feat: decrypt encrypted net-messages in CS2 demos (port of #696, #697)

Ports encrypted net-message support from v5 to v6:
- add svc_EncryptedData / CSVCMsg_EncryptedData and the related proto updates
- add ParserConfig.NetMessageDecryptionKey and MatchInfoDecryptionKey()
- decrypt and dispatch inner messages of CSVCMsg_EncryptedData
- extract msgCreatorForType() from handleDemoPacket() for reuse

Co-Authored-By: AkiVer <ys.renaud@gmail.com>
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: 3 people

go.mod

@@ -9,6 +9,7 @@ require (
 	github.com/markus-wa/go-unassert v0.1.3
 	github.com/markus-wa/gobitread v0.2.5
 	github.com/markus-wa/godispatch v1.4.1
+	github.com/markus-wa/ice-cipher-go v0.0.0-20230901094113-348096939ba7
 	github.com/markus-wa/quickhull-go/v2 v2.2.0
 	github.com/oklog/ulid/v2 v2.1.1
 	github.com/pkg/errors v0.9.1

go.sum

@@ -24,6 +24,8 @@ github.com/markus-wa/gobitread v0.2.5 h1:F5GxezkgQhnWsXWOf4mY1mLcSeDRI3onkIouG26
 github.com/markus-wa/gobitread v0.2.5/go.mod h1:PcWXMH4gx7o2CKslbkFkLyJB/aHW7JVRG3MRZe3PINg=
 github.com/markus-wa/godispatch v1.4.1 h1:Cdff5x33ShuX3sDmUbYWejk7tOuoHErFYMhUc2h7sLc=
 github.com/markus-wa/godispatch v1.4.1/go.mod h1:tk8L0yzLO4oAcFwM2sABMge0HRDJMdE8E7xm4gK/+xM=
+github.com/markus-wa/ice-cipher-go v0.0.0-20230901094113-348096939ba7 h1:aR9pvnlnBxifXBmzidpAiq2prLSGlkhE904qnk2sCz4=
+github.com/markus-wa/ice-cipher-go v0.0.0-20230901094113-348096939ba7/go.mod h1:JIsht5Oa9P50VnGJTvH2a6nkOqDFJbUeU1YRZYvdplw=
 github.com/markus-wa/quickhull-go/v2 v2.2.0 h1:rB99NLYeUHoZQ/aNRcGOGqjNBGmrOaRxdtqTnsTUPTA=
 github.com/markus-wa/quickhull-go/v2 v2.2.0/go.mod h1:EuLMucfr4B+62eipXm335hOs23LTnO62W7Psn3qvU2k=
 github.com/oklog/ulid/v2 v2.1.1 h1:suPZ4ARWLOJLegGFiZZ1dFAkqzhMjL3J1TzI+5wHz8s=

pkg/demoinfocs/events/events.go

@@ -645,6 +645,15 @@ const (
 	WarnTypeUserCommandBaselineMismatch
 
 	WarnTypeUnknownGrenadeModel // a grenade projectile's model hash isn't in the item->model map (e.g. a post-patch model variant)
+
+	// WarnTypeMissingNetMessageDecryptionKey occurs when encrypted net-messages are encountered and the decryption key is missing.
+	// See ParserConfig.NetMessageDecryptionKey
+	WarnTypeMissingNetMessageDecryptionKey
+
+	// WarnTypeCantReadEncryptedNetMessage occurs when an encrypted net-message can't be decrypted even though the decryption key is set.
+	// May occur because the decryption key used is incorrect.
+	// See ParserConfig.NetMessageDecryptionKey
+	WarnTypeCantReadEncryptedNetMessage
 )
 
 // WarnTypeUnknownDemoCommandMessageType occurs when a demo-command message type is unknown - contact a maintainer.

pkg/demoinfocs/matchinfo.go

@@ -0,0 +1,26 @@
+package demoinfocs
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/markus-wa/demoinfocs-golang/v6/pkg/demoinfocs/msg"
+	"github.com/pkg/errors"
+	"google.golang.org/protobuf/proto"
+)
+
+// MatchInfoDecryptionKey extracts the net-message decryption key stored in `match730_*.dem.info`.
+// Pass the whole contents of `match730_*.dem.info` to this function to get the key.
+// See also: ParserConfig.NetMessageDecryptionKey
+func MatchInfoDecryptionKey(b []byte) ([]byte, error) {
+	m := new(msg.CDataGCCStrike15V2_MatchInfo)
+
+	err := proto.Unmarshal(b, m)
+	if err != nil {
+		return nil, errors.Wrap(err, "failed to unmarshal MatchInfo message")
+	}
+
+	k := []byte(strings.ToUpper(fmt.Sprintf("%016x", m.GetWatchablematchinfo().GetClDecryptdataKeyPub())))
+
+	return k, nil
+}