Fix cosig timestamp endianness (#153)

note/note_cosigv1.go

@@ -70,7 +70,7 @@ func NewSignerForCosignatureV1(skey string) (*Signer, error) {
 
 			// The signature itself is encoded as timestamp || signature.
 			sig := make([]byte, 0, timestampSize+ed25519.SignatureSize)
-			sig = binary.LittleEndian.AppendUint64(sig, t)
+			sig = binary.BigEndian.AppendUint64(sig, t)
 			sig = append(sig, ed25519.Sign(key, m)...)
 			return sig, nil
 		}
@@ -124,7 +124,7 @@ func CoSigV1Timestamp(s note.Signature) (time.Time, error) {
 	}
 	r = r[keyHashSize:] // Skip the hash
 	// Next 8 bytes are the timestamp as Unix seconds-since-epoch:
-	return time.Unix(int64(binary.LittleEndian.Uint64(r)), 0), nil
+	return time.Unix(int64(binary.BigEndian.Uint64(r)), 0), nil
 }
 
 // verifyCosigV1 returns a verify function based on key.
@@ -133,7 +133,7 @@ func verifyCosigV1(key []byte) func(msg, sig []byte) bool {
 		if len(sig) != timestampSize+ed25519.SignatureSize {
 			return false
 		}
-		t := binary.LittleEndian.Uint64(sig)
+		t := binary.BigEndian.Uint64(sig)
 		sig = sig[timestampSize:]
 		m, err := formatCosignatureV1(t, msg)
 		if err != nil {

note/note_cosigv1_test.go

@@ -154,8 +154,8 @@ func TestCoSigV1Timestamp(t *testing.T) {
 	}{
 		{
 			name:     "works",
-			sig:      note.Signature{Base64: "W+8PSVYlTmUAAAAAOUcMpZzRiZaiZRr94NylbaFKHqXu5KQbk70RPuCZVi3PkU8GZJpCQYgyqjnmuSRCShglqdlUZGUplgn7ECavCA=="},
-			wantTime: time.Unix(1699620182, 0),
+			sig:      note.Signature{Base64: "ZGhGuQAAAABm/qTPeyKXD+R2rzyQsxPiP8mXum7qq/iF0u4vanlqJyocWODBt97w9uL+8qT7S5gxEHWWOworDcFiEBYJXORmnFBOBA=="},
+			wantTime: time.Unix(1727964367, 0),
 		}, {
 			name:    "wrong type of signature",
 			sig:     note.Signature{Base64: "eQjRQm6eSKzFoiYalgwCPXu2y3ijtg68is9M46JKxuZB+dRfTmeQeDBoXnvxZx2ugnkyV+MUMLXpWs1hPb/W/4xkNQY="},