Implement detection of non-UTF8 passwords

sop-java-picocli/src/main/java/sop/cli/picocli/FileUtil.java

@@ -10,9 +10,9 @@ import java.io.FileInputStream;
 import java.io.FileNotFoundException;
 import java.io.InputStream;
 import java.io.IOException;
-import java.nio.charset.Charset;
 
 import sop.exception.SOPGPException;
+import sop.util.UTF8Util;
 
 public class FileUtil {
 
@@ -106,7 +106,7 @@ public class FileUtil {
             while ((read = inputStream.read(buf)) != -1) {
                 byteOut.write(buf, 0, read);
             }
-            return new String(byteOut.toByteArray(), Charset.forName("UTF8"));
+            return UTF8Util.decodeUTF8(byteOut.toByteArray());
         } finally {
             inputStream.close();
         }

sop-java/src/main/java/sop/exception/SOPGPException.java

@@ -4,8 +4,6 @@
 
 package sop.exception;
 
-import java.io.IOException;
-
 public abstract class SOPGPException extends RuntimeException {
 
     public SOPGPException() {
@@ -134,10 +132,6 @@ public abstract class SOPGPException extends RuntimeException {
             super();
         }
 
-        public PasswordNotHumanReadable(String message, IOException e) {
-            super(message, e);
-        }
-
         @Override
         public int getExitCode() {
             return EXIT_CODE;

sop-java/src/main/java/sop/util/UTF8Util.java

@@ -0,0 +1,39 @@
+// SPDX-FileCopyrightText: 2022 Paul Schaub <vanitasvitae@fsfe.org>
+//
+// SPDX-License-Identifier: Apache-2.0
+
+package sop.util;
+
+import sop.exception.SOPGPException;
+
+import java.nio.ByteBuffer;
+import java.nio.CharBuffer;
+import java.nio.charset.CharacterCodingException;
+import java.nio.charset.Charset;
+import java.nio.charset.CharsetDecoder;
+import java.nio.charset.CodingErrorAction;
+
+public class UTF8Util {
+
+    private static final CharsetDecoder UTF8Decoder = Charset.forName("UTF8")
+            .newDecoder()
+            .onUnmappableCharacter(CodingErrorAction.REPORT)
+            .onMalformedInput(CodingErrorAction.REPORT);
+
+    /**
+     * Detect non-valid UTF8 data.
+     *
+     * @see <a href="https://stackoverflow.com/a/1471193">ante on StackOverflow</a>
+     * @param data
+     * @return
+     */
+    public static String decodeUTF8(byte[] data) {
+        ByteBuffer byteBuffer = ByteBuffer.wrap(data);
+        try {
+            CharBuffer charBuffer = UTF8Decoder.decode(byteBuffer);
+            return charBuffer.toString();
+        } catch (CharacterCodingException e) {
+            throw new SOPGPException.PasswordNotHumanReadable();
+        }
+    }
+}

sop-java/src/test/java/sop/util/UTF8UtilTest.java

@@ -0,0 +1,39 @@
+// SPDX-FileCopyrightText: 2022 Paul Schaub <vanitasvitae@fsfe.org>
+//
+// SPDX-License-Identifier: Apache-2.0
+
+package sop.util;
+
+import org.junit.jupiter.api.Test;
+import sop.exception.SOPGPException;
+
+import java.nio.charset.StandardCharsets;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+public class UTF8UtilTest {
+
+    @Test
+    public void testValidUtf8Decoding() {
+        String utf8String = "Hello, World\n";
+        String decoded = UTF8Util.decodeUTF8(utf8String.getBytes(StandardCharsets.UTF_8));
+
+        assertEquals(utf8String, decoded);
+    }
+
+    /**
+     * Test detection of non-uft8 data.
+     * @see <a href="https://www.cl.cam.ac.uk/~mgk25/ucs/examples/UTF-8-test.txt">
+     *     Markus Kuhn's UTF8 decoder capability and stress test file</a>
+     */
+    @Test
+    public void testInvalidUtf8StringThrows() {
+        assertThrows(SOPGPException.PasswordNotHumanReadable.class,
+                () -> UTF8Util.decodeUTF8(new byte[] {(byte) 0xa0, (byte) 0xa1}));
+        assertThrows(SOPGPException.PasswordNotHumanReadable.class,
+                () -> UTF8Util.decodeUTF8(new byte[] {(byte) 0xc0, (byte) 0xaf}));
+        assertThrows(SOPGPException.PasswordNotHumanReadable.class,
+                () -> UTF8Util.decodeUTF8(new byte[] {(byte) 0x80, (byte) 0xbf}));
+    }
+}