Fix double verification error neuhalje#66

Nesting inputstreams can result in a child stream reaching its end twice.
For the MDCValidatingInputStream this results in verifying the MDC twice.
PGPEncryptedData#verify doesn't handle being called twice.

Fix with a simple boolean flag to prevent double verification.

src/main/java/name/neuhalfen/projects/crypto/bouncycastle/openpgp/decrypting/MDCValidatingInputStream.java

@@ -13,6 +13,10 @@ final class MDCValidatingInputStream extends FilterInputStream {
   private static final org.slf4j.Logger LOGGER = org.slf4j.LoggerFactory
       .getLogger(MDCValidatingInputStream.class);
 
+  private final PGPPublicKeyEncryptedData pbe;
+
+  private boolean mdcChecked = false;
+
   /**
    * Creates a <code>MDCValidatingInputStream</code> by assigning the  argument
    * <code>inputStream</code> to the field <code>this.inputStream</code> and <code>pbe</code> to <code>this.pbe</code> so as to remember it for
@@ -21,9 +25,6 @@ final class MDCValidatingInputStream extends FilterInputStream {
    * @param inputStream the underlying input stream
    * @param pbe the pgp public key encrypted data to verify message integrity
    */
-
-  private final PGPPublicKeyEncryptedData pbe;
-
   MDCValidatingInputStream(InputStream inputStream, PGPPublicKeyEncryptedData pbe) {
     super(inputStream);
     this.pbe = pbe;
@@ -61,6 +62,11 @@ public int read(@Nonnull byte[] b, int off, int len) throws IOException {
    * @throws IOException Error while reading input stream or if MDC fails
    */
   private void validateMDC() throws IOException {
+    if (mdcChecked) {
+      return;
+    }
+    mdcChecked = true;
+
     try {
       if (pbe.isIntegrityProtected()) {
         if (!pbe.verify()) {

src/test/java/name/neuhalfen/projects/crypto/bouncycastle/openpgp/BuildDecryptionInputStreamAPITest.java

@@ -6,11 +6,12 @@
 import static org.junit.Assume.assumeNotNull;
 import static org.mockito.Mockito.mock;
 
+import java.io.BufferedInputStream;
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.io.InputStream;
-import java.nio.charset.StandardCharsets;
+
 import name.neuhalfen.projects.crypto.bouncycastle.openpgp.keys.keyrings.KeyringConfig;
 import name.neuhalfen.projects.crypto.bouncycastle.openpgp.testtooling.Configs;
 import name.neuhalfen.projects.crypto.bouncycastle.openpgp.testtooling.ExampleMessages;
@@ -144,6 +145,31 @@ public void decryptNoSignatureValidation_withUnsignedData_works() throws Excepti
     }
   }
 
+  @Test()
+  public void decryptNoSignatureValidation_withWrapperStream_works() throws Exception {
+
+    try (InputStream ciphertext = new ByteArrayInputStream(
+            ExampleMessages.IMPORTANT_QUOTE_NOT_SIGNED_NOT_COMPRESSED.getBytes(
+                    "US-ASCII"))) {
+      final InputStream plaintextStream = BouncyGPG.decryptAndVerifyStream()
+              .withConfig(Configs.keyringConfigFromResourceForRecipient())
+              .andIgnoreSignatures()
+              .fromEncryptedInputStream(ciphertext);
+
+      final InputStream wrapperStream = new InputStream() {
+        @Override
+        public int read() throws IOException {
+          return plaintextStream.read();
+        }
+      };
+
+      final String plainText = inputStreamToText(wrapperStream);
+
+      assertThat(plainText, equalTo(ExampleMessages.IMPORTANT_QUOTE_TEXT));
+      plaintextStream.close();
+    }
+  }
+
   @Test(expected = IOException.class)
   public void decryptAndValidateSignature_withUnsignedData_throws() throws Exception {