation;
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import java.util.ArrayList;
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import java.util.Collections;
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import java.util.Comparator;
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import java.util.LinkedHashMap;
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import java.util.List;
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import java.util.Map;
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import java.util.Set;
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import org.pgpainless.algorithm.SymmetricKeyAlgorithm;
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import org.pgpainless.policy.Policy;
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/**
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* Interface for symmetric key algorithm negotiation.
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*/
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public interface SymmetricKeyAlgorithmNegotiator {
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/**
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* Negotiate a symmetric encryption algorithm.
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*
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* @param policy algorithm policy
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* @param override algorithm override (if not null, return this)
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* @param keyPreferences list of preferences per key
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* @return negotiated algorithm
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*/
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SymmetricKeyAlgorithm negotiate(Policy.SymmetricKeyAlgorithmPolicy policy, SymmetricKeyAlgorithm override, List<Set<SymmetricKeyAlgorithm>> keyPreferences);
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static SymmetricKeyAlgorithmNegotiator byPopularity() {
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return new SymmetricKeyAlgorithmNegotiator() {
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@Override
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public SymmetricKeyAlgorithm negotiate(Policy.SymmetricKeyAlgorithmPolicy policy, SymmetricKeyAlgorithm override, List<Set<SymmetricKeyAlgorithm>> preferences) {
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if (override == SymmetricKeyAlgorithm.NULL) {
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throw new IllegalArgumentException("Algorithm override cannot be NULL (plaintext).");
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}
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if (override != null) {
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return override;
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}
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Map<SymmetricKeyAlgorithm, Integer> supportWeight = new LinkedHashMap<>();
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for (Set<SymmetricKeyAlgorithm> keyPreferences : preferences) {
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for (SymmetricKeyAlgorithm preferred : keyPreferences) {
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if (supportWeight.containsKey(preferred)) {
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supportWeight.put(preferred, supportWeight.get(preferred) + 1);
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} else {
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supportWeight.put(preferred, 1);
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}
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}
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}
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List<SymmetricKeyAlgorithm> scoreboard = new ArrayList<>(supportWeight.keySet());
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// Sort scoreboard by descending popularity
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Collections.sort(scoreboard, new Comparator<SymmetricKeyAlgorithm>() {
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@Override
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public int compare(SymmetricKeyAlgorithm t0, SymmetricKeyAlgorithm t1) {
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return -supportWeight.get(t0).compareTo(supportWeight.get(t1));
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}
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});
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for (SymmetricKeyAlgorithm mostWanted : scoreboard) {
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if (policy.isAcceptable(mostWanted)) {
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return mostWanted;
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}
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}
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return policy.getDefaultSymmetricKeyAlgorithm();
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}
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};
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}
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}
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