Add option to force handling of data as non-openpgp

pgpainless-core/src/main/java/org/pgpainless/decryption_verification/ConsumerOptions.java

@@ -36,6 +36,7 @@ public class ConsumerOptions {
 
 
     private boolean ignoreMDCErrors = false;
+    private boolean forceNonOpenPgpData = false;
 
     private Date verifyNotBefore = null;
     private Date verifyNotAfter = new Date();
@@ -296,6 +297,21 @@ public class ConsumerOptions {
         return ignoreMDCErrors;
     }
 
+    /**
+     * Force PGPainless to handle the data provided by the {@link InputStream} as non-OpenPGP data.
+     * This workaround might come in handy if PGPainless accidentally mistakes the data for binary OpenPGP data.
+     *
+     * @return options
+     */
+    public ConsumerOptions forceNonOpenPgpData() {
+        this.forceNonOpenPgpData = true;
+        return this;
+    }
+
+    boolean isForceNonOpenPgpData() {
+        return forceNonOpenPgpData;
+    }
+
     /**
      * Specify the {@link MissingKeyPassphraseStrategy}.
      * This strategy defines, how missing passphrases for unlocking secret keys are handled.

pgpainless-core/src/main/java/org/pgpainless/decryption_verification/DecryptionStreamFactory.java

@@ -134,7 +134,7 @@ public final class DecryptionStreamFactory {
         PGPObjectFactory objectFactory;
 
         // Non-OpenPGP data. We are probably verifying detached signatures
-        if (openPgpIn.isNonOpenPgp()) {
+        if (openPgpIn.isNonOpenPgp() || options.isForceNonOpenPgpData()) {
             outerDecodingStream = openPgpIn;
             pgpInStream = wrapInVerifySignatureStream(outerDecodingStream, null);
             return new DecryptionStream(pgpInStream, resultBuilder, integrityProtectedEncryptedInputStream, null);

pgpainless-core/src/main/java/org/pgpainless/decryption_verification/OpenPgpInputStream.java

@@ -18,7 +18,7 @@ public class OpenPgpInputStream extends BufferedInputStream {
     private static final byte[] ARMOR_HEADER = "-----BEGIN PGP ".getBytes(Charset.forName("UTF8"));
 
     // Buffer beginning bytes of the data
-    public static final int MAX_BUFFER_SIZE = 8192;
+    public static final int MAX_BUFFER_SIZE = 8192 * 2;
 
     private final byte[] buffer;
     private final int bufferLen;
@@ -53,6 +53,14 @@ public class OpenPgpInputStream extends BufferedInputStream {
         return false;
     }
 
+    /**
+     * This method is still brittle.
+     * Basically we try to parse OpenPGP packets from the buffer.
+     * If we run into exceptions, then we know that the data is non-OpenPGP'ish.
+     *
+     * This breaks down though if we read plausible garbage where the data accidentally makes sense,
+     * or valid, yet incomplete packets (remember, we are still only working on a portion of the data).
+     */
     private void determineIsBinaryOpenPgp() {
         if (bufferLen == -1) {
             // Empty data
@@ -62,47 +70,24 @@ public class OpenPgpInputStream extends BufferedInputStream {
         try {
             ByteArrayInputStream bufferIn = new ByteArrayInputStream(buffer, 0, bufferLen);
             PGPObjectFactory objectFactory = ImplementationFactory.getInstance().getPGPObjectFactory(bufferIn);
+
+            boolean containsPackets = false;
             while (objectFactory.nextObject() != null) {
-                // read all packets in buffer
+                containsPackets = true;
+                // read all packets in buffer - hope to confirm invalid data via thrown IOExceptions
             }
-            containsOpenPgpPackets = true;
+            containsOpenPgpPackets = containsPackets;
+
         } catch (IOException e) {
-            if (e.getMessage().contains("premature end of stream in PartialInputStream")) {
-                // We *probably* hit valid, but large OpenPGP data
-                // This is not an optimal way of determining the nature of data, but probably the best
-                // we can get from BC.
-                containsOpenPgpPackets = true;
-            }
-            // else: seemingly random, non-OpenPGP data
-        }
-    }
+            String msg = e.getMessage();
 
-    private boolean startsWith(byte[] bytes, byte[] subsequence, int bufferLen) {
-        return indexOfSubsequence(bytes, subsequence, bufferLen) == 0;
-    }
+            // If true, we *probably* hit valid, but large OpenPGP data (not sure though) :/
+            // Otherwise we hit garbage and can be sure that this is no OpenPGP data \o/
+            containsOpenPgpPackets = (msg != null && msg.contains("premature end of stream in PartialInputStream"));
 
-    private int indexOfSubsequence(byte[] bytes, byte[] subsequence, int bufferLen) {
-        if (bufferLen == -1) {
-            return -1;
+            // This is not an optimal way of determining the nature of data, but probably the best
+            // we can do :/
         }
-        // Naive implementation
-        // TODO: Could be improved by using e.g. Knuth-Morris-Pratt algorithm.
-        for (int i = 0; i < bufferLen; i++) {
-            if ((i + subsequence.length) <= bytes.length) {
-                boolean found = true;
-                for (int j = 0; j < subsequence.length; j++) {
-                    if (bytes[i + j] != subsequence[j]) {
-                        found = false;
-                        break;
-                    }
-                }
-
-                if (found) {
-                    return i;
-                }
-            }
-        }
-        return -1;
     }
 
     private boolean startsWithIgnoringWhitespace(byte[] bytes, byte[] subsequence, int bufferLen) {