diff --git a/tools/sdfsign.c b/tools/sdfsign.c
index bc83b3f8..e1434b76 100644
--- a/tools/sdfsign.c
+++ b/tools/sdfsign.c
@@ -32,7 +32,7 @@ static const char *options =
 "Examples\n"
 "\n"
 "    $ echo -n 'message to be signed' | gmssl sdfsign -lib libsoftsdf.so -key 1 -pass P@ssw0rd -out sm2.sig\n"
-"    $ gmssl sdfexport -lib libsoftsdf.so -key 1 -out sm2pub.pem\n"
+"    $ gmssl sdfexport -lib libsoftsdf.so -sign -key 1 -out sm2pub.pem\n"
 "    $ echo -n 'message to be signed' | gmssl sm2verify -pubkey sm2pub.pem -sig sm2.sig\n"
 "\n";
 
@@ -74,6 +74,16 @@ int sdfsign_main(int argc, char **argv)
 		} else if (!strcmp(*argv, "-lib")) {
 			if (--argc < 1) goto bad;
 			lib = *(++argv);
+		} else if (!strcmp(*argv, "-key")) {
+			if (--argc < 1) goto bad;
+			key_index = atoi(*(++argv));
+			if (key_index < 0) {
+				fprintf(stderr, "gmssl %s: illegal key index %d\n", prog, key_index);
+				goto end;
+			}
+		} else if (!strcmp(*argv, "-pass")) {
+			if (--argc < 1) goto bad;
+			pass = *(++argv);
 		} else if (!strcmp(*argv, "-id")) {
 			if (--argc < 1) goto bad;
 			id = *(++argv);