First Commit

analyzer/udp/internal/quic/payload.go

@@ -0,0 +1,122 @@
+package quic
+
+import (
+	"bytes"
+	"crypto"
+	"errors"
+	"fmt"
+	"io"
+	"sort"
+
+	"github.com/quic-go/quic-go/quicvarint"
+	"golang.org/x/crypto/hkdf"
+)
+
+func ReadCryptoPayload(packet []byte) ([]byte, error) {
+	hdr, offset, err := ParseInitialHeader(packet)
+	if err != nil {
+		return nil, err
+	}
+	// Some sanity checks
+	if hdr.Version != V1 && hdr.Version != V2 {
+		return nil, fmt.Errorf("unsupported version: %x", hdr.Version)
+	}
+	if offset == 0 || hdr.Length == 0 {
+		return nil, errors.New("invalid packet")
+	}
+
+	initialSecret := hkdf.Extract(crypto.SHA256.New, hdr.DestConnectionID, getSalt(hdr.Version))
+	clientSecret := hkdfExpandLabel(crypto.SHA256.New, initialSecret, "client in", []byte{}, crypto.SHA256.Size())
+	key, err := NewInitialProtectionKey(clientSecret, hdr.Version)
+	if err != nil {
+		return nil, fmt.Errorf("NewInitialProtectionKey: %w", err)
+	}
+	pp := NewPacketProtector(key)
+	// https://datatracker.ietf.org/doc/html/draft-ietf-quic-tls-32#name-client-initial
+	//
+	// "The unprotected header includes the connection ID and a 4-byte packet number encoding for a packet number of 2"
+	if int64(len(packet)) < offset+hdr.Length {
+		return nil, fmt.Errorf("packet is too short: %d < %d", len(packet), offset+hdr.Length)
+	}
+	unProtectedPayload, err := pp.UnProtect(packet[:offset+hdr.Length], offset, 2)
+	if err != nil {
+		return nil, err
+	}
+	frs, err := extractCryptoFrames(bytes.NewReader(unProtectedPayload))
+	if err != nil {
+		return nil, err
+	}
+	data := assembleCryptoFrames(frs)
+	if data == nil {
+		return nil, errors.New("unable to assemble crypto frames")
+	}
+	return data, nil
+}
+
+const (
+	paddingFrameType = 0x00
+	pingFrameType    = 0x01
+	cryptoFrameType  = 0x06
+)
+
+type cryptoFrame struct {
+	Offset int64
+	Data   []byte
+}
+
+func extractCryptoFrames(r *bytes.Reader) ([]cryptoFrame, error) {
+	var frames []cryptoFrame
+	for r.Len() > 0 {
+		typ, err := quicvarint.Read(r)
+		if err != nil {
+			return nil, err
+		}
+		if typ == paddingFrameType || typ == pingFrameType {
+			continue
+		}
+		if typ != cryptoFrameType {
+			return nil, fmt.Errorf("encountered unexpected frame type: %d", typ)
+		}
+		var frame cryptoFrame
+		offset, err := quicvarint.Read(r)
+		if err != nil {
+			return nil, err
+		}
+		frame.Offset = int64(offset)
+		dataLen, err := quicvarint.Read(r)
+		if err != nil {
+			return nil, err
+		}
+		frame.Data = make([]byte, dataLen)
+		if _, err := io.ReadFull(r, frame.Data); err != nil {
+			return nil, err
+		}
+		frames = append(frames, frame)
+	}
+	return frames, nil
+}
+
+// assembleCryptoFrames assembles multiple crypto frames into a single slice (if possible).
+// It returns an error if the frames cannot be assembled. This can happen if the frames are not contiguous.
+func assembleCryptoFrames(frames []cryptoFrame) []byte {
+	if len(frames) == 0 {
+		return nil
+	}
+	if len(frames) == 1 {
+		return frames[0].Data
+	}
+	// sort the frames by offset
+	sort.Slice(frames, func(i, j int) bool { return frames[i].Offset < frames[j].Offset })
+	// check if the frames are contiguous
+	for i := 1; i < len(frames); i++ {
+		if frames[i].Offset != frames[i-1].Offset+int64(len(frames[i-1].Data)) {
+			return nil
+		}
+	}
+	// concatenate the frames
+	data := make([]byte, frames[len(frames)-1].Offset+int64(len(frames[len(frames)-1].Data)))
+	for _, frame := range frames {
+		copy(data[frame.Offset:], frame.Data)
+	}
+	return data
+}