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Separate out syntax logic
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parent
798e68e87f
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6 changed files with 189 additions and 156 deletions
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// SPDX-FileCopyrightText: 2022 Paul Schaub <vanitasvitae@fsfe.org>
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//
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// SPDX-License-Identifier: Apache-2.0
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package org.pgpainless.decryption_verification.syntax_check;
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import org.pgpainless.exception.MalformedOpenPgpMessageException;
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public class OpenPgpMessageSyntax implements Syntax {
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@Override
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public Transition transition(State from, InputAlphabet input, StackAlphabet stackItem)
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throws MalformedOpenPgpMessageException {
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switch (from) {
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case OpenPgpMessage:
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return fromOpenPgpMessage(input, stackItem);
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case LiteralMessage:
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return fromLiteralMessage(input, stackItem);
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case CompressedMessage:
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return fromCompressedMessage(input, stackItem);
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case EncryptedMessage:
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return fromEncryptedMessage(input, stackItem);
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case Valid:
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return fromValid(input, stackItem);
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}
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throw new MalformedOpenPgpMessageException(from, input, stackItem);
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}
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Transition fromOpenPgpMessage(InputAlphabet input, StackAlphabet stackItem)
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throws MalformedOpenPgpMessageException {
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if (stackItem != StackAlphabet.msg) {
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throw new MalformedOpenPgpMessageException(State.OpenPgpMessage, input, stackItem);
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}
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switch (input) {
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case LiteralData:
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return new Transition(State.LiteralMessage);
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case Signature:
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return new Transition(State.OpenPgpMessage, StackAlphabet.msg);
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case OnePassSignature:
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return new Transition(State.OpenPgpMessage, StackAlphabet.ops, StackAlphabet.msg);
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case CompressedData:
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return new Transition(State.CompressedMessage);
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case EncryptedData:
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return new Transition(State.EncryptedMessage);
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case EndOfSequence:
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default:
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throw new MalformedOpenPgpMessageException(State.OpenPgpMessage, input, stackItem);
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}
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}
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Transition fromLiteralMessage(InputAlphabet input, StackAlphabet stackItem)
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throws MalformedOpenPgpMessageException {
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switch (input) {
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case Signature:
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if (stackItem == StackAlphabet.ops) {
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return new Transition(State.LiteralMessage);
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}
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break;
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case EndOfSequence:
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if (stackItem == StackAlphabet.terminus) {
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return new Transition(State.Valid);
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}
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break;
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}
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throw new MalformedOpenPgpMessageException(State.LiteralMessage, input, stackItem);
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}
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Transition fromCompressedMessage(InputAlphabet input, StackAlphabet stackItem)
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throws MalformedOpenPgpMessageException {
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switch (input) {
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case Signature:
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if (stackItem == StackAlphabet.ops) {
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return new Transition(State.CompressedMessage);
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}
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break;
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case EndOfSequence:
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if (stackItem == StackAlphabet.terminus) {
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return new Transition(State.Valid);
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}
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break;
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}
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throw new MalformedOpenPgpMessageException(State.CompressedMessage, input, stackItem);
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}
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Transition fromEncryptedMessage(InputAlphabet input, StackAlphabet stackItem)
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throws MalformedOpenPgpMessageException {
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switch (input) {
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case Signature:
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if (stackItem == StackAlphabet.ops) {
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return new Transition(State.EncryptedMessage);
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}
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break;
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case EndOfSequence:
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if (stackItem == StackAlphabet.terminus) {
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return new Transition(State.Valid);
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}
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break;
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}
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throw new MalformedOpenPgpMessageException(State.EncryptedMessage, input, stackItem);
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}
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Transition fromValid(InputAlphabet input, StackAlphabet stackItem)
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throws MalformedOpenPgpMessageException {
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throw new MalformedOpenPgpMessageException(State.Valid, input, stackItem);
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}
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}
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@ -14,177 +14,31 @@ import java.util.List;
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import java.util.Stack;
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import static org.pgpainless.decryption_verification.syntax_check.StackAlphabet.msg;
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import static org.pgpainless.decryption_verification.syntax_check.StackAlphabet.ops;
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import static org.pgpainless.decryption_verification.syntax_check.StackAlphabet.terminus;
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public class PDA {
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private static final Logger LOGGER = LoggerFactory.getLogger(PDA.class);
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/**
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* Set of states of the automaton.
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* Each state defines its valid transitions in their {@link State#transition(InputAlphabet, PDA)} method.
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*/
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public enum State {
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OpenPgpMessage {
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@Override
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State transition(InputAlphabet input, PDA automaton) throws MalformedOpenPgpMessageException {
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StackAlphabet stackItem = automaton.popStack();
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if (stackItem != msg) {
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throw new MalformedOpenPgpMessageException(this, input, stackItem);
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}
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switch (input) {
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case LiteralData:
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return LiteralMessage;
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case Signature:
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automaton.pushStack(msg);
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return OpenPgpMessage;
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case OnePassSignature:
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automaton.pushStack(ops);
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automaton.pushStack(msg);
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return OpenPgpMessage;
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case CompressedData:
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return CompressedMessage;
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case EncryptedData:
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return EncryptedMessage;
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case EndOfSequence:
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default:
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throw new MalformedOpenPgpMessageException(this, input, stackItem);
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}
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}
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},
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LiteralMessage {
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@Override
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State transition(InputAlphabet input, PDA automaton) throws MalformedOpenPgpMessageException {
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StackAlphabet stackItem = automaton.popStack();
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switch (input) {
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case Signature:
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if (stackItem == ops) {
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return LiteralMessage;
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} else {
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throw new MalformedOpenPgpMessageException(this, input, stackItem);
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}
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case EndOfSequence:
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if (stackItem == terminus && automaton.stack.isEmpty()) {
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return Valid;
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} else {
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throw new MalformedOpenPgpMessageException(this, input, stackItem);
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}
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case LiteralData:
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case OnePassSignature:
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case CompressedData:
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case EncryptedData:
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default:
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throw new MalformedOpenPgpMessageException(this, input, stackItem);
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}
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}
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},
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CompressedMessage {
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@Override
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State transition(InputAlphabet input, PDA automaton) throws MalformedOpenPgpMessageException {
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StackAlphabet stackItem = automaton.popStack();
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switch (input) {
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case Signature:
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if (stackItem == ops) {
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return CompressedMessage;
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} else {
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throw new MalformedOpenPgpMessageException(this, input, stackItem);
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}
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case EndOfSequence:
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if (stackItem == terminus && automaton.stack.isEmpty()) {
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return Valid;
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} else {
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throw new MalformedOpenPgpMessageException(this, input, stackItem);
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}
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case LiteralData:
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case OnePassSignature:
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case CompressedData:
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case EncryptedData:
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default:
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throw new MalformedOpenPgpMessageException(this, input, stackItem);
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}
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}
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},
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EncryptedMessage {
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@Override
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State transition(InputAlphabet input, PDA automaton) throws MalformedOpenPgpMessageException {
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StackAlphabet stackItem = automaton.popStack();
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switch (input) {
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case Signature:
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if (stackItem == ops) {
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return EncryptedMessage;
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} else {
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throw new MalformedOpenPgpMessageException(this, input, stackItem);
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}
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case EndOfSequence:
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if (stackItem == terminus && automaton.stack.isEmpty()) {
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return Valid;
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} else {
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throw new MalformedOpenPgpMessageException(this, input, stackItem);
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}
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case LiteralData:
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case OnePassSignature:
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case CompressedData:
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case EncryptedData:
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default:
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throw new MalformedOpenPgpMessageException(this, input, stackItem);
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}
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}
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},
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Valid {
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@Override
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State transition(InputAlphabet input, PDA automaton) throws MalformedOpenPgpMessageException {
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throw new MalformedOpenPgpMessageException(this, input, null);
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}
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},
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;
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/**
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* Pop the automatons stack and transition to another state.
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* If no valid transition from the current state is available given the popped stack item and input symbol,
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* a {@link MalformedOpenPgpMessageException} is thrown.
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* Otherwise, the stack is manipulated according to the valid transition and the new state is returned.
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*
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* @param input input symbol
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* @param automaton automaton
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* @return new state of the automaton
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* @throws MalformedOpenPgpMessageException in case of an illegal input symbol
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*/
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abstract State transition(InputAlphabet input, PDA automaton) throws MalformedOpenPgpMessageException;
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}
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private final Stack<StackAlphabet> stack = new Stack<>();
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private final List<InputAlphabet> inputs = new ArrayList<>(); // keep track of inputs for debugging / error reporting
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private State state;
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private Syntax syntax = new OpenPgpMessageSyntax();
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public PDA() {
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state = State.OpenPgpMessage;
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stack.push(terminus);
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stack.push(msg);
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pushStack(terminus);
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pushStack(msg);
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}
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public void next(InputAlphabet input) throws MalformedOpenPgpMessageException {
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try {
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state = state.transition(input, this);
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Transition transition = syntax.transition(state, input, popStack());
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inputs.add(input);
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state = transition.getNewState();
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for (StackAlphabet item : transition.getPushedItems()) {
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pushStack(item);
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}
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} catch (MalformedOpenPgpMessageException e) {
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MalformedOpenPgpMessageException wrapped = new MalformedOpenPgpMessageException("Malformed message: After reading stream " + Arrays.toString(inputs.toArray()) +
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", token '" + input + "' is unexpected and illegal.", e);
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@ -230,6 +84,9 @@ public class PDA {
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* @return stack item
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*/
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private StackAlphabet popStack() {
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if (stack.isEmpty()) {
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return null;
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}
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return stack.pop();
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}
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@ -0,0 +1,16 @@
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// SPDX-FileCopyrightText: 2022 Paul Schaub <vanitasvitae@fsfe.org>
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//
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// SPDX-License-Identifier: Apache-2.0
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package org.pgpainless.decryption_verification.syntax_check;
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/**
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* Set of states of the automaton.
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*/
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public enum State {
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OpenPgpMessage,
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LiteralMessage,
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CompressedMessage,
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EncryptedMessage,
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Valid
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}
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@ -0,0 +1,13 @@
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// SPDX-FileCopyrightText: 2022 Paul Schaub <vanitasvitae@fsfe.org>
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//
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// SPDX-License-Identifier: Apache-2.0
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package org.pgpainless.decryption_verification.syntax_check;
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import org.pgpainless.exception.MalformedOpenPgpMessageException;
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public interface Syntax {
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Transition transition(State from, InputAlphabet inputAlphabet, StackAlphabet stackItem)
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throws MalformedOpenPgpMessageException;
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}
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@ -0,0 +1,28 @@
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// SPDX-FileCopyrightText: 2022 Paul Schaub <vanitasvitae@fsfe.org>
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//
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// SPDX-License-Identifier: Apache-2.0
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package org.pgpainless.decryption_verification.syntax_check;
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import java.util.ArrayList;
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import java.util.Arrays;
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import java.util.List;
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public class Transition {
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private final List<StackAlphabet> pushedItems = new ArrayList<>();
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private final State newState;
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public Transition(State newState, StackAlphabet... pushedItems) {
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this.newState = newState;
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this.pushedItems.addAll(Arrays.asList(pushedItems));
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}
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public State getNewState() {
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return newState;
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}
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public List<StackAlphabet> getPushedItems() {
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return new ArrayList<>(pushedItems);
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}
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}
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@ -5,8 +5,8 @@
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package org.pgpainless.exception;
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import org.pgpainless.decryption_verification.syntax_check.InputAlphabet;
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import org.pgpainless.decryption_verification.syntax_check.PDA;
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import org.pgpainless.decryption_verification.syntax_check.StackAlphabet;
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import org.pgpainless.decryption_verification.syntax_check.State;
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/**
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* Exception that gets thrown if the OpenPGP message is malformed.
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super(message);
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}
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public MalformedOpenPgpMessageException(PDA.State state, InputAlphabet input, StackAlphabet stackItem) {
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public MalformedOpenPgpMessageException(State state, InputAlphabet input, StackAlphabet stackItem) {
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this("There is no legal transition from state '" + state + "' for input '" + input + "' when '" + stackItem + "' is on top of the stack.");
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}
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