From 6478a408e60162a0efa145d7647030b2b5ce9c83 Mon Sep 17 00:00:00 2001
From: Sun Yimin <emmansun@users.noreply.github.com>
Date: Tue, 8 Aug 2023 17:35:16 +0800
Subject: [PATCH] padding: ISO/IEC 9797 method 2

---
 padding/iso9797_m2.go      | 49 +++++++++++++++++++++++
 padding/iso9797_m2_test.go | 82 ++++++++++++++++++++++++++++++++++++++
 padding/schemes.go         |  7 ++++
 3 files changed, 138 insertions(+)
 create mode 100644 padding/iso9797_m2.go
 create mode 100644 padding/iso9797_m2_test.go

diff --git a/padding/iso9797_m2.go b/padding/iso9797_m2.go
new file mode 100644
index 0000000..64e776d
--- /dev/null
+++ b/padding/iso9797_m2.go
@@ -0,0 +1,49 @@
+package padding
+
+import (
+	"errors"
+
+	"github.com/emmansun/gmsm/internal/alias"
+)
+
+// Add a single bit with value 1 to the end of the data. 
+// Then if necessary add bits with value 0 to the end of the data until the padded data is a multiple of n.
+//
+// https://en.wikipedia.org/wiki/ISO/IEC_9797-1
+// also GB/T 17964-2021 C.2 Padding method 2
+type iso9797M2Padding uint
+
+func (pad iso9797M2Padding) BlockSize() int {
+	return int(pad)
+}
+
+func (pad iso9797M2Padding) Pad(src []byte) []byte {
+	overhead := pad.BlockSize() - len(src)%pad.BlockSize()
+	ret, out := alias.SliceForAppend(src, overhead)
+	out[0] = 0x80
+	for i := 1; i < overhead; i++ {
+		out[i] = 0
+	}
+	return ret
+}
+
+// Unpad decrypted plaintext, non-constant-time
+func (pad iso9797M2Padding) Unpad(src []byte) ([]byte, error) {
+	srcLen := len(src)
+	if srcLen == 0 || srcLen%pad.BlockSize() != 0 {
+		return nil, errors.New("iso/iec 9797-1 method 2: src length is not multiple of block size")
+	}
+	padStart := -1
+
+	for i, b := range src[srcLen-pad.BlockSize() : srcLen] {
+		if b == 0x80 {
+			padStart = i
+		} else if b != 0 && padStart >=0 {
+			padStart = -1
+		}
+	}
+	if padStart >= 0 {
+		return src[:srcLen-pad.BlockSize()+padStart], nil	
+	}
+	return src, nil
+}
diff --git a/padding/iso9797_m2_test.go b/padding/iso9797_m2_test.go
new file mode 100644
index 0000000..0f78f39
--- /dev/null
+++ b/padding/iso9797_m2_test.go
@@ -0,0 +1,82 @@
+package padding
+
+import (
+	"reflect"
+	"testing"
+)
+
+func Test_iso9797M2Padding_Pad(t *testing.T) {
+	iso9797 := NewISO9797M2Padding(16)
+	tests := []struct {
+		name string
+		src  []byte
+		want []byte
+	}{
+		{"16 bytes", []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15}, []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}},
+		{"15 bytes", []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}, []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 0x80}},
+		{"14 bytes", []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13}, []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 0x80, 0}},
+		{"13 bytes", []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12}, []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 0x80, 0, 0}},
+		{"12 bytes", []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11}, []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 0x80, 0, 0, 0}},
+		{"11 bytes", []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 0x80, 0, 0, 0, 0}},
+		{"10 bytes", []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}, []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0x80, 0, 0, 0, 0, 0}},
+		{"9 bytes", []byte{0, 1, 2, 3, 4, 5, 6, 7, 8}, []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 0x80, 0, 0, 0, 0, 0, 0}},
+		{"8 bytes", []byte{0, 1, 2, 3, 4, 5, 6, 7}, []byte{0, 1, 2, 3, 4, 5, 6, 7, 0x80, 0, 0, 0, 0, 0, 0, 0}},
+		{"7 bytes", []byte{0, 1, 2, 3, 4, 5, 6}, []byte{0, 1, 2, 3, 4, 5, 6, 0x80, 0, 0, 0, 0, 0, 0, 0, 0}},
+		{"6 bytes", []byte{0, 1, 2, 3, 4, 5}, []byte{0, 1, 2, 3, 4, 5, 0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0}},
+		{"5 bytes", []byte{0, 1, 2, 3, 4}, []byte{0, 1, 2, 3, 4, 0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}},
+		{"4 bytes", []byte{0, 1, 2, 3}, []byte{0, 1, 2, 3, 0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}},
+		{"3 bytes", []byte{0, 1, 2}, []byte{0, 1, 2, 0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}},
+		{"2 bytes", []byte{0, 1}, []byte{0, 1, 0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}},
+		{"1 bytes", []byte{0}, []byte{0, 0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := iso9797.Pad(tt.src); !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("iso9797M2Padding.Pad() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func Test_iso9797M2Padding_Unpad(t *testing.T) {
+	iso9797 := NewISO9797M2Padding(16)
+	tests := []struct {
+		name    string
+		want    []byte
+		src     []byte
+		wantErr bool
+	}{
+		{"16 bytes", []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15}, []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, false},
+		{"15 bytes", []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14}, []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 0x80}, false},
+		{"14 bytes", []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13}, []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 0x80, 0}, false},
+		{"13 bytes", []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12}, []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 0x80, 0, 0}, false},
+		{"12 bytes", []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11}, []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 0x80, 0, 0, 0}, false},
+		{"11 bytes", []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 0x80, 0, 0, 0, 0}, false},
+		{"10 bytes", []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}, []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0x80, 0, 0, 0, 0, 0}, false},
+		{"9 bytes", []byte{0, 1, 2, 3, 4, 5, 6, 7, 8}, []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 0x80, 0, 0, 0, 0, 0, 0}, false},
+		{"8 bytes", []byte{0, 1, 2, 3, 4, 5, 6, 7}, []byte{0, 1, 2, 3, 4, 5, 6, 7, 0x80, 0, 0, 0, 0, 0, 0, 0}, false},
+		{"7 bytes", []byte{0, 1, 2, 3, 4, 5, 6}, []byte{0, 1, 2, 3, 4, 5, 6, 0x80, 0, 0, 0, 0, 0, 0, 0, 0}, false},
+		{"6 bytes", []byte{0, 1, 2, 3, 4, 5}, []byte{0, 1, 2, 3, 4, 5, 0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0}, false},
+		{"5 bytes", []byte{0, 1, 2, 3, 4}, []byte{0, 1, 2, 3, 4, 0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, false},
+		{"4 bytes", []byte{0, 1, 2, 3}, []byte{0, 1, 2, 3, 0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, false},
+		{"3 bytes", []byte{0, 1, 2}, []byte{0, 1, 2, 0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, false},
+		{"2 bytes", []byte{0, 1}, []byte{0, 1, 0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, false},
+		{"1 bytes", []byte{0}, []byte{0, 0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, false},
+		{"1 bytes with tag", []byte{0x80}, []byte{0x80, 0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, false},
+		{"3 bytes with tag", []byte{0x80, 0, 0x80}, []byte{0x80, 0, 0x80, 0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, false},
+		{"19 bytes with tag", []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 0x80, 0, 0x80}, []byte{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 0x80, 0, 0x80, 0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, false},
+		{"invalid src length", nil, []byte{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, true},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := iso9797.Unpad(tt.src)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("case %v: iso9797M2Padding.Unpad() error = %v, wantErr %v", tt.name, err, tt.wantErr)
+				return
+			}
+			if !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("case %v: iso9797M2Padding.Unpad() = %v, want %v", tt.name, got, tt.want)
+			}
+		})
+	}
+}
diff --git a/padding/schemes.go b/padding/schemes.go
index 66c6273..e1f6c06 100644
--- a/padding/schemes.go
+++ b/padding/schemes.go
@@ -21,3 +21,10 @@ func NewANSIX923Padding(blockSize uint) Padding {
 	}
 	return ansiX923Padding(blockSize)
 }
+
+func NewISO9797M2Padding(blockSize uint) Padding {
+	if blockSize == 0 || blockSize > 255 {
+		panic("padding: invalid block size")
+	}
+	return iso9797M2Padding(blockSize)
+}