DTLS 1.3 reliable handshake (RFC 9147 sections 5.8 and 7), part 2 of 5 for #1468; closes #1487

tls/src/main/java/org/bouncycastle/tls/AbstractTlsContext.java

@@ -289,8 +289,9 @@ else if (!TlsUtils.isValidUint16(context.length))
             TlsHash exporterHash = getCrypto().createHash(cryptoHashAlgorithm);
             byte[] emptyTranscriptHash = exporterHash.calculateHash();
 
-            TlsSecret exporterSecret = TlsUtils.deriveSecret(getSecurityParametersConnection(), secret, asciiLabel,
-                emptyTranscriptHash);
+            SecurityParameters sp = getSecurityParametersConnection();
+
+            TlsSecret exporterSecret = TlsUtils.deriveSecret(sp, secret, asciiLabel, emptyTranscriptHash);
 
             byte[] exporterContext = emptyTranscriptHash;
             if (context.length > 0)
@@ -299,8 +300,12 @@ else if (!TlsUtils.isValidUint16(context.length))
                 exporterContext = exporterHash.calculateHash();
             }
 
+            // RFC 9147 5.9. DTLS 1.3 derives with the "dtls13" label prefix rather than TLS 1.3's "tls13 ".
+            boolean isDTLS = sp.getNegotiatedVersion().isDTLS();
+
             return TlsCryptoUtils
-                .hkdfExpandLabel(exporterSecret, cryptoHashAlgorithm, "exporter", exporterContext, length).extract();
+                .hkdfExpandLabel(exporterSecret, cryptoHashAlgorithm, "exporter", exporterContext, length, isDTLS)
+                .extract();
         }
         catch (IOException e)
         {

tls/src/main/java/org/bouncycastle/tls/ContentType.java

@@ -11,6 +11,8 @@ public class ContentType
     public static final short application_data = 23;
     public static final short heartbeat = 24;
     public static final short tls12_cid = 25;
+    /** RFC 9147 7.1 */
+    public static final short ack = 26;
 
     public static String getName(short contentType)
     {
@@ -27,7 +29,9 @@ public static String getName(short contentType)
         case heartbeat:
             return "heartbeat";
         case tls12_cid:
-            return "tls12_cid";            
+            return "tls12_cid";
+        case ack:
+            return "ack";
         default:
             return "UNKNOWN";
         }

tls/src/main/java/org/bouncycastle/tls/DTLS13FlightTracker.java

@@ -0,0 +1,144 @@
+package org.bouncycastle.tls;
+
+import java.util.Enumeration;
+import java.util.Hashtable;
+import java.util.Vector;
+
+/**
+ * RFC 9147 7.2. Tracks which record carried which handshake fragment of the current outbound flight, so
+ * that an ACK retires exactly the fragments it covers and a retransmission resends only what is left.
+ * <p>
+ * A fragment may be registered more than once, under a different record number each time it is sent. It
+ * is acknowledged as soon as any one of those records is acknowledged.
+ * </p>
+ */
+class DTLS13FlightTracker
+{
+    /** One handshake fragment of the current outbound flight. */
+    static final class Fragment
+    {
+        private final int messageSeq;
+        private final int fragmentOffset;
+        private final int fragmentLength;
+
+        boolean acknowledged = false;
+
+        Fragment(int messageSeq, int fragmentOffset, int fragmentLength)
+        {
+            this.messageSeq = messageSeq;
+            this.fragmentOffset = fragmentOffset;
+            this.fragmentLength = fragmentLength;
+        }
+
+        int getMessageSeq()
+        {
+            return messageSeq;
+        }
+
+        int getFragmentOffset()
+        {
+            return fragmentOffset;
+        }
+
+        int getFragmentLength()
+        {
+            return fragmentLength;
+        }
+
+        private String key()
+        {
+            return messageSeq + ":" + fragmentOffset + ":" + fragmentLength;
+        }
+    }
+
+    // record number -> Fragment
+    private Hashtable carriers = new Hashtable();
+    // fragment key -> Fragment, so the same fragment sent twice is one entry
+    private Hashtable fragments = new Hashtable();
+    // fragments in registration order, for deterministic retransmission
+    private Vector order = new Vector();
+
+    void reset()
+    {
+        carriers = new Hashtable();
+        fragments = new Hashtable();
+        order = new Vector();
+    }
+
+    void register(DTLSRecordNumber recordNumber, int messageSeq, int fragmentOffset, int fragmentLength)
+    {
+        Fragment fragment = new Fragment(messageSeq, fragmentOffset, fragmentLength);
+        String key = fragment.key();
+
+        Fragment existing = (Fragment)fragments.get(key);
+        if (null == existing)
+        {
+            fragments.put(key, fragment);
+            order.addElement(fragment);
+            existing = fragment;
+        }
+
+        if (null != recordNumber)
+        {
+            carriers.put(recordNumber, existing);
+        }
+    }
+
+    void acknowledge(Vector recordNumbers)
+    {
+        for (int i = 0; i < recordNumbers.size(); ++i)
+        {
+            Fragment fragment = (Fragment)carriers.get(recordNumbers.elementAt(i));
+            if (null != fragment)
+            {
+                fragment.acknowledged = true;
+            }
+        }
+    }
+
+    boolean isEmpty()
+    {
+        return order.isEmpty();
+    }
+
+    /**
+     * @return true if fragments were registered and every one of them has been acknowledged.
+     */
+    boolean isComplete()
+    {
+        if (order.isEmpty())
+        {
+            return false;
+        }
+
+        Enumeration e = order.elements();
+        while (e.hasMoreElements())
+        {
+            if (!((Fragment)e.nextElement()).acknowledged)
+            {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    /**
+     * @return the fragments not yet acknowledged, in the order they were first registered.
+     */
+    Vector getOutstanding()
+    {
+        Vector outstanding = new Vector();
+
+        Enumeration e = order.elements();
+        while (e.hasMoreElements())
+        {
+            Fragment fragment = (Fragment)e.nextElement();
+            if (!fragment.acknowledged)
+            {
+                outstanding.addElement(fragment);
+            }
+        }
+
+        return outstanding;
+    }
+}

tls/src/main/java/org/bouncycastle/tls/DTLS13UnifiedHeader.java

@@ -0,0 +1,152 @@
+package org.bouncycastle.tls;
+
+/**
+ * RFC 9147 4. The DTLS 1.3 unified header for DTLSCiphertext records.
+ * <pre>
+ *  0 1 2 3 4 5 6 7
+ * +-+-+-+-+-+-+-+-+
+ * |0|0|1|C|S|L|E E|
+ * +-+-+-+-+-+-+-+-+
+ * </pre>
+ * C: connection ID present, S: 16-bit (1) or 8-bit (0) sequence number, L: length present, EE: low two bits of
+ * the epoch. Records written by this implementation always use the full form (S = 1, L = 1).
+ */
+class DTLS13UnifiedHeader
+{
+    static final int FIXED_BITS = 0x20;
+    static final int FIXED_BITS_MASK = 0xE0;
+    static final int FLAG_CID = 0x10;
+    static final int FLAG_SEQ16 = 0x08;
+    static final int FLAG_LENGTH = 0x04;
+    static final int EPOCH_BITS_MASK = 0x03;
+
+    /** RFC 9147 4.2.3. Record number encryption needs at least 16 bytes of ciphertext. */
+    static final int MIN_CIPHERTEXT_LENGTH = 16;
+
+    private static final long MAX_SEQUENCE_NUMBER = (1L << 48) - 1;
+
+    static boolean isCiphertextRecord(int firstByte)
+    {
+        return (firstByte & FIXED_BITS_MASK) == FIXED_BITS;
+    }
+
+    static boolean hasConnectionID(int firstByte)
+    {
+        return (firstByte & FLAG_CID) != 0;
+    }
+
+    static boolean hasSeq16(int firstByte)
+    {
+        return (firstByte & FLAG_SEQ16) != 0;
+    }
+
+    static boolean hasLength(int firstByte)
+    {
+        return (firstByte & FLAG_LENGTH) != 0;
+    }
+
+    static boolean matchesEpoch(int firstByte, int epoch)
+    {
+        return (firstByte & EPOCH_BITS_MASK) == (epoch & EPOCH_BITS_MASK);
+    }
+
+    static int getSequenceNumberLength(int firstByte)
+    {
+        return hasSeq16(firstByte) ? 2 : 1;
+    }
+
+    static int getHeaderLength(int firstByte, int connectionIDLength)
+    {
+        return 1 + connectionIDLength + getSequenceNumberLength(firstByte) + (hasLength(firstByte) ? 2 : 0);
+    }
+
+    static int getWriteHeaderLength(int connectionIDLength)
+    {
+        return 1 + connectionIDLength + 2 + 2;
+    }
+
+    /**
+     * The smallest conforming header a peer may send per RFC 9147 4: first byte, connection ID, and an 8-bit
+     * sequence number, with no length field (S = 0, L = 0). Since a peer is free to use that compact form,
+     * this is what the receive limit must budget for; assuming our own (full) write form would under-report the
+     * plaintext limit and reject legal records.
+     *
+     * @return the minimum length of a header that may be received.
+     */
+    static int getMinReadHeaderLength(int connectionIDLength)
+    {
+        return 1 + connectionIDLength + 1;
+    }
+
+    /**
+     * Write a full-form header (16-bit sequence number, length present). The length field is left zero for the
+     * cipher to fill in once the ciphertext length is known.
+     *
+     * @return the header length.
+     */
+    static int writeHeader(int epoch, long sequenceNumber, byte[] connectionID, byte[] buf, int off)
+    {
+        int cidLength = null == connectionID ? 0 : connectionID.length;
+
+        int firstByte = FIXED_BITS | FLAG_SEQ16 | FLAG_LENGTH | (epoch & EPOCH_BITS_MASK);
+        if (cidLength > 0)
+        {
+            firstByte |= FLAG_CID;
+        }
+
+        int pos = off;
+        buf[pos++] = (byte)firstByte;
+        if (cidLength > 0)
+        {
+            System.arraycopy(connectionID, 0, buf, pos, cidLength);
+            pos += cidLength;
+        }
+        TlsUtils.writeUint16((int)(sequenceNumber & 0xFFFFL), buf, pos);
+        pos += 2;
+        TlsUtils.writeUint16(0, buf, pos);
+        pos += 2;
+        return pos - off;
+    }
+
+    /**
+     * RFC 9147 4.2.2. Reconstruct the full sequence number as the value numerically closest to 'expected' (one
+     * plus the highest successfully deprotected sequence number) whose low 'seqBitCount' bits equal 'seqBits'.
+     */
+    static long reconstructSequenceNumber(long expected, int seqBits, int seqBitCount)
+    {
+        long modulus = 1L << seqBitCount;
+        long lowMask = modulus - 1;
+
+        long candidate = (expected & ~lowMask) | (seqBits & lowMask);
+        long best = candidate;
+        long bestDistance = distance(candidate, expected);
+
+        long lower = candidate - modulus;
+        if (lower >= 0)
+        {
+            long d = distance(lower, expected);
+            if (d < bestDistance)
+            {
+                best = lower;
+                bestDistance = d;
+            }
+        }
+
+        long upper = candidate + modulus;
+        if (upper <= MAX_SEQUENCE_NUMBER)
+        {
+            long d = distance(upper, expected);
+            if (d < bestDistance)
+            {
+                best = upper;
+            }
+        }
+
+        return best;
+    }
+
+    private static long distance(long a, long b)
+    {
+        return a > b ? a - b : b - a;
+    }
+}