Frame-at-a-time decryption.

components/net/sf/briar/transport/ConnectionDecrypter.java

@@ -1,14 +1,13 @@
 package net.sf.briar.transport;
 
 import java.io.IOException;
-import java.io.InputStream;
 
 /** Decrypts unauthenticated data received over a connection. */
 interface ConnectionDecrypter {
 
-	/** Returns an input stream from which decrypted data can be read. */
+	/**
-	InputStream getInputStream();
+	 * Reads and decrypts a frame into the given buffer and returns the length
-
+	 * of the decrypted frame, or -1 if no more frames can be read.
-	/** Reads and decrypts the remainder of the current frame. */
+	 */
-	void readFinal(byte[] b) throws IOException;
+	int readFrame(byte[] b) throws IOException;
 }

components/net/sf/briar/transport/ConnectionDecrypterImpl.java

@@ -1,9 +1,10 @@
 package net.sf.briar.transport;
 
+import static net.sf.briar.api.transport.TransportConstants.FRAME_HEADER_LENGTH;
+import static net.sf.briar.api.transport.TransportConstants.MAX_FRAME_LENGTH;
 import static net.sf.briar.util.ByteUtils.MAX_32_BIT_UNSIGNED;
 
 import java.io.EOFException;
-import java.io.FilterInputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.security.GeneralSecurityException;
@@ -11,136 +12,35 @@ import java.security.GeneralSecurityException;
 import javax.crypto.Cipher;
 import javax.crypto.spec.IvParameterSpec;
 
+import net.sf.briar.api.FormatException;
 import net.sf.briar.api.crypto.ErasableKey;
 
-class ConnectionDecrypterImpl extends FilterInputStream
+class ConnectionDecrypterImpl implements ConnectionDecrypter {
-implements ConnectionDecrypter {
 
+	private final InputStream in;
 	private final Cipher frameCipher;
 	private final ErasableKey frameKey;
-	private final byte[] iv, buf;
+	private final int macLength, blockSize;
+	private final byte[] iv;
 
-	private int bufOff = 0, bufLen = 0;
 	private long frame = 0L;
-	private boolean betweenFrames = true;
 
 	ConnectionDecrypterImpl(InputStream in, Cipher frameCipher,
-			ErasableKey frameKey) {
+			ErasableKey frameKey, int macLength) {
-		super(in);
+		this.in = in;
 		this.frameCipher = frameCipher;
 		this.frameKey = frameKey;
-		iv = IvEncoder.encodeIv(0, frameCipher.getBlockSize());
+		this.macLength = macLength;
-		buf = new byte[frameCipher.getBlockSize()];
+		blockSize = frameCipher.getBlockSize();
+		if(blockSize < FRAME_HEADER_LENGTH)
+			throw new IllegalArgumentException();
+		iv = IvEncoder.encodeIv(0, blockSize);
 	}
 
-	public InputStream getInputStream() {
+	public int readFrame(byte[] b) throws IOException {
-		return this;
+		if(b.length < MAX_FRAME_LENGTH) throw new IllegalArgumentException();
-	}
-
-	public void readFinal(byte[] b) throws IOException {
-		try {
-			if(betweenFrames) throw new IllegalStateException();
-			// If we have any plaintext in the buffer, copy it into the frame
-			System.arraycopy(buf, bufOff, b, 0, bufLen);
-			// Read the remainder of the frame
-			int offset = bufLen;
-			while(offset < b.length) {
-				int read = in.read(b, offset, b.length - offset);
-				if(read == -1) break;
-				offset += read;
-			}
-			if(offset < b.length) throw new EOFException(); // Unexpected EOF
-			// Decrypt the remainder of the frame
-			try {
-				int length = b.length - bufLen;
-				int i = frameCipher.doFinal(b, bufLen, length, b, bufLen);
-				if(i < length) throw new RuntimeException();
-			} catch(GeneralSecurityException badCipher) {
-				throw new RuntimeException(badCipher);
-			}
-			bufOff = bufLen = 0;
-			betweenFrames = true;
-		} catch(IOException e) {
-			frameKey.erase();
-			throw e;
-		}
-	}
-
-	@Override
-	public int read() throws IOException {
-		try {
-			if(betweenFrames) initialiseCipher();
-			if(bufLen == 0) {
-				if(!readBlock()) {
-					frameKey.erase();
-					return -1;
-				}
-				bufOff = 0;
-				bufLen = buf.length;
-			}
-			int i = buf[bufOff];
-			bufOff++;
-			bufLen--;
-			return i < 0 ? i + 256 : i;
-		} catch(IOException e) {
-			frameKey.erase();
-			throw e;
-		}
-	}
-
-	@Override
-	public int read(byte[] b) throws IOException {
-		return read(b, 0, b.length);
-	}
-
-	@Override
-	public int read(byte[] b, int off, int len) throws IOException {
-		try {
-			if(betweenFrames) initialiseCipher();
-			if(bufLen == 0) {
-				if(!readBlock()) {
-					frameKey.erase();
-					return -1;
-				}
-				bufOff = 0;
-				bufLen = buf.length;
-			}
-			int length = Math.min(len, bufLen);
-			System.arraycopy(buf, bufOff, b, off, length);
-			bufOff += length;
-			bufLen -= length;
-			return length;
-		} catch(IOException e) {
-			frameKey.erase();
-			throw e;
-		}
-	}
-
-	// Although we're using CTR mode, which doesn't require full blocks of
-	// ciphertext, the cipher still tries to operate a block at a time
-	private boolean readBlock() throws IOException {
-		// Try to read a block of ciphertext
-		int offset = 0;
-		while(offset < buf.length) {
-			int read = in.read(buf, offset, buf.length - offset);
-			if(read == -1) break;
-			offset += read;
-		}
-		if(offset == 0) return false;
-		if(offset < buf.length) throw new EOFException(); // Unexpected EOF
-		// Decrypt the block
-		try {
-			int i = frameCipher.update(buf, 0, offset, buf);
-			if(i < offset) throw new RuntimeException();
-		} catch(GeneralSecurityException badCipher) {
-			throw new RuntimeException(badCipher);
-		}
-		return true;
-	}
-
-	private void initialiseCipher() {
-		assert betweenFrames;
 		if(frame > MAX_32_BIT_UNSIGNED) throw new IllegalStateException();
+		// Initialise the cipher
 		IvEncoder.updateIv(iv, frame);
 		IvParameterSpec ivSpec = new IvParameterSpec(iv);
 		try {
@@ -148,7 +48,52 @@ implements ConnectionDecrypter {
 		} catch(GeneralSecurityException badIvOrKey) {
 			throw new RuntimeException(badIvOrKey);
 		}
-		frame++;
+		try {
-		betweenFrames = false;
+			// Read the first block
+			int offset = 0;
+			while(offset < blockSize) {
+				int read = in.read(b, offset, blockSize - offset);
+				if(read == -1) {
+					if(offset == 0) return -1;
+					if(offset < blockSize) throw new EOFException();
+					break;
+				}
+				offset += read;
+			}
+			// Decrypt the first block
+			try {
+				int decrypted = frameCipher.update(b, 0, blockSize, b);
+				assert decrypted == blockSize;
+			} catch(GeneralSecurityException badCipher) {
+				throw new RuntimeException(badCipher);
+			}
+			// Validate and parse the header
+			int max = MAX_FRAME_LENGTH - FRAME_HEADER_LENGTH - macLength;
+			if(!HeaderEncoder.validateHeader(b, frame, max))
+				throw new FormatException();
+			int payload = HeaderEncoder.getPayloadLength(b);
+			int padding = HeaderEncoder.getPaddingLength(b);
+			int length = FRAME_HEADER_LENGTH + payload + padding + macLength;
+			if(length > MAX_FRAME_LENGTH) throw new FormatException();
+			// Read the remainder of the frame
+			while(offset < length) {
+				int read = in.read(b, offset, length - offset);
+				if(read == -1) throw new EOFException();
+				offset += read;
+			}
+			// Decrypt the remainder of the frame
+			try {
+				int decrypted = frameCipher.doFinal(b, blockSize,
+						length - blockSize, b, blockSize);
+				assert decrypted == length - blockSize;
+			} catch(GeneralSecurityException badCipher) {
+				throw new RuntimeException(badCipher);
+			}
+			frame++;
+			return length;
+		} catch(IOException e) {
+			frameKey.erase();
+			throw e;
+		}
 	}
 }

components/net/sf/briar/transport/ConnectionEncrypter.java

@@ -6,7 +6,7 @@ import java.io.IOException;
 interface ConnectionEncrypter {
 
 	/** Encrypts and writes the given frame. */
-	void writeFrame(byte[] b, int off, int len) throws IOException;
+	void writeFrame(byte[] b, int len) throws IOException;
 
 	/** Flushes the output stream. */
 	void flush() throws IOException;

components/net/sf/briar/transport/ConnectionEncrypterImpl.java

@@ -35,7 +35,7 @@ class ConnectionEncrypterImpl implements ConnectionEncrypter {
 		if(tag.length != TAG_LENGTH) throw new IllegalArgumentException();
 	}
 
-	public void writeFrame(byte[] b, int off, int len) throws IOException {
+	public void writeFrame(byte[] b, int len) throws IOException {
 		try {
 			if(!tagWritten) {
 				out.write(tag);
@@ -47,12 +47,12 @@ class ConnectionEncrypterImpl implements ConnectionEncrypter {
 			IvParameterSpec ivSpec = new IvParameterSpec(iv);
 			try {
 				frameCipher.init(Cipher.ENCRYPT_MODE, frameKey, ivSpec);
-				int encrypted = frameCipher.doFinal(b, off, len, b, off);
+				int encrypted = frameCipher.doFinal(b, 0, len, b, 0);
 				assert encrypted == len;
 			} catch(GeneralSecurityException badCipher) {
 				throw new RuntimeException(badCipher);
 			}
-			out.write(b, off, len);
+			out.write(b, 0, len);
 			capacity -= len;
 			frame++;
 		} catch(IOException e) {

components/net/sf/briar/transport/ConnectionReaderFactoryImpl.java

@@ -46,10 +46,10 @@ class ConnectionReaderFactoryImpl implements ConnectionReaderFactory {
 		ByteUtils.erase(secret);
 		// Create the decrypter
 		Cipher frameCipher = crypto.getFrameCipher();
-		ConnectionDecrypter decrypter = new ConnectionDecrypterImpl(in,
-				frameCipher, frameKey);
-		// Create the reader
 		Mac mac = crypto.getMac();
+		ConnectionDecrypter decrypter = new ConnectionDecrypterImpl(in,
+				frameCipher, frameKey, mac.getMacLength());
+		// Create the reader
 		return new ConnectionReaderImpl(decrypter, mac, macKey);
 	}
 }

components/net/sf/briar/transport/ConnectionReaderImpl.java

@@ -4,12 +4,9 @@ import static net.sf.briar.api.transport.TransportConstants.FRAME_HEADER_LENGTH;
 import static net.sf.briar.api.transport.TransportConstants.MAX_FRAME_LENGTH;
 import static net.sf.briar.util.ByteUtils.MAX_32_BIT_UNSIGNED;
 
-import java.io.EOFException;
-import java.io.FilterInputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.security.InvalidKeyException;
-import java.util.Arrays;
 
 import javax.crypto.Mac;
 
@@ -17,21 +14,18 @@ import net.sf.briar.api.FormatException;
 import net.sf.briar.api.crypto.ErasableKey;
 import net.sf.briar.api.transport.ConnectionReader;
 
-class ConnectionReaderImpl extends FilterInputStream
+class ConnectionReaderImpl extends InputStream implements ConnectionReader {
-implements ConnectionReader {
 
 	private final ConnectionDecrypter decrypter;
 	private final Mac mac;
-	private final int maxPayloadLength;
+	private final int macLength;
-	private final byte[] header, payload, footer;
+	private final byte[] buf;
 
 	private long frame = 0L;
-	private int payloadOff = 0, payloadLen = 0;
+	private int bufOffset = 0, bufLength = 0;
-	private boolean betweenFrames = true;
 
 	ConnectionReaderImpl(ConnectionDecrypter decrypter, Mac mac,
 			ErasableKey macKey) {
-		super(decrypter.getInputStream());
 		this.decrypter = decrypter;
 		this.mac = mac;
 		// Initialise the MAC
@@ -41,11 +35,8 @@ implements ConnectionReader {
 			throw new IllegalArgumentException(e);
 		}
 		macKey.erase();
-		maxPayloadLength =
+		macLength = mac.getMacLength();
-			MAX_FRAME_LENGTH - FRAME_HEADER_LENGTH - mac.getMacLength();
+		buf = new byte[MAX_FRAME_LENGTH];
-		header = new byte[FRAME_HEADER_LENGTH];
-		payload = new byte[maxPayloadLength];
-		footer = new byte[mac.getMacLength()];
 	}
 
 	public InputStream getInputStream() {
@@ -54,12 +45,11 @@ implements ConnectionReader {
 
 	@Override
 	public int read() throws IOException {
-		if(betweenFrames && !readNonEmptyFrame()) return -1;
+		while(bufLength == 0) if(!readFrame()) return -1;
-		int i = payload[payloadOff];
+		int b = buf[bufOffset] & 0xff;
-		payloadOff++;
+		bufOffset++;
-		payloadLen--;
+		bufLength--;
-		if(payloadLen == 0) betweenFrames = true;
+		return b;
-		return i;
 	}
 
 	@Override
@@ -69,69 +59,44 @@ implements ConnectionReader {
 
 	@Override
 	public int read(byte[] b, int off, int len) throws IOException {
-		if(betweenFrames && !readNonEmptyFrame()) return -1;
+		while(bufLength == 0) if(!readFrame()) return -1;
-		len = Math.min(len, payloadLen);
+		len = Math.min(len, bufLength);
-		System.arraycopy(payload, payloadOff, b, off, len);
+		System.arraycopy(buf, bufOffset, b, off, len);
-		payloadOff += len;
+		bufOffset += len;
-		payloadLen -= len;
+		bufLength -= len;
-		if(payloadLen == 0) betweenFrames = true;
 		return len;
 	}
 
-	private boolean readNonEmptyFrame() throws IOException {
+	private boolean readFrame() throws IOException {
-		int payload = 0;
+		assert bufLength == 0;
-		do {
-			payload = readFrame();
-		} while(payload == 0);
-		return payload > 0;
-	}
-
-	private int readFrame() throws IOException {
-		assert betweenFrames;
 		// Don't allow more than 2^32 frames to be read
 		if(frame > MAX_32_BIT_UNSIGNED) throw new IllegalStateException();
-		// Read the header
+		// Read a frame
-		int offset = 0;
+		int length = decrypter.readFrame(buf);
-		while(offset < header.length) {
+		if(length == -1) return false;
-			int read = in.read(header, offset, header.length - offset);
-			if(read == -1) break;
-			offset += read;
-		}
-		if(offset == 0) return -1; // EOF between frames
-		if(offset < header.length) throw new EOFException(); // Unexpected EOF
 		// Check that the frame number is correct and the length is legal
-		if(!HeaderEncoder.validateHeader(header, frame, maxPayloadLength))
+		int max = MAX_FRAME_LENGTH - FRAME_HEADER_LENGTH - macLength;
+		if(!HeaderEncoder.validateHeader(buf, frame, max))
+			throw new FormatException();
+		int payload = HeaderEncoder.getPayloadLength(buf);
+		int padding = HeaderEncoder.getPaddingLength(buf);
+		if(length != FRAME_HEADER_LENGTH + payload + padding + macLength)
 			throw new FormatException();
-		payloadLen = HeaderEncoder.getPayloadLength(header);
-		int paddingLen = HeaderEncoder.getPaddingLength(header);
-		mac.update(header);
-		// Read the payload
-		offset = 0;
-		while(offset < payloadLen) {
-			int read = in.read(payload, offset, payloadLen - offset);
-			if(read == -1) throw new EOFException(); // Unexpected EOF
-			mac.update(payload, offset, read);
-			offset += read;
-		}
-		payloadOff = 0;
-		// Read the padding
-		while(offset < payloadLen + paddingLen) {
-			int read = in.read(payload, offset,
-					payloadLen + paddingLen - offset);
-			if(read == -1) throw new EOFException(); // Unexpected EOF
-			mac.update(payload, offset, read);
-			offset += read;
-		}
 		// Check that the padding is all zeroes
-		for(int i = payloadLen; i < payloadLen + paddingLen; i++) {
+		int paddingStart = FRAME_HEADER_LENGTH + payload;
-			if(payload[i] != 0) throw new FormatException();
+		for(int i = paddingStart; i < paddingStart + padding; i++) {
+			if(buf[i] != 0) throw new FormatException();
 		}
-		// Read the MAC
+		// Check the MAC
+		int macStart = FRAME_HEADER_LENGTH + payload + padding;
+		mac.update(buf, 0, macStart);
 		byte[] expectedMac = mac.doFinal();
-		decrypter.readFinal(footer);
+		for(int i = 0; i < macLength; i++) {
-		if(!Arrays.equals(expectedMac, footer)) throw new FormatException();
+			if(expectedMac[i] != buf[macStart + i]) throw new FormatException();
+		}
+		bufOffset = FRAME_HEADER_LENGTH;
+		bufLength = payload;
 		frame++;
-		if(payloadLen > 0) betweenFrames = false;
+		return true;
-		return payloadLen;
 	}
 }

components/net/sf/briar/transport/ConnectionWriterImpl.java

@@ -101,7 +101,7 @@ class ConnectionWriterImpl extends OutputStream implements ConnectionWriter {
 		} catch(ShortBufferException badMac) {
 			throw new RuntimeException(badMac);
 		}
-		encrypter.writeFrame(buf, 0, bufLength + mac.getMacLength());
+		encrypter.writeFrame(buf, bufLength + mac.getMacLength());
 		bufLength = FRAME_HEADER_LENGTH;
 		frame++;
 	}

test/net/sf/briar/transport/ConnectionDecrypterImplTest.java

@@ -1,6 +1,7 @@
 package net.sf.briar.transport;
 
-import static org.junit.Assert.assertArrayEquals;
+import static net.sf.briar.api.transport.TransportConstants.FRAME_HEADER_LENGTH;
+import static net.sf.briar.api.transport.TransportConstants.MAX_FRAME_LENGTH;
 
 import java.io.ByteArrayInputStream;
 
@@ -8,7 +9,6 @@ import javax.crypto.Cipher;
 import javax.crypto.spec.IvParameterSpec;
 
 import net.sf.briar.BriarTestCase;
-import net.sf.briar.TestUtils;
 import net.sf.briar.api.crypto.CryptoComponent;
 import net.sf.briar.api.crypto.ErasableKey;
 import net.sf.briar.crypto.CryptoModule;
@@ -45,58 +45,40 @@ public class ConnectionDecrypterImplTest extends BriarTestCase {
 	}
 
 	private void testDecryption(boolean initiator) throws Exception {
-		// Calculate the expected plaintext for the first frame
+		// Calculate the ciphertext for the first frame
-		byte[] iv = new byte[frameCipher.getBlockSize()];
+		byte[] plaintext = new byte[FRAME_HEADER_LENGTH + 123 + MAC_LENGTH];
-		byte[] ciphertext = new byte[123];
+		HeaderEncoder.encodeHeader(plaintext, 0L, 123, 0);
-		byte[] ciphertextMac = new byte[MAC_LENGTH];
+		byte[] iv = IvEncoder.encodeIv(0L, frameCipher.getBlockSize());
 		IvParameterSpec ivSpec = new IvParameterSpec(iv);
-		frameCipher.init(Cipher.DECRYPT_MODE, frameKey, ivSpec);
+		frameCipher.init(Cipher.ENCRYPT_MODE, frameKey, ivSpec);
-		byte[] plaintext = new byte[ciphertext.length + ciphertextMac.length];
+		byte[] ciphertext = new byte[plaintext.length];
-		int offset = frameCipher.update(ciphertext, 0, ciphertext.length,
+		frameCipher.doFinal(plaintext, 0, plaintext.length, ciphertext);
-				plaintext);
+		// Calculate the ciphertext for the second frame
-		frameCipher.doFinal(ciphertextMac, 0, ciphertextMac.length, plaintext,
+		byte[] plaintext1 = new byte[FRAME_HEADER_LENGTH + 1234 + MAC_LENGTH];
-				offset);
+		HeaderEncoder.encodeHeader(plaintext1, 1L, 1234, 0);
-		// Calculate the expected plaintext for the second frame
-		byte[] ciphertext1 = new byte[1234];
 		IvEncoder.updateIv(iv, 1L);
 		ivSpec = new IvParameterSpec(iv);
-		frameCipher.init(Cipher.DECRYPT_MODE, frameKey, ivSpec);
+		frameCipher.init(Cipher.ENCRYPT_MODE, frameKey, ivSpec);
-		byte[] plaintext1 = new byte[ciphertext1.length + ciphertextMac.length];
+		byte[] ciphertext1 = new byte[plaintext1.length];
-		offset = frameCipher.update(ciphertext1, 0, ciphertext1.length,
+		frameCipher.doFinal(plaintext1, 0, plaintext1.length, ciphertext1);
-				plaintext1);
-		frameCipher.doFinal(ciphertextMac, 0, ciphertextMac.length, plaintext1,
-				offset);
 		// Concatenate the ciphertexts
 		ByteArrayOutputStream out = new ByteArrayOutputStream();
 		out.write(ciphertext);
-		out.write(ciphertextMac);
 		out.write(ciphertext1);
-		out.write(ciphertextMac);
 		ByteArrayInputStream in = new ByteArrayInputStream(out.toByteArray());
 		// Use a ConnectionDecrypter to decrypt the ciphertext
 		ConnectionDecrypter d = new ConnectionDecrypterImpl(in, frameCipher,
-				frameKey);
+				frameKey, MAC_LENGTH);
 		// First frame
-		byte[] decrypted = new byte[ciphertext.length];
+		byte[] decrypted = new byte[MAX_FRAME_LENGTH];
-		TestUtils.readFully(d.getInputStream(), decrypted);
+		assertEquals(plaintext.length, d.readFrame(decrypted));
-		byte[] decryptedMac = new byte[MAC_LENGTH];
+		for(int i = 0; i < plaintext.length; i++) {
-		d.readFinal(decryptedMac);
+			assertEquals(plaintext[i], decrypted[i]);
+		}
 		// Second frame
-		byte[] decrypted1 = new byte[ciphertext1.length];
+		assertEquals(plaintext1.length, d.readFrame(decrypted));
-		TestUtils.readFully(d.getInputStream(), decrypted1);
+		for(int i = 0; i < plaintext1.length; i++) {
-		byte[] decryptedMac1 = new byte[MAC_LENGTH];
+			assertEquals(plaintext1[i], decrypted[i]);
-		d.readFinal(decryptedMac1);
+		}
-		// Check that the actual plaintext matches the expected plaintext
-		out.reset();
-		out.write(plaintext);
-		out.write(plaintext1);
-		byte[] expected = out.toByteArray();
-		out.reset();
-		out.write(decrypted);
-		out.write(decryptedMac);
-		out.write(decrypted1);
-		out.write(decryptedMac1);
-		byte[] actual = out.toByteArray();
-		assertArrayEquals(expected, actual);
 	}
 }

test/net/sf/briar/transport/ConnectionEncrypterImplTest.java

@@ -69,8 +69,8 @@ public class ConnectionEncrypterImplTest extends BriarTestCase {
 		out.reset();
 		ConnectionEncrypter e = new ConnectionEncrypterImpl(out, Long.MAX_VALUE,
 				tagCipher, frameCipher, tagKey, frameKey);
-		e.writeFrame(plaintext, 0, plaintext.length);
+		e.writeFrame(plaintext, plaintext.length);
-		e.writeFrame(plaintext1, 0, plaintext1.length);
+		e.writeFrame(plaintext1, plaintext1.length);
 		byte[] actual = out.toByteArray();
 		// Check that the actual ciphertext matches the expected ciphertext
 		assertArrayEquals(expected, actual);

test/net/sf/briar/transport/ConnectionReaderImplTest.java

@@ -31,7 +31,7 @@ public class ConnectionReaderImplTest extends TransportTest {
 		mac.doFinal(frame, FRAME_HEADER_LENGTH + payloadLength);
 		// Read the frame
 		ByteArrayInputStream in = new ByteArrayInputStream(frame);
-		ConnectionDecrypter d = new NullConnectionDecrypter(in);
+		ConnectionDecrypter d = new NullConnectionDecrypter(in, macLength);
 		ConnectionReader r = new ConnectionReaderImpl(d, mac, macKey);
 		// There should be no bytes available before EOF
 		assertEquals(-1, r.getInputStream().read());
@@ -49,7 +49,7 @@ public class ConnectionReaderImplTest extends TransportTest {
 		mac.doFinal(frame, FRAME_HEADER_LENGTH + payloadLength);
 		// Read the frame
 		ByteArrayInputStream in = new ByteArrayInputStream(frame);
-		ConnectionDecrypter d = new NullConnectionDecrypter(in);
+		ConnectionDecrypter d = new NullConnectionDecrypter(in, macLength);
 		ConnectionReader r = new ConnectionReaderImpl(d, mac, macKey);
 		// There should be one byte available before EOF
 		assertEquals(0, r.getInputStream().read());
@@ -75,7 +75,7 @@ public class ConnectionReaderImplTest extends TransportTest {
 		out.write(frame1);
 		// Read the first frame
 		ByteArrayInputStream in = new ByteArrayInputStream(out.toByteArray());
-		ConnectionDecrypter d = new NullConnectionDecrypter(in);
+		ConnectionDecrypter d = new NullConnectionDecrypter(in, macLength);
 		ConnectionReader r = new ConnectionReaderImpl(d, mac, macKey);
 		byte[] read = new byte[maxPayloadLength];
 		TestUtils.readFully(r.getInputStream(), read);
@@ -109,7 +109,7 @@ public class ConnectionReaderImplTest extends TransportTest {
 		out.write(frame1);
 		// Read the first frame
 		ByteArrayInputStream in = new ByteArrayInputStream(out.toByteArray());
-		ConnectionDecrypter d = new NullConnectionDecrypter(in);
+		ConnectionDecrypter d = new NullConnectionDecrypter(in, macLength);
 		ConnectionReader r = new ConnectionReaderImpl(d, mac, macKey);
 		byte[] read = new byte[maxPayloadLength - paddingLength];
 		TestUtils.readFully(r.getInputStream(), read);
@@ -135,7 +135,7 @@ public class ConnectionReaderImplTest extends TransportTest {
 		mac.doFinal(frame, FRAME_HEADER_LENGTH + payloadLength + paddingLength);
 		// Read the frame
 		ByteArrayInputStream in = new ByteArrayInputStream(frame);
-		ConnectionDecrypter d = new NullConnectionDecrypter(in);
+		ConnectionDecrypter d = new NullConnectionDecrypter(in, macLength);
 		ConnectionReader r = new ConnectionReaderImpl(d, mac, macKey);
 		// The non-zero padding should be rejected
 		try {
@@ -167,7 +167,7 @@ public class ConnectionReaderImplTest extends TransportTest {
 		out.write(frame1);
 		// Read the frames
 		ByteArrayInputStream in = new ByteArrayInputStream(out.toByteArray());
-		ConnectionDecrypter d = new NullConnectionDecrypter(in);
+		ConnectionDecrypter d = new NullConnectionDecrypter(in, macLength);
 		ConnectionReader r = new ConnectionReaderImpl(d, mac, macKey);
 		byte[] read = new byte[payloadLength];
 		TestUtils.readFully(r.getInputStream(), read);
@@ -191,7 +191,7 @@ public class ConnectionReaderImplTest extends TransportTest {
 		frame[12] ^= 1;
 		// Try to read the frame - not a single byte should be read
 		ByteArrayInputStream in = new ByteArrayInputStream(frame);
-		ConnectionDecrypter d = new NullConnectionDecrypter(in);
+		ConnectionDecrypter d = new NullConnectionDecrypter(in, macLength);
 		ConnectionReader r = new ConnectionReaderImpl(d, mac, macKey);
 		try {
 			r.getInputStream().read();
@@ -213,7 +213,7 @@ public class ConnectionReaderImplTest extends TransportTest {
 		frame[17] ^= 1;
 		// Try to read the frame - not a single byte should be read
 		ByteArrayInputStream in = new ByteArrayInputStream(frame);
-		ConnectionDecrypter d = new NullConnectionDecrypter(in);
+		ConnectionDecrypter d = new NullConnectionDecrypter(in, macLength);
 		ConnectionReader r = new ConnectionReaderImpl(d, mac, macKey);
 		try {
 			r.getInputStream().read();

test/net/sf/briar/transport/FrameReadWriteTest.java

@@ -90,7 +90,7 @@ public class FrameReadWriteTest extends BriarTestCase {
 		assertTrue(TagEncoder.validateTag(tag, 0, tagCipher, tagKey));
 		// Read the frames back
 		ConnectionDecrypter decrypter = new ConnectionDecrypterImpl(in,
-				frameCipher, frameKey);
+				frameCipher, frameKey, mac.getMacLength());
 		ConnectionReader reader = new ConnectionReaderImpl(decrypter, mac,
 				macKey);
 		InputStream in1 = reader.getInputStream();

test/net/sf/briar/transport/NullConnectionDecrypter.java

@@ -1,29 +1,48 @@
 package net.sf.briar.transport;
 
+import static net.sf.briar.api.transport.TransportConstants.FRAME_HEADER_LENGTH;
+import static net.sf.briar.api.transport.TransportConstants.MAX_FRAME_LENGTH;
+
 import java.io.EOFException;
 import java.io.IOException;
 import java.io.InputStream;
 
+import net.sf.briar.api.FormatException;
+
 /** A ConnectionDecrypter that performs no decryption. */
 class NullConnectionDecrypter implements ConnectionDecrypter {
 
 	private final InputStream in;
+	private final int macLength;
 
-	NullConnectionDecrypter(InputStream in) {
+	NullConnectionDecrypter(InputStream in, int macLength) {
 		this.in = in;
+		this.macLength = macLength;
 	}
 
-	public InputStream getInputStream() {
+	public int readFrame(byte[] b) throws IOException {
-		return in;
+		if(b.length < MAX_FRAME_LENGTH) throw new IllegalArgumentException();
-	}
+		// Read the header to determine the frame length
-
+		int offset = 0, length = FRAME_HEADER_LENGTH;
-	public void readFinal(byte[] mac) throws IOException {
+		while(offset < length) {
-		int offset = 0;
+			int read = in.read(b, offset, length - offset);
-		while(offset < mac.length) {
+			if(read == -1) {
-			int read = in.read(mac, offset, mac.length - offset);
+				if(offset == 0) return -1;
-			if(read == -1) break;
+				throw new EOFException();
+			}
 			offset += read;
 		}
-		if(offset < mac.length) throw new EOFException();
+		// Parse the header
+		int payload = HeaderEncoder.getPayloadLength(b);
+		int padding = HeaderEncoder.getPaddingLength(b);
+		length = FRAME_HEADER_LENGTH + payload + padding + macLength;
+		if(length > MAX_FRAME_LENGTH) throw new FormatException();
+		// Read the remainder of the frame
+		while(offset < length) {
+			int read = in.read(b, offset, length - offset);
+			if(read == -1) throw new EOFException();
+			offset += read;
+		}
+		return length;
 	}
 }

test/net/sf/briar/transport/NullConnectionEncrypter.java

@@ -20,8 +20,8 @@ class NullConnectionEncrypter implements ConnectionEncrypter {
 		this.capacity = capacity;
 	}
 
-	public void writeFrame(byte[] b, int off, int len) throws IOException {
+	public void writeFrame(byte[] b, int len) throws IOException {
-		out.write(b, off, len);
+		out.write(b, 0, len);
 		capacity -= len;
 	}