diff --git a/drive.go b/drive.go
index f46f870..7a0758f 100644
--- a/drive.go
+++ b/drive.go
@@ -3,8 +3,10 @@ package proton_api_bridge
 import (
 	"context"
 	"log"
+	"runtime"
 
 	"github.com/henrybear327/Proton-API-Bridge/common"
+	"golang.org/x/sync/semaphore"
 
 	"github.com/ProtonMail/gopenpgp/v2/crypto"
 	"github.com/henrybear327/go-proton-api"
@@ -27,6 +29,8 @@ type ProtonDrive struct {
 	signatureAddress string
 
 	linkCache *linkCache
+
+	uploadEncryptionSem *semaphore.Weighted
 }
 
 func NewDefaultConfig() *common.Config {
@@ -144,6 +148,8 @@ func NewProtonDrive(ctx context.Context, config *common.Config, authHandler prot
 		signatureAddress: mainShare.Creator,
 
 		linkCache: newLinkCache(config.DisableLinkCaching),
+
+		uploadEncryptionSem: semaphore.NewWeighted(int64(runtime.GOMAXPROCS(0))),
 	}, credentials, nil
 }
 
diff --git a/file.go b/file.go
index 5e818b8..05fb6f4 100644
--- a/file.go
+++ b/file.go
@@ -7,9 +7,11 @@ import (
 	"crypto/sha256"
 	"encoding/base64"
 	"io"
+	"log"
 	"mime"
 	"os"
 	"path/filepath"
+	"sync"
 	"time"
 
 	"github.com/ProtonMail/gopenpgp/v2/crypto"
@@ -404,7 +406,58 @@ func (protonDrive *ProtonDrive) uploadAndCollectBlockData(ctx context.Context, n
 	}
 
 	shouldContinue := true
+	processData := func(blockIndex int, data []byte, wg *sync.WaitGroup, errorCh chan error) {
+		defer protonDrive.uploadEncryptionSem.Release(1)
+		defer wg.Done()
+
+		log.Println("processData start", linkID, blockIndex)
+		defer log.Println("processData done", linkID, blockIndex)
+
+		// encrypt data
+		dataPlainMessage := crypto.NewPlainMessage(data)
+		encData, err := newSessionKey.Encrypt(dataPlainMessage)
+		if err != nil {
+			errorCh <- err
+			return
+		}
+
+		encSignature, err := protonDrive.AddrKR.SignDetachedEncrypted(dataPlainMessage, newNodeKR)
+		if err != nil {
+			errorCh <- err
+			return
+		}
+		encSignatureStr, err := encSignature.GetArmored()
+		if err != nil {
+			errorCh <- err
+			return
+		}
+
+		h := sha256.New()
+		h.Write(encData)
+		hash := h.Sum(nil)
+		base64Hash := base64.StdEncoding.EncodeToString(hash)
+		if err != nil {
+			errorCh <- err
+			return
+		}
+		manifestSignatureData = append(manifestSignatureData, hash...)
+
+		pendingUploadBlocks = append(pendingUploadBlocks, PendingUploadBlocks{
+			blockUploadInfo: proton.BlockUploadInfo{
+				Index:        blockIndex, // iOS drive: BE starts with 1
+				Size:         int64(len(encData)),
+				EncSignature: encSignatureStr,
+				Hash:         base64Hash,
+			},
+			encData: encData,
+		})
+
+		errorCh <- nil
+	}
+	var wg sync.WaitGroup
+	errorCh := make(chan error, UPLOAD_BATCH_BLOCK_SIZE)
 	for i := 1; shouldContinue; i++ {
+		log.Println(linkID, i)
 		// read at most data of size UPLOAD_BLOCK_SIZE
 		data := make([]byte, UPLOAD_BLOCK_SIZE) // FIXME: get block size from the server config instead of hardcoding it
 		readBytes, err := file.Read(data)
@@ -424,46 +477,36 @@ func (protonDrive *ProtonDrive) uploadAndCollectBlockData(ctx context.Context, n
 		data = data[:readBytes]
 		totalFileSize += int64(readBytes)
 
-		// encrypt data
-		dataPlainMessage := crypto.NewPlainMessage(data)
-		encData, err := newSessionKey.Encrypt(dataPlainMessage)
+		if err := protonDrive.uploadEncryptionSem.Acquire(ctx, 1); err != nil {
+			return nil, 0, err
+		}
+		wg.Add(1)
+		go processData(i, data, &wg, errorCh)
 		if err != nil {
 			return nil, 0, err
 		}
 
-		encSignature, err := protonDrive.AddrKR.SignDetachedEncrypted(dataPlainMessage, newNodeKR)
-		if err != nil {
-			return nil, 0, err
-		}
-		encSignatureStr, err := encSignature.GetArmored()
-		if err != nil {
-			return nil, 0, err
-		}
-
-		h := sha256.New()
-		h.Write(encData)
-		hash := h.Sum(nil)
-		base64Hash := base64.StdEncoding.EncodeToString(hash)
-		if err != nil {
-			return nil, 0, err
-		}
-		manifestSignatureData = append(manifestSignatureData, hash...)
-
-		pendingUploadBlocks = append(pendingUploadBlocks, PendingUploadBlocks{
-			blockUploadInfo: proton.BlockUploadInfo{
-				Index:        i, // iOS drive: BE starts with 1
-				Size:         int64(len(encData)),
-				EncSignature: encSignatureStr,
-				Hash:         base64Hash,
-			},
-			encData: encData,
-		})
-
 		if (i-1) > 0 && (i-1)%UPLOAD_BATCH_BLOCK_SIZE == 0 {
+			wg.Wait()
+			close(errorCh)
+			for err := range errorCh {
+				if err != nil {
+					return nil, 0, err
+				}
+			}
 			err = uploadPendingBlocks()
 			if err != nil {
 				return nil, 0, err
 			}
+
+			errorCh = make(chan error, UPLOAD_BATCH_BLOCK_SIZE)
+		}
+	}
+	wg.Wait()
+	close(errorCh)
+	for err := range errorCh {
+		if err != nil {
+			return nil, 0, err
 		}
 	}
 	err := uploadPendingBlocks()