diff --git a/service/sign.go b/service/sign.go
index 50453b9..796a4cd 100644
--- a/service/sign.go
+++ b/service/sign.go
@@ -137,11 +137,24 @@ func verifySignatures(src SignedDataSource, items ...SignKeyPair) error {
 	}
 	defer bytesPool.Put(data)
 
-	for _, signKey := range items {
+	for i := range items {
+		if i > 0 {
+			// add previous key bytes to the signed message
+
+			signKeyDataSrc := SignKeyPairsSignedData(items[i-1])
+
+			signKeyData, err := signKeyDataSrc.SignedData()
+			if err != nil {
+				return errors.Wrapf(err, "could not get signed data of key-signature #%d", i)
+			}
+
+			data = append(data, signKeyData...)
+		}
+
 		if err := crypto.Verify(
-			signKey.GetPublicKey(),
+			items[i].GetPublicKey(),
 			data,
-			signKey.GetSignature(),
+			items[i].GetSignature(),
 		); err != nil {
 			return err
 		}
@@ -213,6 +226,7 @@ func SignRequestData(key *ecdsa.PrivateKey, src RequestSignedData) error {
 			src.GetBearerToken(),
 		),
 		ExtendedHeadersSignedData(src),
+		SignKeyPairsSignedData(src.GetSignKeyPairs()...),
 	)
 	if err != nil {
 		return err
diff --git a/service/sign_test.go b/service/sign_test.go
index 6f1e913..3c54e8c 100644
--- a/service/sign_test.go
+++ b/service/sign_test.go
@@ -15,13 +15,13 @@ import (
 type testSignedDataSrc struct {
 	err   error
 	data  []byte
-	sig   []byte
-	key   *ecdsa.PublicKey
 	token SessionToken
 
 	bearer BearerToken
 
 	extHdrs []ExtendedHeader
+
+	signKeys []SignKeyPair
 }
 
 type testSignedDataReader struct {
@@ -29,13 +29,15 @@ type testSignedDataReader struct {
 }
 
 func (s testSignedDataSrc) GetSignature() []byte {
-	return s.sig
+	if len(s.signKeys) > 0 {
+		return s.signKeys[0].GetSignature()
+	}
+
+	return nil
 }
 
 func (s testSignedDataSrc) GetSignKeyPairs() []SignKeyPair {
-	return []SignKeyPair{
-		newSignatureKeyPair(s.key, s.sig),
-	}
+	return s.signKeys
 }
 
 func (s testSignedDataSrc) SignedData() ([]byte, error) {
@@ -43,8 +45,9 @@ func (s testSignedDataSrc) SignedData() ([]byte, error) {
 }
 
 func (s *testSignedDataSrc) AddSignKey(sig []byte, key *ecdsa.PublicKey) {
-	s.key = key
-	s.sig = sig
+	s.signKeys = append(s.signKeys,
+		newSignatureKeyPair(key, sig),
+	)
 }
 
 func testData(t *testing.T, sz int) []byte {
@@ -209,23 +212,27 @@ func TestVerifyAccumulatedSignatures(t *testing.T) {
 	// create test private key
 	sk := test.DecodeKey(0)
 
+	signKey := new(RequestVerificationHeader_Signature)
+	signKey.Peer = crypto.MarshalPublicKey(&sk.PublicKey)
+
 	// create signature source
 	src := &testSignedDataSrc{
 		data: testData(t, 10),
-		key:  &sk.PublicKey,
+
+		signKeys: []SignKeyPair{signKey},
 	}
 
 	var err error
 
 	// calculate a signature
-	src.sig, err = crypto.Sign(sk, src.data)
+	signKey.Sign, err = crypto.Sign(sk, src.data)
 	require.NoError(t, err)
 
 	// ascertain that verification is passed
 	require.NoError(t, VerifyAccumulatedSignatures(src))
 
 	// break the signature
-	src.sig[0]++
+	signKey.Sign[0]++
 
 	// ascertain that verification is failed
 	require.Error(t, VerifyAccumulatedSignatures(src))
@@ -238,9 +245,13 @@ func TestVerifySignatureWithKey(t *testing.T) {
 		ErrEmptyDataWithSignature.Error(),
 	)
 
+	signKey := new(RequestVerificationHeader_Signature)
+
 	// create test signature source
 	src := &testSignedDataSrc{
 		data: testData(t, 10),
+
+		signKeys: []SignKeyPair{signKey},
 	}
 
 	// nil public key
@@ -255,14 +266,14 @@ func TestVerifySignatureWithKey(t *testing.T) {
 	var err error
 
 	// calculate a signature
-	src.sig, err = crypto.Sign(sk, src.data)
+	signKey.Sign, err = crypto.Sign(sk, src.data)
 	require.NoError(t, err)
 
 	// ascertain that verification is passed
 	require.NoError(t, VerifySignatureWithKey(&sk.PublicKey, src))
 
 	// break the signature
-	src.sig[0]++
+	signKey.Sign[0]++
 
 	// ascertain that verification is failed
 	require.Error(t, VerifySignatureWithKey(&sk.PublicKey, src))
@@ -375,4 +386,15 @@ func TestSignVerifyRequestData(t *testing.T) {
 
 	// ascertain that verification is passed
 	require.NoError(t, VerifyRequestData(rdr))
+
+	if len(rdr.GetSignKeyPairs()) < 2 {
+		// add one more signature
+		require.NoError(t, SignRequestData(test.DecodeKey(1), rdr))
+	}
+
+	// change key-signature order
+	rdr.signKeys[0], rdr.signKeys[1] = rdr.signKeys[1], rdr.signKeys[0]
+
+	// ascertain that verification is failed
+	require.Error(t, VerifyRequestData(src))
 }
diff --git a/service/types.go b/service/types.go
index 75a5a0a..785a30a 100644
--- a/service/types.go
+++ b/service/types.go
@@ -262,6 +262,7 @@ type RequestData interface {
 type RequestSignedData interface {
 	RequestData
 	SignKeyPairAccumulator
+	SignKeyPairSource
 }
 
 // RequestVerifyData is an interface of request information with signature read access.
diff --git a/service/verify.go b/service/verify.go
index e1caa06..7691220 100644
--- a/service/verify.go
+++ b/service/verify.go
@@ -2,11 +2,16 @@ package service
 
 import (
 	"crypto/ecdsa"
+	"io"
 
 	"github.com/nspcc-dev/neofs-api-go/internal"
 	crypto "github.com/nspcc-dev/neofs-crypto"
 )
 
+type signKeyPairsWrapper struct {
+	items []SignKeyPair
+}
+
 // GetSessionToken returns SessionToken interface of Token field.
 //
 // If token field value is nil, nil returns.
@@ -114,3 +119,48 @@ func (m RequestVerificationHeader) GetBearerToken() BearerToken {
 
 	return nil
 }
+
+// SignKeyPairsSignedData wraps passed SignKeyPair slice and returns SignedDataSource interface.
+func SignKeyPairsSignedData(v ...SignKeyPair) SignedDataSource {
+	return &signKeyPairsWrapper{
+		items: v,
+	}
+}
+
+// SignedData returns signed SignKeyPair slice in a binary representation.
+func (s signKeyPairsWrapper) SignedData() ([]byte, error) {
+	return SignedDataFromReader(s)
+}
+
+// SignedDataSize returns the length of signed SignKeyPair slice.
+func (s signKeyPairsWrapper) SignedDataSize() (sz int) {
+	for i := range s.items {
+		// add key length
+		sz += len(
+			crypto.MarshalPublicKey(s.items[i].GetPublicKey()),
+		)
+	}
+
+	return
+}
+
+// ReadSignedData copies a binary representation of the signed SignKeyPair slice to passed buffer.
+//
+// If buffer length is less than required, io.ErrUnexpectedEOF returns.
+func (s signKeyPairsWrapper) ReadSignedData(p []byte) (int, error) {
+	sz := s.SignedDataSize()
+	if len(p) < sz {
+		return 0, io.ErrUnexpectedEOF
+	}
+
+	off := 0
+
+	for i := range s.items {
+		// copy public key bytes
+		off += copy(p[off:], crypto.MarshalPublicKey(
+			s.items[i].GetPublicKey(),
+		))
+	}
+
+	return off, nil
+}