From 0781c12ede58390a77f6ea5c7245e120895a6127 Mon Sep 17 00:00:00 2001
From: Ethan Frey <ethanfrey@users.noreply.github.com>
Date: Fri, 28 Jul 2017 23:44:16 -0400
Subject: [PATCH] Message encoding for nano

---
 nano/sign.go      | 59 +++++++++++++++++++++++++++++++++++++++++++++++
 nano/sign_test.go | 51 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 110 insertions(+)
 create mode 100644 nano/sign.go
 create mode 100644 nano/sign_test.go

diff --git a/nano/sign.go b/nano/sign.go
new file mode 100644
index 000000000..fbe550548
--- /dev/null
+++ b/nano/sign.go
@@ -0,0 +1,59 @@
+package nano
+
+import (
+	"bytes"
+	"fmt"
+
+	"github.com/pkg/errors"
+)
+
+const (
+	App       = 0x80
+	Init      = 0x00
+	Update    = 0x01
+	Digest    = 0x02
+	MaxChunk  = 253
+	KeyLength = 65
+	SigLength = 64
+)
+
+var separator = []byte{0, 0xCA, 0xFE, 0}
+
+func generateSignRequests(payload []byte) [][]byte {
+	// nice one-shot
+	digest := []byte{App, Digest}
+	if len(payload) < MaxChunk {
+		return [][]byte{append(digest, payload...)}
+	}
+
+	// large payload is multi-chunk
+	result := [][]byte{{App, Init}}
+	update := []byte{App, Update}
+	for len(payload) > MaxChunk {
+		msg := append(update, payload[:MaxChunk]...)
+		payload = payload[MaxChunk:]
+		result = append(result, msg)
+	}
+	result = append(result, append(update, payload...))
+	result = append(result, digest)
+	return result
+}
+
+func parseDigest(resp []byte) (key, sig []byte, err error) {
+	if resp[0] != App || resp[1] != Digest {
+		return nil, nil, errors.New("Invalid header")
+	}
+	resp = resp[2:]
+	if len(resp) != KeyLength+SigLength+len(separator) {
+		return nil, nil, errors.Errorf("Incorrect length: %d", len(resp))
+	}
+
+	key, resp = resp[:KeyLength], resp[KeyLength:]
+	if !bytes.Equal(separator, resp[:len(separator)]) {
+		return nil, nil, errors.New("Cannot find 0xCAFE")
+	}
+	fmt.Println("successs")
+
+	sig = resp[len(separator):]
+	return key, sig, nil
+}
diff --git a/nano/sign_test.go b/nano/sign_test.go
new file mode 100644
index 000000000..8029ef828
--- /dev/null
+++ b/nano/sign_test.go
@@ -0,0 +1,51 @@
+package nano
+
+import (
+	"encoding/hex"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestParseDigest(t *testing.T) {
+	assert, require := assert.New(t), require.New(t)
+
+	cases := []struct {
+		output string
+		key    string
+		sig    string
+		valid  bool
+	}{
+		{
+			output: "800204338EB1DD3CCDEE1F6FB586F66E640F56FFDD14537A3F0ED9EEEDF10B528FE4195FD17AC9EDAE9718A50196A1459E2434C1E53F1238F4CFDF177FAFBA8B39249B00CAFE00FFDEA42A699205B217004E7E2FFB884E174A548D644116F4B20469CBC32F60A9CB0EEB5BB6A7F266BD0F6A0A99A45B4F18F0F477AED7C854C404EF43530DAB00",
+			key:    "04338EB1DD3CCDEE1F6FB586F66E640F56FFDD14537A3F0ED9EEEDF10B528FE4195FD17AC9EDAE9718A50196A1459E2434C1E53F1238F4CFDF177FAFBA8B39249B",
+			sig:    "FFDEA42A699205B217004E7E2FFB884E174A548D644116F4B20469CBC32F60A9CB0EEB5BB6A7F266BD0F6A0A99A45B4F18F0F477AED7C854C404EF43530DAB00",
+			valid:  true,
+		},
+		{
+			output: "800235467890876543525437890796574535467890",
+			key:    "",
+			sig:    "",
+			valid:  false,
+		},
+	}
+
+	for i, tc := range cases {
+		msg, err := hex.DecodeString(tc.output)
+		require.Nil(err, "%d: %+v", i, err)
+
+		lKey, lSig, err := parseDigest(msg)
+		if !tc.valid {
+			assert.NotNil(err, "%d", i)
+		} else if assert.Nil(err, "%d: %+v", i, err) {
+			key, err := hex.DecodeString(tc.key)
+			require.Nil(err, "%d: %+v", i, err)
+			sig, err := hex.DecodeString(tc.sig)
+			require.Nil(err, "%d: %+v", i, err)
+
+			assert.Equal(key, lKey, "%d", i)
+			assert.Equal(sig, lSig, "%d", i)
+		}
+	}
+}