diff --git a/CHANGELOG.md b/CHANGELOG.md
index 14d5cb4..866787a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -54,6 +54,7 @@ This document outlines major changes between releases.
 - Apply placement policies and copies if there is at least one valid value (#168)
 - Generalise config param `use_default_xmlns_for_complete_multipart` to `use_default_xmlns` so that use default xmlns for all requests (#221)
 - Set server IdleTimeout and ReadHeaderTimeout to `30s` and allow to configure them (#220)
+- Return `ETag` value in quotes (#219)
 
 ### Removed
 - Drop `tree.service` param (now endpoints from `peers` section are used) (#133)
diff --git a/api/data/info.go b/api/data/info.go
index b5c2a84..591de50 100644
--- a/api/data/info.go
+++ b/api/data/info.go
@@ -2,6 +2,7 @@ package data
 
 import (
 	"encoding/xml"
+	"strings"
 	"time"
 
 	cid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/container/id"
@@ -83,12 +84,12 @@ type (
 )
 
 // NotificationInfoFromObject creates new NotificationInfo from ObjectInfo.
-func NotificationInfoFromObject(objInfo *ObjectInfo) *NotificationInfo {
+func NotificationInfoFromObject(objInfo *ObjectInfo, md5Enabled bool) *NotificationInfo {
 	return &NotificationInfo{
 		Name:    objInfo.Name,
 		Version: objInfo.VersionID(),
 		Size:    objInfo.Size,
-		HashSum: objInfo.HashSum,
+		HashSum: Quote(objInfo.ETag(md5Enabled)),
 	}
 }
 
@@ -135,3 +136,11 @@ func (b BucketSettings) VersioningEnabled() bool {
 func (b BucketSettings) VersioningSuspended() bool {
 	return b.Versioning == VersioningSuspended
 }
+
+func Quote(val string) string {
+	return "\"" + val + "\""
+}
+
+func UnQuote(val string) string {
+	return strings.Trim(val, "\"")
+}
diff --git a/api/data/tree.go b/api/data/tree.go
index 2176690..5728eb3 100644
--- a/api/data/tree.go
+++ b/api/data/tree.go
@@ -93,9 +93,17 @@ type PartInfo struct {
 
 // ToHeaderString form short part representation to use in S3-Completed-Parts header.
 func (p *PartInfo) ToHeaderString() string {
+	// ETag value contains SHA256 checksum which is used while getting object parts attributes.
 	return strconv.Itoa(p.Number) + "-" + strconv.FormatUint(p.Size, 10) + "-" + p.ETag
 }
 
+func (p *PartInfo) GetETag(md5Enabled bool) string {
+	if md5Enabled && len(p.MD5) > 0 {
+		return p.MD5
+	}
+	return p.ETag
+}
+
 // LockInfo is lock information to create appropriate tree node.
 type LockInfo struct {
 	id uint64
diff --git a/api/handler/acl.go b/api/handler/acl.go
index 0472299..8ac6203 100644
--- a/api/handler/acl.go
+++ b/api/handler/acl.go
@@ -465,7 +465,7 @@ func (h *handler) PutObjectACLHandler(w http.ResponseWriter, r *http.Request) {
 	if updated {
 		s := &SendNotificationParams{
 			Event:            EventObjectACLPut,
-			NotificationInfo: data.NotificationInfoFromObject(objInfo),
+			NotificationInfo: data.NotificationInfoFromObject(objInfo, h.cfg.MD5Enabled()),
 			BktInfo:          bktInfo,
 			ReqInfo:          reqInfo,
 		}
@@ -642,7 +642,7 @@ func parseGrantee(grantees string) ([]*Grantee, error) {
 }
 
 func formGrantee(granteeType, value string) (*Grantee, error) {
-	value = strings.Trim(value, "\"")
+	value = data.UnQuote(value)
 	switch granteeType {
 	case "id":
 		return &Grantee{
diff --git a/api/handler/attributes.go b/api/handler/attributes.go
index 6cdbc29..c4e7880 100644
--- a/api/handler/attributes.go
+++ b/api/handler/attributes.go
@@ -1,6 +1,8 @@
 package handler
 
 import (
+	"encoding/base64"
+	"encoding/hex"
 	"fmt"
 	"net/http"
 	"strconv"
@@ -106,7 +108,7 @@ func (h *handler) GetObjectAttributesHandler(w http.ResponseWriter, r *http.Requ
 		return
 	}
 
-	if err = checkPreconditions(info, params.Conditional); err != nil {
+	if err = checkPreconditions(info, params.Conditional, h.cfg.MD5Enabled()); err != nil {
 		h.logAndSendError(w, "precondition failed", reqInfo, err)
 		return
 	}
@@ -117,7 +119,7 @@ func (h *handler) GetObjectAttributesHandler(w http.ResponseWriter, r *http.Requ
 		return
 	}
 
-	response, err := encodeToObjectAttributesResponse(info, params)
+	response, err := encodeToObjectAttributesResponse(info, params, h.cfg.MD5Enabled())
 	if err != nil {
 		h.logAndSendError(w, "couldn't encode object info to response", reqInfo, err)
 		return
@@ -179,19 +181,23 @@ func parseGetObjectAttributeArgs(r *http.Request) (*GetObjectAttributesArgs, err
 	return res, err
 }
 
-func encodeToObjectAttributesResponse(info *data.ObjectInfo, p *GetObjectAttributesArgs) (*GetObjectAttributesResponse, error) {
+func encodeToObjectAttributesResponse(info *data.ObjectInfo, p *GetObjectAttributesArgs, md5Enabled bool) (*GetObjectAttributesResponse, error) {
 	resp := &GetObjectAttributesResponse{}
 
 	for _, attr := range p.Attributes {
 		switch attr {
 		case eTag:
-			resp.ETag = info.HashSum
+			resp.ETag = data.Quote(info.ETag(md5Enabled))
 		case storageClass:
 			resp.StorageClass = api.DefaultStorageClass
 		case objectSize:
 			resp.ObjectSize = info.Size
 		case checksum:
-			resp.Checksum = &Checksum{ChecksumSHA256: info.HashSum}
+			checksumBytes, err := hex.DecodeString(info.HashSum)
+			if err != nil {
+				return nil, fmt.Errorf("form upload attributes: %w", err)
+			}
+			resp.Checksum = &Checksum{ChecksumSHA256: base64.StdEncoding.EncodeToString(checksumBytes)}
 		case objectParts:
 			parts, err := formUploadAttributes(info, p.MaxParts, p.PartNumberMarker)
 			if err != nil {
@@ -219,10 +225,15 @@ func formUploadAttributes(info *data.ObjectInfo, maxParts, marker int) (*ObjectP
 		if err != nil {
 			return nil, fmt.Errorf("invalid completed part: %w", err)
 		}
+		// ETag value contains SHA256 checksum.
+		checksumBytes, err := hex.DecodeString(part.ETag)
+		if err != nil {
+			return nil, fmt.Errorf("invalid sha256 checksum in completed part: %w", err)
+		}
 		parts[i] = Part{
 			PartNumber:     part.PartNumber,
 			Size:           int(part.Size),
-			ChecksumSHA256: part.ETag,
+			ChecksumSHA256: base64.StdEncoding.EncodeToString(checksumBytes),
 		}
 	}
 
diff --git a/api/handler/attributes_test.go b/api/handler/attributes_test.go
index 2889d73..0549d15 100644
--- a/api/handler/attributes_test.go
+++ b/api/handler/attributes_test.go
@@ -1,6 +1,8 @@
 package handler
 
 import (
+	"encoding/base64"
+	"encoding/hex"
 	"strings"
 	"testing"
 
@@ -24,11 +26,13 @@ func TestGetObjectPartsAttributes(t *testing.T) {
 	multipartUpload := createMultipartUpload(hc, bktName, objMultipartName, map[string]string{})
 	etag, _ := uploadPart(hc, bktName, objMultipartName, multipartUpload.UploadID, 1, partSize)
 	completeMultipartUpload(hc, bktName, objMultipartName, multipartUpload.UploadID, []string{etag})
+	etagBytes, err := hex.DecodeString(etag[1 : len(etag)-1])
+	require.NoError(t, err)
 
 	result = getObjectAttributes(hc, bktName, objMultipartName, objectParts)
 	require.NotNil(t, result.ObjectParts)
 	require.Len(t, result.ObjectParts.Parts, 1)
-	require.Equal(t, etag, result.ObjectParts.Parts[0].ChecksumSHA256)
+	require.Equal(t, base64.StdEncoding.EncodeToString(etagBytes), result.ObjectParts.Parts[0].ChecksumSHA256)
 	require.Equal(t, partSize, result.ObjectParts.Parts[0].Size)
 	require.Equal(t, 1, result.ObjectParts.PartsCount)
 }
diff --git a/api/handler/copy.go b/api/handler/copy.go
index 611d5f5..9f2dcdd 100644
--- a/api/handler/copy.go
+++ b/api/handler/copy.go
@@ -177,7 +177,7 @@ func (h *handler) CopyObjectHandler(w http.ResponseWriter, r *http.Request) {
 		}
 	}
 
-	if err = checkPreconditions(srcObjInfo, args.Conditional); err != nil {
+	if err = checkPreconditions(srcObjInfo, args.Conditional, h.cfg.MD5Enabled()); err != nil {
 		h.logAndSendError(w, "precondition failed", reqInfo, errors.GetAPIError(errors.ErrPreconditionFailed))
 		return
 	}
@@ -224,7 +224,10 @@ func (h *handler) CopyObjectHandler(w http.ResponseWriter, r *http.Request) {
 	}
 	dstObjInfo := extendedDstObjInfo.ObjectInfo
 
-	if err = middleware.EncodeToResponse(w, &CopyObjectResponse{LastModified: dstObjInfo.Created.UTC().Format(time.RFC3339), ETag: dstObjInfo.HashSum}); err != nil {
+	if err = middleware.EncodeToResponse(w, &CopyObjectResponse{
+		LastModified: dstObjInfo.Created.UTC().Format(time.RFC3339),
+		ETag:         data.Quote(dstObjInfo.ETag(h.cfg.MD5Enabled())),
+	}); err != nil {
 		h.logAndSendError(w, "something went wrong", reqInfo, err, additional...)
 		return
 	}
@@ -268,7 +271,7 @@ func (h *handler) CopyObjectHandler(w http.ResponseWriter, r *http.Request) {
 
 	s := &SendNotificationParams{
 		Event:            EventObjectCreatedCopy,
-		NotificationInfo: data.NotificationInfoFromObject(dstObjInfo),
+		NotificationInfo: data.NotificationInfoFromObject(dstObjInfo, h.cfg.MD5Enabled()),
 		BktInfo:          dstBktInfo,
 		ReqInfo:          reqInfo,
 	}
@@ -311,8 +314,8 @@ func isCopyingToItselfForbidden(reqInfo *middleware.ReqInfo, srcBucket string, s
 func parseCopyObjectArgs(headers http.Header) (*copyObjectArgs, error) {
 	var err error
 	args := &conditionalArgs{
-		IfMatch:     headers.Get(api.AmzCopyIfMatch),
-		IfNoneMatch: headers.Get(api.AmzCopyIfNoneMatch),
+		IfMatch:     data.UnQuote(headers.Get(api.AmzCopyIfMatch)),
+		IfNoneMatch: data.UnQuote(headers.Get(api.AmzCopyIfNoneMatch)),
 	}
 
 	if args.IfModifiedSince, err = parseHTTPTime(headers.Get(api.AmzCopyIfModifiedSince)); err != nil {
diff --git a/api/handler/get.go b/api/handler/get.go
index 7e27347..e5419e4 100644
--- a/api/handler/get.go
+++ b/api/handler/get.go
@@ -95,7 +95,7 @@ func writeHeaders(h http.Header, requestHeader http.Header, extendedInfo *data.E
 		h.Set(api.ContentLength, strconv.FormatUint(info.Size, 10))
 	}
 
-	h.Set(api.ETag, info.ETag(md5Enabled))
+	h.Set(api.ETag, data.Quote(info.ETag(md5Enabled)))
 
 	h.Set(api.AmzTaggingCount, strconv.Itoa(tagSetLength))
 	h.Set(api.AmzStorageClass, api.DefaultStorageClass)
@@ -157,7 +157,7 @@ func (h *handler) GetObjectHandler(w http.ResponseWriter, r *http.Request) {
 	}
 	info := extendedInfo.ObjectInfo
 
-	if err = checkPreconditions(info, conditional); err != nil {
+	if err = checkPreconditions(info, conditional, h.cfg.MD5Enabled()); err != nil {
 		h.logAndSendError(w, "precondition failed", reqInfo, err)
 		return
 	}
@@ -238,12 +238,13 @@ func (h *handler) GetObjectHandler(w http.ResponseWriter, r *http.Request) {
 	}
 }
 
-func checkPreconditions(info *data.ObjectInfo, args *conditionalArgs) error {
-	if len(args.IfMatch) > 0 && args.IfMatch != info.HashSum {
-		return fmt.Errorf("%w: etag mismatched: '%s', '%s'", errors.GetAPIError(errors.ErrPreconditionFailed), args.IfMatch, info.HashSum)
+func checkPreconditions(info *data.ObjectInfo, args *conditionalArgs, md5Enabled bool) error {
+	etag := info.ETag(md5Enabled)
+	if len(args.IfMatch) > 0 && args.IfMatch != etag {
+		return fmt.Errorf("%w: etag mismatched: '%s', '%s'", errors.GetAPIError(errors.ErrPreconditionFailed), args.IfMatch, etag)
 	}
-	if len(args.IfNoneMatch) > 0 && args.IfNoneMatch == info.HashSum {
-		return fmt.Errorf("%w: etag matched: '%s', '%s'", errors.GetAPIError(errors.ErrNotModified), args.IfNoneMatch, info.HashSum)
+	if len(args.IfNoneMatch) > 0 && args.IfNoneMatch == etag {
+		return fmt.Errorf("%w: etag matched: '%s', '%s'", errors.GetAPIError(errors.ErrNotModified), args.IfNoneMatch, etag)
 	}
 	if args.IfModifiedSince != nil && info.Created.Before(*args.IfModifiedSince) {
 		return fmt.Errorf("%w: not modified since '%s', last modified '%s'", errors.GetAPIError(errors.ErrNotModified),
@@ -267,8 +268,8 @@ func checkPreconditions(info *data.ObjectInfo, args *conditionalArgs) error {
 func parseConditionalHeaders(headers http.Header) (*conditionalArgs, error) {
 	var err error
 	args := &conditionalArgs{
-		IfMatch:     strings.Trim(headers.Get(api.IfMatch), "\""),
-		IfNoneMatch: strings.Trim(headers.Get(api.IfNoneMatch), "\""),
+		IfMatch:     data.UnQuote(headers.Get(api.IfMatch)),
+		IfNoneMatch: data.UnQuote(headers.Get(api.IfNoneMatch)),
 	}
 
 	if args.IfModifiedSince, err = parseHTTPTime(headers.Get(api.IfModifiedSince)); err != nil {
diff --git a/api/handler/get_test.go b/api/handler/get_test.go
index f6ce316..056694f 100644
--- a/api/handler/get_test.go
+++ b/api/handler/get_test.go
@@ -147,7 +147,7 @@ func TestPreconditions(t *testing.T) {
 		},
 	} {
 		t.Run(tc.name, func(t *testing.T) {
-			actual := checkPreconditions(tc.info, tc.args)
+			actual := checkPreconditions(tc.info, tc.args, false)
 			if tc.expected == nil {
 				require.NoError(t, actual)
 			} else {
@@ -203,11 +203,11 @@ func TestGetObjectEnabledMD5(t *testing.T) {
 	_, objInfo := createBucketAndObject(hc, bktName, objName)
 
 	_, headers := getObject(hc, bktName, objName)
-	require.Equal(t, objInfo.HashSum, headers.Get(api.ETag))
+	require.Equal(t, data.Quote(objInfo.HashSum), headers.Get(api.ETag))
 
 	hc.config.md5Enabled = true
 	_, headers = getObject(hc, bktName, objName)
-	require.Equal(t, objInfo.MD5Sum, headers.Get(api.ETag))
+	require.Equal(t, data.Quote(objInfo.MD5Sum), headers.Get(api.ETag))
 }
 
 func putObjectContent(hc *handlerContext, bktName, objName, content string) {
diff --git a/api/handler/head.go b/api/handler/head.go
index 272695c..93cc4e1 100644
--- a/api/handler/head.go
+++ b/api/handler/head.go
@@ -65,7 +65,7 @@ func (h *handler) HeadObjectHandler(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	if err = checkPreconditions(info, conditional); err != nil {
+	if err = checkPreconditions(info, conditional, h.cfg.MD5Enabled()); err != nil {
 		h.logAndSendError(w, "precondition failed", reqInfo, err)
 		return
 	}
diff --git a/api/handler/multipart_upload.go b/api/handler/multipart_upload.go
index 4f7fd0c..de095c9 100644
--- a/api/handler/multipart_upload.go
+++ b/api/handler/multipart_upload.go
@@ -264,7 +264,7 @@ func (h *handler) UploadPartHandler(w http.ResponseWriter, r *http.Request) {
 		addSSECHeaders(w.Header(), r.Header)
 	}
 
-	w.Header().Set(api.ETag, hash)
+	w.Header().Set(api.ETag, data.Quote(hash))
 	middleware.WriteSuccessResponseHeadersOnly(w)
 }
 
@@ -339,7 +339,7 @@ func (h *handler) UploadPartCopy(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	if err = checkPreconditions(srcInfo, args.Conditional); err != nil {
+	if err = checkPreconditions(srcInfo, args.Conditional, h.cfg.MD5Enabled()); err != nil {
 		h.logAndSendError(w, "precondition failed", reqInfo, errors.GetAPIError(errors.ErrPreconditionFailed),
 			additional...)
 		return
@@ -384,7 +384,7 @@ func (h *handler) UploadPartCopy(w http.ResponseWriter, r *http.Request) {
 
 	response := UploadPartCopyResponse{
 		LastModified: info.Created.UTC().Format(time.RFC3339),
-		ETag:         info.ETag(h.cfg.MD5Enabled()),
+		ETag:         data.Quote(info.ETag(h.cfg.MD5Enabled())),
 	}
 
 	if p.Info.Encryption.Enabled() {
@@ -449,7 +449,7 @@ func (h *handler) CompleteMultipartUploadHandler(w http.ResponseWriter, r *http.
 	response := CompleteMultipartUploadResponse{
 		Bucket: objInfo.Bucket,
 		Key:    objInfo.Name,
-		ETag:   objInfo.ETag(h.cfg.MD5Enabled()),
+		ETag:   data.Quote(objInfo.ETag(h.cfg.MD5Enabled())),
 	}
 
 	if settings.VersioningEnabled() {
@@ -513,7 +513,7 @@ func (h *handler) completeMultipartUpload(r *http.Request, c *layer.CompleteMult
 
 	s := &SendNotificationParams{
 		Event:            EventObjectCreatedCompleteMultipartUpload,
-		NotificationInfo: data.NotificationInfoFromObject(objInfo),
+		NotificationInfo: data.NotificationInfoFromObject(objInfo, h.cfg.MD5Enabled()),
 		BktInfo:          bktInfo,
 		ReqInfo:          reqInfo,
 	}
diff --git a/api/handler/multipart_upload_test.go b/api/handler/multipart_upload_test.go
index 0fcb6da..4e3d6d8 100644
--- a/api/handler/multipart_upload_test.go
+++ b/api/handler/multipart_upload_test.go
@@ -13,6 +13,7 @@ import (
 	"testing"
 
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api"
+	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/data"
 	s3Errors "git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/errors"
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer"
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer/encryption"
@@ -298,11 +299,11 @@ func TestMultipartUploadEnabledMD5(t *testing.T) {
 	multipartUpload := createMultipartUpload(hc, bktName, objName, map[string]string{})
 	etag1, partBody1 := uploadPart(hc, bktName, objName, multipartUpload.UploadID, 1, partSize)
 	md5Sum1 := md5.Sum(partBody1)
-	require.Equal(t, hex.EncodeToString(md5Sum1[:]), etag1)
+	require.Equal(t, data.Quote(hex.EncodeToString(md5Sum1[:])), etag1)
 
 	etag2, partBody2 := uploadPart(hc, bktName, objName, multipartUpload.UploadID, 2, partSize)
 	md5Sum2 := md5.Sum(partBody2)
-	require.Equal(t, hex.EncodeToString(md5Sum2[:]), etag2)
+	require.Equal(t, data.Quote(hex.EncodeToString(md5Sum2[:])), etag2)
 
 	w := completeMultipartUploadBase(hc, bktName, objName, multipartUpload.UploadID, []string{etag1, etag2})
 	assertStatus(t, w, http.StatusOK)
@@ -310,7 +311,7 @@ func TestMultipartUploadEnabledMD5(t *testing.T) {
 	err := xml.NewDecoder(w.Result().Body).Decode(resp)
 	require.NoError(t, err)
 	completeMD5Sum := md5.Sum(append(md5Sum1[:], md5Sum2[:]...))
-	require.Equal(t, hex.EncodeToString(completeMD5Sum[:])+"-2", resp.ETag)
+	require.Equal(t, data.Quote(hex.EncodeToString(completeMD5Sum[:])+"-2"), resp.ETag)
 }
 
 func uploadPartCopy(hc *handlerContext, bktName, objName, uploadID string, num int, srcObj string, start, end int) *UploadPartCopyResponse {
diff --git a/api/handler/object_list.go b/api/handler/object_list.go
index 88b2698..a8eb590 100644
--- a/api/handler/object_list.go
+++ b/api/handler/object_list.go
@@ -34,12 +34,12 @@ func (h *handler) ListObjectsV1Handler(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	if err = middleware.EncodeToResponse(w, encodeV1(params, list)); err != nil {
+	if err = middleware.EncodeToResponse(w, h.encodeV1(params, list)); err != nil {
 		h.logAndSendError(w, "something went wrong", reqInfo, err)
 	}
 }
 
-func encodeV1(p *layer.ListObjectsParamsV1, list *layer.ListObjectsInfoV1) *ListObjectsV1Response {
+func (h *handler) encodeV1(p *layer.ListObjectsParamsV1, list *layer.ListObjectsInfoV1) *ListObjectsV1Response {
 	res := &ListObjectsV1Response{
 		Name:         p.BktInfo.Name,
 		EncodingType: p.Encode,
@@ -53,7 +53,7 @@ func encodeV1(p *layer.ListObjectsParamsV1, list *layer.ListObjectsInfoV1) *List
 
 	res.CommonPrefixes = fillPrefixes(list.Prefixes, p.Encode)
 
-	res.Contents = fillContentsWithOwner(list.Objects, p.Encode)
+	res.Contents = fillContentsWithOwner(list.Objects, p.Encode, h.cfg.MD5Enabled())
 
 	return res
 }
@@ -78,12 +78,12 @@ func (h *handler) ListObjectsV2Handler(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	if err = middleware.EncodeToResponse(w, encodeV2(params, list)); err != nil {
+	if err = middleware.EncodeToResponse(w, h.encodeV2(params, list)); err != nil {
 		h.logAndSendError(w, "something went wrong", reqInfo, err)
 	}
 }
 
-func encodeV2(p *layer.ListObjectsParamsV2, list *layer.ListObjectsInfoV2) *ListObjectsV2Response {
+func (h *handler) encodeV2(p *layer.ListObjectsParamsV2, list *layer.ListObjectsInfoV2) *ListObjectsV2Response {
 	res := &ListObjectsV2Response{
 		Name:                  p.BktInfo.Name,
 		EncodingType:          p.Encode,
@@ -99,7 +99,7 @@ func encodeV2(p *layer.ListObjectsParamsV2, list *layer.ListObjectsInfoV2) *List
 
 	res.CommonPrefixes = fillPrefixes(list.Prefixes, p.Encode)
 
-	res.Contents = fillContents(list.Objects, p.Encode, p.FetchOwner)
+	res.Contents = fillContents(list.Objects, p.Encode, p.FetchOwner, h.cfg.MD5Enabled())
 
 	return res
 }
@@ -185,18 +185,18 @@ func fillPrefixes(src []string, encode string) []CommonPrefix {
 	return dst
 }
 
-func fillContentsWithOwner(src []*data.ObjectInfo, encode string) []Object {
-	return fillContents(src, encode, true)
+func fillContentsWithOwner(src []*data.ObjectInfo, encode string, md5Enabled bool) []Object {
+	return fillContents(src, encode, true, md5Enabled)
 }
 
-func fillContents(src []*data.ObjectInfo, encode string, fetchOwner bool) []Object {
+func fillContents(src []*data.ObjectInfo, encode string, fetchOwner, md5Enabled bool) []Object {
 	var dst []Object
 	for _, obj := range src {
 		res := Object{
 			Key:          s3PathEncode(obj.Name, encode),
 			Size:         obj.Size,
 			LastModified: obj.Created.UTC().Format(time.RFC3339),
-			ETag:         obj.HashSum,
+			ETag:         data.Quote(obj.ETag(md5Enabled)),
 			StorageClass: api.DefaultStorageClass,
 		}
 
@@ -292,7 +292,7 @@ func encodeListObjectVersionsToResponse(info *layer.ListObjectVersionsInfo, buck
 			},
 			Size:         ver.ObjectInfo.Size,
 			VersionID:    ver.Version(),
-			ETag:         ver.ObjectInfo.ETag(md5Enabled),
+			ETag:         data.Quote(ver.ObjectInfo.ETag(md5Enabled)),
 			StorageClass: api.DefaultStorageClass,
 		})
 	}
diff --git a/api/handler/put.go b/api/handler/put.go
index c69054c..4c923e9 100644
--- a/api/handler/put.go
+++ b/api/handler/put.go
@@ -276,7 +276,7 @@ func (h *handler) PutObjectHandler(w http.ResponseWriter, r *http.Request) {
 
 	s := &SendNotificationParams{
 		Event:            EventObjectCreatedPut,
-		NotificationInfo: data.NotificationInfoFromObject(objInfo),
+		NotificationInfo: data.NotificationInfoFromObject(objInfo, h.cfg.MD5Enabled()),
 		BktInfo:          bktInfo,
 		ReqInfo:          reqInfo,
 	}
@@ -327,7 +327,7 @@ func (h *handler) PutObjectHandler(w http.ResponseWriter, r *http.Request) {
 		addSSECHeaders(w.Header(), r.Header)
 	}
 
-	w.Header().Set(api.ETag, objInfo.ETag(h.cfg.MD5Enabled()))
+	w.Header().Set(api.ETag, data.Quote(objInfo.ETag(h.cfg.MD5Enabled())))
 
 	middleware.WriteSuccessResponseHeadersOnly(w)
 }
@@ -522,7 +522,7 @@ func (h *handler) PostObject(w http.ResponseWriter, r *http.Request) {
 
 	s := &SendNotificationParams{
 		Event:            EventObjectCreatedPost,
-		NotificationInfo: data.NotificationInfoFromObject(objInfo),
+		NotificationInfo: data.NotificationInfoFromObject(objInfo, h.cfg.MD5Enabled()),
 		BktInfo:          bktInfo,
 		ReqInfo:          reqInfo,
 	}
@@ -591,7 +591,7 @@ func (h *handler) PostObject(w http.ResponseWriter, r *http.Request) {
 			resp := &PostResponse{
 				Bucket: objInfo.Bucket,
 				Key:    objInfo.Name,
-				ETag:   objInfo.ETag(h.cfg.MD5Enabled()),
+				ETag:   data.Quote(objInfo.ETag(h.cfg.MD5Enabled())),
 			}
 			w.WriteHeader(status)
 			if _, err = w.Write(middleware.EncodeResponse(resp)); err != nil {
@@ -601,7 +601,7 @@ func (h *handler) PostObject(w http.ResponseWriter, r *http.Request) {
 		}
 	}
 
-	w.Header().Set(api.ETag, objInfo.HashSum)
+	w.Header().Set(api.ETag, data.Quote(objInfo.ETag(h.cfg.MD5Enabled())))
 	w.WriteHeader(status)
 }
 
diff --git a/api/handler/put_test.go b/api/handler/put_test.go
index 7ea41ae..0f360ac 100644
--- a/api/handler/put_test.go
+++ b/api/handler/put_test.go
@@ -19,6 +19,7 @@ import (
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api"
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/auth"
 	v4 "git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/auth/signer/v4"
+	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/data"
 	s3errors "git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/errors"
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/layer"
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/middleware"
@@ -204,7 +205,7 @@ func TestPutObjectWithEnabledMD5(t *testing.T) {
 	md5Hash.Write(content)
 	w, r := prepareTestPayloadRequest(tc, bktName, objName, bytes.NewReader(content))
 	tc.Handler().PutObjectHandler(w, r)
-	require.Equal(t, hex.EncodeToString(md5Hash.Sum(nil)), w.Header().Get(api.ETag))
+	require.Equal(t, data.Quote(hex.EncodeToString(md5Hash.Sum(nil))), w.Header().Get(api.ETag))
 }
 
 func TestPutObjectWithStreamBodyAWSExample(t *testing.T) {
diff --git a/api/layer/multipart_upload.go b/api/layer/multipart_upload.go
index 35e4b83..a6762c9 100644
--- a/api/layer/multipart_upload.go
+++ b/api/layer/multipart_upload.go
@@ -376,7 +376,7 @@ func (n *layer) CompleteMultipartUpload(ctx context.Context, p *CompleteMultipar
 	md5Hash := md5.New()
 	for i, part := range p.Parts {
 		partInfo := partsInfo[part.PartNumber]
-		if partInfo == nil || (part.ETag != partInfo.ETag && part.ETag != partInfo.MD5) {
+		if partInfo == nil || data.UnQuote(part.ETag) != partInfo.GetETag(n.features.MD5Enabled()) {
 			return nil, nil, fmt.Errorf("%w: unknown part %d or etag mismatched", s3errors.GetAPIError(s3errors.ErrInvalidPart), part.PartNumber)
 		}
 		delete(partsInfo, part.PartNumber)
@@ -571,7 +571,7 @@ func (n *layer) ListParts(ctx context.Context, p *ListPartsParams) (*ListPartsIn
 
 	for _, partInfo := range partsInfo {
 		parts = append(parts, &Part{
-			ETag:         partInfo.ETag,
+			ETag:         data.Quote(partInfo.GetETag(n.features.MD5Enabled())),
 			LastModified: partInfo.Created.UTC().Format(time.RFC3339),
 			PartNumber:   partInfo.Number,
 			Size:         partInfo.Size,
diff --git a/api/middleware/reqinfo.go b/api/middleware/reqinfo.go
index c857732..ad246ae 100644
--- a/api/middleware/reqinfo.go
+++ b/api/middleware/reqinfo.go
@@ -9,6 +9,7 @@ import (
 	"strings"
 	"sync"
 
+	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/api/data"
 	"git.frostfs.info/TrueCloudLab/frostfs-s3-gw/internal/logs"
 	"github.com/go-chi/chi/v5"
 	"github.com/google/uuid"
@@ -293,7 +294,7 @@ func getSourceIP(r *http.Request) string {
 		if match := forRegex.FindStringSubmatch(fwd); len(match) > 1 {
 			// IPv6 addresses in Forwarded headers are quoted-strings. We strip
 			// these quotes.
-			addr = strings.Trim(match[1], `"`)
+			addr = data.UnQuote(match[1])
 		}
 	}