diff --git a/sm2/p256.go b/sm2/p256.go
index 923f46a..4c23655 100644
--- a/sm2/p256.go
+++ b/sm2/p256.go
@@ -10,6 +10,7 @@ import (
 )
 
 // See https://www.imperialviolet.org/2010/12/04/ecc.html ([1]) for background.
+// SM2 P256 parameters reference GB/T 32918.5-2017 part 5.
 
 type p256Curve struct {
 	*elliptic.CurveParams
diff --git a/sm2/sm2.go b/sm2/sm2.go
index 9a06087..864758f 100644
--- a/sm2/sm2.go
+++ b/sm2/sm2.go
@@ -5,6 +5,7 @@ package sm2
 //     http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.182.4503&rep=rep1&type=pdf
 //   [SECG]: SECG, SEC1
 //     http://www.secg.org/sec1-v2.pdf
+//   [GM/T]: SM2 GB/T 32918.2-2016, GB/T 32918.4-2016
 //
 
 import (
diff --git a/sm3/sm3.go b/sm3/sm3.go
index 3c1f136..4cd22b5 100644
--- a/sm3/sm3.go
+++ b/sm3/sm3.go
@@ -1,5 +1,7 @@
 package sm3
 
+// [GM/T] SM3 GB/T 32905-2016
+
 import (
 	"encoding/binary"
 	"errors"
diff --git a/sm4/block.go b/sm4/block.go
index 87df505..f8bd530 100644
--- a/sm4/block.go
+++ b/sm4/block.go
@@ -1,5 +1,7 @@
 package sm4
 
+// [GM/T] SM4 GB/T 32907-2016
+
 import (
 	"encoding/binary"
 	"math/bits"