diff --git a/dev.sh b/dev.sh
index a116ef50..b8beda0c 100755
--- a/dev.sh
+++ b/dev.sh
@@ -11,7 +11,8 @@ export RM_SMTP_NOTLS=1
 export RM_SMTP_NOAUTH=1
 export JWT_SECRET_KEY=dev
 export LOGLEVEL=${1:-DEBUG}
-export STORAGE_URL=http://$(hostname):3000
+#export STORAGE_URL=http://$(hostname):3000
+#export STORAGE_URL=http://pc.lan:3000
 make runui &
 PID=$!
 trap "kill $PID ||:" EXIT 
diff --git a/go.mod b/go.mod
index c8c52b05..2a5a73d2 100644
--- a/go.mod
+++ b/go.mod
@@ -1,6 +1,6 @@
 module github.com/ddvk/rmfakecloud
 
-go 1.17
+go 1.23
 
 require (
 	github.com/dropbox/dropbox-sdk-go-unofficial/v6 v6.0.5
diff --git a/internal/app/handlers.go b/internal/app/handlers.go
index 738ce590..82b18558 100644
--- a/internal/app/handlers.go
+++ b/internal/app/handlers.go
@@ -743,7 +743,7 @@ func (app *App) syncUpdateRootV3(c *gin.Context) {
 	}
 
 	uid := c.GetString(userIDKey)
-	newgeneration, err := app.blobStorer.StoreBlob(uid, "root", bytes.NewBufferString(rootv3.Hash), rootv3.Generation)
+	newgeneration, err := app.blobStorer.StoreBlob(uid, RootHash, bytes.NewBufferString(rootv3.Hash), rootv3.Generation)
 	if err != nil {
 		log.Error(err)
 		c.AbortWithStatus(http.StatusInternalServerError)
@@ -759,24 +759,44 @@ func (app *App) syncUpdateRootV3(c *gin.Context) {
 	}
 
 	c.JSON(http.StatusOK, messages.SyncRootV3Response{
-		Generation:    newgeneration,
-		Hash:          rootv3.Hash,
-		SchemaVersion: SchemaVersion,
+		Generation: newgeneration,
+		Hash:       rootv3.Hash,
 	})
 }
 
 const SchemaVersion = 3
 
-func (app *App) syncGetRoot(c *gin.Context, newAccount func(*gin.Context)) {
-	uid := c.GetString(userIDKey)
+const RmTokenTtlHeader = "Rm-Token-Ttl-Hint"
+const RmFileHeader = "rm-filename"
+
+const RootHash = "root"
 
-	reader, generation, _, err := app.blobStorer.LoadBlob(uid, "root")
+// crcJSON calculates and ands the crc32c header
+// TODO: fix it with a custom render or something
+func crcJSON(c *gin.Context, status int, msg any) {
+	b, err := json.Marshal(msg)
+	if err != nil {
+		panic(err)
+	}
+
+	crc, err := common.CRC32FromReader(bytes.NewBuffer(b))
+	if err != nil {
+		panic(err)
+	}
+	common.AddCRCHeader(c, crc)
+	c.Data(status, "application/json", b)
+}
+
+func (app *App) syncGetRootV3(c *gin.Context) {
+	uid := c.GetString(userIDKey)
+	reader, generation, _, _, err := app.blobStorer.LoadBlob(uid, RootHash)
 	if err == fs.ErrorNotFound {
 		log.Warn("No root file found, assuming this is a new account")
-		newAccount(c)
 		c.JSON(http.StatusNotFound, gin.H{"message": "root not found"})
 		return
-	} else if err != nil {
+	}
+
+	if err != nil {
 		log.Error(err)
 		c.AbortWithStatus(http.StatusInternalServerError)
 		return
@@ -790,23 +810,38 @@ func (app *App) syncGetRoot(c *gin.Context, newAccount func(*gin.Context)) {
 	}
 
 	c.JSON(http.StatusOK, messages.SyncRootV3Response{
-		Generation:    generation,
-		Hash:          string(roothash),
-		SchemaVersion: SchemaVersion,
-	})
-}
-
-func (app *App) syncGetRootV3(c *gin.Context) {
-	app.syncGetRoot(c, func(c *gin.Context) {
-		c.JSON(http.StatusNotFound, gin.H{"message": "root not found"})
+		Generation: generation,
+		Hash:       string(roothash),
 	})
 }
 
 func (app *App) syncGetRootV4(c *gin.Context) {
-	app.syncGetRoot(c, func(c *gin.Context) {
-		c.JSON(http.StatusOK, messages.SyncRootV3Response{
-			Generation: 0,
+	uid := c.GetString(userIDKey)
+	reader, generation, _, _, err := app.blobStorer.LoadBlob(uid, RootHash)
+	if err == fs.ErrorNotFound {
+		log.Warn("No root file found, assuming this is a new account")
+		crcJSON(c, http.StatusOK, messages.SyncRootV4Response{
+			SchemaVersion: SchemaVersion,
 		})
+		return
+	}
+
+	if err != nil {
+		log.Error(err)
+		c.AbortWithStatus(http.StatusInternalServerError)
+		return
+	}
+
+	roothash, err := io.ReadAll(reader)
+	if err != nil {
+		log.Error(err)
+		c.AbortWithStatus(http.StatusInternalServerError)
+		return
+	}
+	crcJSON(c, http.StatusOK, messages.SyncRootV4Response{
+		Generation:    generation,
+		Hash:          string(roothash),
+		SchemaVersion: SchemaVersion,
 	})
 }
 
@@ -843,13 +878,14 @@ func (app *App) blobStorageRead(c *gin.Context) {
 	uid := c.GetString(userIDKey)
 	blobID := common.ParamS(fileKey, c)
 
-	reader, _, size, err := app.blobStorer.LoadBlob(uid, blobID)
+	reader, _, size, crc32c, err := app.blobStorer.LoadBlob(uid, blobID)
 	if err != nil {
 		log.Error(err)
 		c.AbortWithStatus(http.StatusInternalServerError)
 		return
 	}
 	defer reader.Close()
+	common.AddCRCHeader(c, crc32c)
 
 	c.DataFromReader(http.StatusOK, size, "application/octet-stream", reader, nil)
 }
@@ -858,6 +894,10 @@ func (app *App) blobStorageWrite(c *gin.Context) {
 	uid := c.GetString(userIDKey)
 	blobID := common.ParamS(fileKey, c)
 
+	fileName := c.GetHeader(RmFileHeader)
+	hash := c.GetHeader(common.CRC32CHashHeader)
+	log.Debugf("TODO: check/save etc. write file '%s', hash '%s'", fileName, hash)
+
 	newgeneration, err := app.blobStorer.StoreBlob(uid, blobID, c.Request.Body, 0)
 	if err != nil {
 		log.Error(err)
@@ -865,7 +905,8 @@ func (app *App) blobStorageWrite(c *gin.Context) {
 		return
 	}
 
-	c.JSON(http.StatusOK, messages.SyncRootV3Response{
+	//not checked by the client yet, but who knows
+	crcJSON(c, http.StatusOK, messages.SyncRootV4Response{
 		Generation:    newgeneration,
 		Hash:          string(blobID),
 		SchemaVersion: SchemaVersion,
@@ -1040,6 +1081,27 @@ func (app *App) connectWebSocket(c *gin.Context) {
 	go app.hub.ConnectWs(uid, deviceID, connection)
 }
 
+// syncReports reports sync errors back
+func (app *App) syncReports(c *gin.Context) {
+	body, err := io.ReadAll(c.Request.Body)
+
+	if err != nil {
+		log.Warn("cant parse sync report, ignored")
+		c.Status(http.StatusOK)
+		return
+	}
+	log.Infof("got sync report: %s", string(body))
+	c.Status(http.StatusOK)
+}
+
+func (app *App) nullReport(c *gin.Context) {
+	_, err := io.ReadAll(c.Request.Body)
+	if err != nil {
+		log.Warn("could not read report data")
+	}
+	c.Status(http.StatusOK)
+}
+
 // / remove remarkable ads
 func stripAds(msg string) string {
 	br := "<br>--<br>"
diff --git a/internal/app/routes.go b/internal/app/routes.go
index 703a56d8..4601251d 100644
--- a/internal/app/routes.go
+++ b/internal/app/routes.go
@@ -41,6 +41,7 @@ func (app *App) registerRoutes(router *gin.Engine) {
 			c.AbortWithStatusJSON(http.StatusInternalServerError, gin.H{"err": err.Error()})
 			return
 		}
+		log.Infof("endpoint %s", endpoint)
 		c.JSON(http.StatusOK, gin.H{
 			"Status": "OK",
 			"Host":   endpoint,
@@ -80,27 +81,11 @@ func (app *App) registerRoutes(router *gin.Engine) {
 		c.Status(http.StatusOK)
 	})
 
+	router.POST("/analytics/v2/events", app.nullReport)
 	//some telemetry stuff from ping.
-	router.POST("/v1/reports", func(c *gin.Context) {
-		_, err := io.ReadAll(c.Request.Body)
-
-		if err != nil {
-			log.Warn("cant parse telemetry, ignored")
-			c.Status(http.StatusOK)
-			return
-		}
-		c.Status(http.StatusOK)
-	})
-	router.POST("/v2/reports", func(c *gin.Context) {
-		_, err := io.ReadAll(c.Request.Body)
-
-		if err != nil {
-			log.Warn("cant parse telemetry, ignored")
-			c.Status(http.StatusOK)
-			return
-		}
-		c.Status(http.StatusOK)
-	})
+	router.POST("/v1/reports", app.nullReport)
+	router.POST("/v2/reports", app.nullReport)
+	router.POST("/report/v1", app.nullReport)
 
 	//routes needing api authentitcation
 	authRoutes := router.Group("/")
@@ -159,5 +144,8 @@ func (app *App) registerRoutes(router *gin.Engine) {
 		authRoutes.GET("/sync/v3/missing", app.checkMissingBlob)
 
 		authRoutes.GET("/sync/v4/root", app.syncGetRootV4)
+
+		// reports
+		authRoutes.POST("/sync/reports/v1", app.syncReports)
 	}
 }
diff --git a/internal/common/common.go b/internal/common/common.go
index 2e1b1251..3be999ad 100644
--- a/internal/common/common.go
+++ b/internal/common/common.go
@@ -1,7 +1,11 @@
 package common
 
 import (
+	"encoding/base64"
+	"encoding/binary"
 	"errors"
+	"hash/crc32"
+	"io"
 	"regexp"
 	"strings"
 
@@ -62,3 +66,32 @@ func ParamS(param string, c *gin.Context) string {
 	p := c.Param(param)
 	return Sanitize(p)
 }
+
+var table = crc32.MakeTable(crc32.Castagnoli)
+
+func CRC32FromReader(reader io.Reader) (string, error) {
+	// Create a table for CRC32C (Castagnoli polynomial)
+	// Create a CRC32C hasher
+	crc32c := crc32.New(table)
+
+	// Copy the reader data into the hasher
+	if _, err := io.Copy(crc32c, reader); err != nil {
+		return "", err
+	}
+
+	// Compute the CRC32C checksum
+	checksum := crc32c.Sum32()
+
+	// Convert the checksum to a byte array
+	crcBytes := make([]byte, 4)
+	binary.BigEndian.PutUint32(crcBytes, checksum)
+	encodedChecksum := base64.StdEncoding.EncodeToString(crcBytes)
+
+	return encodedChecksum, nil
+}
+
+const CRC32CHashHeader = "x-goog-hash"
+
+func AddCRCHeader(c *gin.Context, crc string) {
+	c.Header(CRC32CHashHeader, "crc32c="+crc)
+}
diff --git a/internal/messages/messages.go b/internal/messages/messages.go
index efab3192..4d4ac03c 100644
--- a/internal/messages/messages.go
+++ b/internal/messages/messages.go
@@ -145,6 +145,12 @@ type SyncRootV3Request struct {
 
 // SyncRootV3Response
 type SyncRootV3Response struct {
+	Generation int64  `json:"generation"`
+	Hash       string `json:"hash,omitempty"`
+}
+
+// SyncRootV4Response
+type SyncRootV4Response struct {
 	Generation    int64  `json:"generation"`
 	Hash          string `json:"hash,omitempty"`
 	SchemaVersion int64  `json:"schemaVersion"`
diff --git a/internal/storage/fs/app.go b/internal/storage/fs/app.go
index bb717315..f0e4cd38 100644
--- a/internal/storage/fs/app.go
+++ b/internal/storage/fs/app.go
@@ -151,7 +151,7 @@ func (app *App) downloadBlob(c *gin.Context) {
 
 	log.Info("Requestng blob: ", blobID)
 
-	reader, generation, size, err := app.fs.LoadBlob(uid, blobID)
+	reader, generation, size, crc32c, err := app.fs.LoadBlob(uid, blobID)
 	if err != nil {
 		if err == ErrorNotFound {
 			c.AbortWithStatus(http.StatusNotFound)
@@ -163,6 +163,8 @@ func (app *App) downloadBlob(c *gin.Context) {
 	}
 	defer reader.Close()
 
+	common.AddCRCHeader(c, crc32c)
+
 	if blobID == rootBlob {
 		log.Debug("Sending gen for root: ", generation)
 		c.Header(generationHeader, strconv.FormatInt(generation, 10))
diff --git a/internal/storage/fs/blobstore.go b/internal/storage/fs/blobstore.go
index 6f714b39..b05fceca 100644
--- a/internal/storage/fs/blobstore.go
+++ b/internal/storage/fs/blobstore.go
@@ -454,7 +454,7 @@ func (fs *FileSystemStorage) GetBlobURL(uid, blobid string, write bool) (docurl
 }
 
 // LoadBlob Opens a blob by id
-func (fs *FileSystemStorage) LoadBlob(uid, blobid string) (reader io.ReadCloser, gen int64, size int64, err error) {
+func (fs *FileSystemStorage) LoadBlob(uid, blobid string) (reader io.ReadCloser, gen int64, size int64, crc32 string, err error) {
 	generation := int64(0)
 	blobPath := path.Join(fs.getUserBlobPath(uid), common.Sanitize(blobid))
 	log.Debugln("Fullpath:", blobPath)
@@ -464,7 +464,7 @@ func (fs *FileSystemStorage) LoadBlob(uid, blobid string) (reader io.ReadCloser,
 		err := lock.LockWithTimeout(time.Duration(time.Second * 5))
 		if err != nil {
 			log.Error("cannot obtain lock")
-			return nil, 0, 0, err
+			return nil, 0, 0, "", err
 		}
 		defer lock.Unlock()
 
@@ -476,11 +476,23 @@ func (fs *FileSystemStorage) LoadBlob(uid, blobid string) (reader io.ReadCloser,
 
 	fi, err := os.Stat(blobPath)
 	if err != nil || fi.IsDir() {
-		return nil, generation, 0, ErrorNotFound
+		return nil, generation, 0, "", ErrorNotFound
 	}
 
-	reader, err = os.Open(blobPath)
-	return reader, generation, fi.Size(), err
+	osFile, err := os.Open(blobPath)
+	//TODO: cache the crc32
+	crc32, err = common.CRC32FromReader(osFile)
+	if err != nil {
+		log.Errorf("cannot get crc32 hash %v", err)
+		return
+	}
+	_, err = osFile.Seek(0, 0)
+	if err != nil {
+		log.Errorf("cannot rewind file %v", err)
+		return
+	}
+	reader = osFile
+	return reader, generation, fi.Size(), crc32, err
 }
 
 // StoreBlob stores a document
diff --git a/internal/storage/fs/localblobstorage.go b/internal/storage/fs/localblobstorage.go
index ae072869..02fcc46d 100644
--- a/internal/storage/fs/localblobstorage.go
+++ b/internal/storage/fs/localblobstorage.go
@@ -15,7 +15,7 @@ type LocalBlobStorage struct {
 
 // GetRootIndex the hash of the root index
 func (p *LocalBlobStorage) GetRootIndex() (hash string, gen int64, err error) {
-	r, gen, _, err := p.fs.LoadBlob(p.uid, rootBlob)
+	r, gen, _, _, err := p.fs.LoadBlob(p.uid, rootBlob)
 	if err == ErrorNotFound {
 		log.Info("root not found")
 		return "", gen, nil
@@ -40,7 +40,7 @@ func (p *LocalBlobStorage) WriteRootIndex(generation int64, roothash string) (in
 
 // GetReader reader for a given hash
 func (p *LocalBlobStorage) GetReader(hash string) (io.ReadCloser, error) {
-	r, _, _, err := p.fs.LoadBlob(p.uid, hash)
+	r, _, _, _, err := p.fs.LoadBlob(p.uid, hash)
 	return r, err
 }
 
diff --git a/internal/storage/storage.go b/internal/storage/storage.go
index 2ee9d778..21f29dd7 100644
--- a/internal/storage/storage.go
+++ b/internal/storage/storage.go
@@ -34,7 +34,7 @@ type BlobStorage interface {
 	GetBlobURL(uid, docid string, write bool) (string, time.Time, error)
 
 	StoreBlob(uid, blobID string, s io.Reader, matchGeneration int64) (int64, error)
-	LoadBlob(uid, blobID string) (reader io.ReadCloser, gen int64, size int64, err error)
+	LoadBlob(uid, blobID string) (reader io.ReadCloser, gen int64, size int64, crc32c string, err error)
 	CreateBlobDocument(uid, name, parent string, stream io.Reader) (doc *Document, err error)
 }