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2411e2008b
authenticate each frame before parsing its contents. Each connection starts with a tag, followed by any number of frames, each starting with the frame number (32 bits) and payload length (16 bits), and ending with a MAC (256 bits). Tags have the following format: 32 bits reserved, 16 bits for the transport ID, 32 bits for the connection number, 32 bits (set to zero in the tag) for the frame number, and 16 bits (set to zero in the tag) for the block number. The tag is encrypted with the tag key in ECB mode. Frame numbers for each connection must start from zero and must be contiguous and strictly increasing. Each frame is encrypted with the frame key in CTR mode, using the plaintext tag with the appropriate frame number to initialise the counter. The maximum frame size is 64 KiB, including header and footer. The maximum amount of data that can be sent over a connection is 2^32 frames - roughly 2^48 bytes, or 8 terabytes, with the maximum frame size of 64 KiB. If that isn't sufficient we can add another 16 bits to the frame counter.
108 lines
3.0 KiB
Java
108 lines
3.0 KiB
Java
package net.sf.briar.transport;
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import static net.sf.briar.api.transport.TransportConstants.MAX_FRAME_LENGTH;
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import static net.sf.briar.util.ByteUtils.MAX_32_BIT_UNSIGNED;
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import java.io.EOFException;
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import java.io.FilterInputStream;
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import java.io.IOException;
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import java.io.InputStream;
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import java.util.Arrays;
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import javax.crypto.Mac;
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import net.sf.briar.api.FormatException;
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import net.sf.briar.api.transport.ConnectionReader;
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import net.sf.briar.util.ByteUtils;
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class ConnectionReaderImpl extends FilterInputStream
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implements ConnectionReader {
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private final ConnectionDecrypter decrypter;
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private final Mac mac;
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private final int maxPayloadLength;
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private final byte[] header, payload, footer;
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private long frame = 0L;
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private int payloadOff = 0, payloadLen = 0;
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private boolean betweenFrames = true;
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ConnectionReaderImpl(ConnectionDecrypter decrypter, Mac mac) {
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super(decrypter.getInputStream());
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this.decrypter = decrypter;
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this.mac = mac;
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maxPayloadLength = MAX_FRAME_LENGTH - 6 - mac.getMacLength();
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header = new byte[6];
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payload = new byte[maxPayloadLength];
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footer = new byte[mac.getMacLength()];
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}
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public InputStream getInputStream() {
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return this;
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}
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@Override
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public int read() throws IOException {
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if(betweenFrames && !readFrame()) return -1;
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int i = payload[payloadOff];
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payloadOff++;
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payloadLen--;
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if(payloadLen == 0) betweenFrames = true;
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return i;
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}
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@Override
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public int read(byte[] b) throws IOException {
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return read(b, 0, b.length);
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}
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@Override
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public int read(byte[] b, int off, int len) throws IOException {
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if(betweenFrames && !readFrame()) return -1;
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len = Math.min(len, payloadLen);
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System.arraycopy(payload, payloadOff, b, off, len);
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payloadOff += len;
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payloadLen -= len;
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if(payloadLen == 0) betweenFrames = true;
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return len;
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}
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private boolean readFrame() throws IOException {
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assert betweenFrames;
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// Read the header
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if(frame > MAX_32_BIT_UNSIGNED) throw new IllegalStateException();
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int offset = 0;
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while(offset < header.length) {
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int read = in.read(header, offset, header.length - offset);
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if(read == -1) break;
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offset += read;
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}
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if(offset == 0) return false; // EOF between frames
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if(offset < header.length) throw new EOFException(); // Unexpected EOF
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mac.update(header);
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// Check that the frame has the expected frame number
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if(ByteUtils.readUint32(header, 0) != frame)
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throw new FormatException();
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// Check that the payload length is legal
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payloadLen = ByteUtils.readUint16(header, 4);
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if(payloadLen == 0 || payloadLen > maxPayloadLength)
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throw new FormatException();
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frame++;
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// Read the payload
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offset = 0;
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while(offset < payloadLen) {
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int read = in.read(payload, offset, payloadLen - offset);
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if(read == -1) throw new EOFException(); // Unexpected EOF
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mac.update(payload, offset, read);
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offset += read;
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}
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payloadOff = 0;
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// Read the MAC
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byte[] expectedMac = mac.doFinal();
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decrypter.readMac(footer);
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if(!Arrays.equals(expectedMac, footer)) throw new FormatException();
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betweenFrames = false;
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return true;
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}
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}
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