Allow appending to notes

Right now it's n^2 which is a big problem (to be fixed later)

1 files changed, 18 insertions, 8 deletions

diff --git a/internal/cryptoutil/cryptoutil.go b/internal/cryptoutil/cryptoutil.go
index b269803..0429b02 100644
--- a/internal/cryptoutil/cryptoutil.go
+++ b/internal/cryptoutil/cryptoutil.go
@@ -9,8 +9,10 @@ import (
 	"crypto/rand"
 	"crypto/sha512"
 	"crypto/subtle"
+	"encoding/binary"
 	"encoding/hex"
 	"errors"
+	"io"
 )
 
 const (
@@ -101,23 +103,31 @@ func (h PasswordHash) CheckPassword(password string) (RawKey, error) {
 	return key, nil
 }
 
-// Sign generates an HMAC-SHA512 signature and appends it to msg.
-func (k HMACKey) Sign(msg []byte) SignedMessage {
+func (k HMACKey) mac(out, msg []byte, info string) []byte {
 	mac := hmac.New(sha512.New, k)
+	buf := make([]byte, 0, binary.MaxVarintLen64)
+	mac.Write(binary.AppendUvarint(buf, uint64(len(info))))
+	io.WriteString(mac, info)
 	mac.Write(msg)
-	return mac.Sum(msg)
+	return mac.Sum(out)
+}
+
+// Sign generates an HMAC-SHA512 signature and appends it to msg. The info and
+// additionalData are also authenticated, but are not included in the returned
+// signed message.
+func (k HMACKey) Sign(msg []byte, info string) SignedMessage {
+	return k.mac(msg, msg, info)
 }
 
 // Verify checks whether the given message has a valid signature, and returns
-// the raw message if it does.
-func (k HMACKey) Verify(msg SignedMessage) ([]byte, bool) {
+// the raw message if it does. The additionalData must match the data passed
+// to Sign.
+func (k HMACKey) Verify(msg SignedMessage, info string) ([]byte, bool) {
 	if len(msg) < certSize {
 		return nil, false
 	}
 	msg, sig := msg[:len(msg)-certSize], msg[len(msg)-certSize:]
-	mac := hmac.New(sha512.New, k)
-	mac.Write(msg)
-	if !hmac.Equal(sig, mac.Sum(nil)) {
+	if !hmac.Equal(sig, k.mac(nil, msg, info)) {
 		return nil, false
 	}
 	return msg, true