diff --git a/Makefile b/Makefile
index 9806464357e0..8b40987234a0 100644
--- a/Makefile
+++ b/Makefile
@@ -1016,7 +1016,7 @@ quiet_cmd_lzma = LZMA    $@
 cmd_lzma = lzma -c -z -k -9 $< > $@
 
 quiet_cmd_fdtsig = FDTSIG  $@
-cmd_fdtsig = $(srctree)/tools/fdtsig.sh $(CONFIG_EFI_PKEY_FILE) $@
+cmd_fdtsig = $(objtree)/tools/fdtsig -K $(CONFIG_EFI_PKEY_FILE) -D $@
 
 cfg: u-boot.cfg
 
diff --git a/tools/Makefile b/tools/Makefile
index 71a52719620c..e6fd1dbade19 100644
--- a/tools/Makefile
+++ b/tools/Makefile
@@ -234,6 +234,8 @@ HOSTCFLAGS_asn1_compiler.o = -idirafter $(srctree)/include
 ifneq ($(CONFIG_EFI_CAPSULE_AUTHENTICATE),)
 HOSTLDLIBS_mkeficapsule += \
 	$(shell pkg-config --libs libssl libcrypto 2> /dev/null || echo "-lssl -lcrypto")
+	fdtsig-objs	:= fdtsig.o $(LIBFDT_OBJS)
+	hostprogs-y += fdtsig
 endif
 hostprogs-$(CONFIG_EFI_HAVE_CAPSULE_SUPPORT) += mkeficapsule
 
diff --git a/tools/fdtsig.c b/tools/fdtsig.c
new file mode 100644
index 000000000000..daa1e63c3b33
--- /dev/null
+++ b/tools/fdtsig.c
@@ -0,0 +1,274 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright 2021 Linaro Limited
+ * The code in this file was extracted from mkeficapsule.c
+ */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <getopt.h>
+#include <malloc.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <unistd.h>
+
+#include <sys/mman.h>
+#include <sys/stat.h>
+
+#include <linux/libfdt.h>
+
+#define SIGNATURE_NODENAME	"signature"
+#define OVERLAY_NODENAME	"__overlay__"
+
+static const char *tool_name = "fdtsig";
+
+static const char *opts_short = "D:K:Oh";
+
+static struct option options[] = {
+	{"dtb", required_argument, NULL, 'D'},
+	{"public key", required_argument, NULL, 'K'},
+	{"overlay", no_argument, NULL, 'O'},
+	{"help", no_argument, NULL, 'h'},
+	{NULL, 0, NULL, 0},
+};
+
+static void print_usage(void)
+{
+	printf("Usage: %s [options]\n"
+	       "Options:\n"
+
+	       "\t-K, --public-key <key file> public key esl file\n"
+	       "\t-D, --dtb <dtb file>        dtb file\n"
+	       "\t-O, --overlay               the dtb file is an overlay\n"
+	       "\t-h, --help                  print a help message\n",
+	       tool_name);
+}
+
+static int fdt_add_pub_key_data(void *sptr, void *dptr, size_t key_size,
+				bool overlay)
+{
+	int parent;
+	int ov_node;
+	int frag_node;
+	int ret = 0;
+
+	if (overlay) {
+		/*
+		 * The signature would be stored in the
+		 * first fragment node of the overlay
+		 */
+		frag_node = fdt_first_subnode(dptr, 0);
+		if (frag_node == -FDT_ERR_NOTFOUND) {
+			fprintf(stderr,
+				"Couldn't find the fragment node: %s\n",
+				fdt_strerror(frag_node));
+			goto done;
+		}
+
+		ov_node = fdt_subnode_offset(dptr, frag_node, OVERLAY_NODENAME);
+		if (ov_node == -FDT_ERR_NOTFOUND) {
+			fprintf(stderr,
+				"Couldn't find the __overlay__ node: %s\n",
+				fdt_strerror(ov_node));
+			goto done;
+		}
+	} else {
+		ov_node = 0;
+	}
+
+	parent = fdt_subnode_offset(dptr, ov_node, SIGNATURE_NODENAME);
+	if (parent == -FDT_ERR_NOTFOUND) {
+		parent = fdt_add_subnode(dptr, ov_node, SIGNATURE_NODENAME);
+		if (parent < 0) {
+			ret = parent;
+			if (ret != -FDT_ERR_NOSPACE) {
+				fprintf(stderr,
+					"Couldn't create signature node: %s\n",
+					fdt_strerror(parent));
+			}
+		}
+	}
+	if (ret)
+		goto done;
+
+	/* Write the key to the FDT node */
+	ret = fdt_setprop(dptr, parent, "capsule-key",
+			  sptr, key_size);
+
+done:
+	if (ret)
+		ret = ret == -FDT_ERR_NOSPACE ? -ENOSPC : -EIO;
+
+	return ret;
+}
+
+static int add_public_key(const char *pkey_file, const char *dtb_file,
+			  bool overlay)
+{
+	int ret;
+	int srcfd = -1;
+	int destfd = -1;
+	void *sptr = NULL;
+	void *dptr = NULL;
+	off_t src_size;
+	struct stat pub_key;
+	struct stat dtb;
+
+	/* Find out the size of the public key */
+	srcfd = open(pkey_file, O_RDONLY);
+	if (srcfd == -1) {
+		fprintf(stderr, "%s: Can't open %s: %s\n",
+			__func__, pkey_file, strerror(errno));
+		ret = -1;
+		goto err;
+	}
+
+	ret = fstat(srcfd, &pub_key);
+	if (ret == -1) {
+		fprintf(stderr, "%s: Can't stat %s: %s\n",
+			__func__, pkey_file, strerror(errno));
+		ret = -1;
+		goto err;
+	}
+
+	src_size = pub_key.st_size;
+
+	/* mmap the public key esl file */
+	sptr = mmap(0, src_size, PROT_READ, MAP_SHARED, srcfd, 0);
+	if (sptr == MAP_FAILED) {
+		fprintf(stderr, "%s: Failed to mmap %s:%s\n",
+			__func__, pkey_file, strerror(errno));
+		ret = -1;
+		goto err;
+	}
+
+	/* Open the dest FDT */
+	destfd = open(dtb_file, O_RDWR);
+	if (destfd == -1) {
+		fprintf(stderr, "%s: Can't open %s: %s\n",
+			__func__, dtb_file, strerror(errno));
+		ret = -1;
+		goto err;
+	}
+
+	ret = fstat(destfd, &dtb);
+	if (ret == -1) {
+		fprintf(stderr, "%s: Can't stat %s: %s\n",
+			__func__, dtb_file, strerror(errno));
+		goto err;
+	}
+
+	dtb.st_size += src_size + 0x30;
+	if (ftruncate(destfd, dtb.st_size)) {
+		fprintf(stderr, "%s: Can't expand %s: %s\n",
+			__func__, dtb_file, strerror(errno));
+		ret = -1;
+		goto err;
+	}
+
+	errno = 0;
+	/* mmap the dtb file */
+	dptr = mmap(0, dtb.st_size, PROT_READ | PROT_WRITE, MAP_SHARED,
+		    destfd, 0);
+	if (dptr == MAP_FAILED) {
+		fprintf(stderr, "%s: Failed to mmap %s:%s\n",
+			__func__, dtb_file, strerror(errno));
+		ret = -1;
+		goto err;
+	}
+
+	if (fdt_check_header(dptr)) {
+		fprintf(stderr, "%s: Invalid FDT header\n", __func__);
+		ret = -1;
+		goto err;
+	}
+
+	ret = fdt_open_into(dptr, dptr, dtb.st_size);
+	if (ret) {
+		fprintf(stderr, "%s: Cannot expand FDT: %s\n",
+			__func__, fdt_strerror(ret));
+		ret = -1;
+		goto err;
+	}
+
+	/* Copy the esl file to the expanded FDT */
+	ret = fdt_add_pub_key_data(sptr, dptr, src_size, overlay);
+	if (ret < 0) {
+		fprintf(stderr, "%s: Unable to add public key to the FDT\n",
+			__func__);
+		ret = -1;
+		goto err;
+	}
+
+	ret = 0;
+
+err:
+	if (sptr)
+		munmap(sptr, src_size);
+
+	if (dptr)
+		munmap(dptr, dtb.st_size);
+
+	if (srcfd != -1)
+		close(srcfd);
+
+	if (destfd != -1)
+		close(destfd);
+
+	return ret;
+}
+
+int main(int argc, char **argv)
+{
+	char *pkey_file;
+	char *dtb_file;
+	bool overlay;
+	int c, idx, ret;
+
+	pkey_file = NULL;
+	dtb_file = NULL;
+	overlay = false;
+
+	for (;;) {
+		c = getopt_long(argc, argv, opts_short, options, &idx);
+		if (c == -1)
+			break;
+
+		switch (c) {
+		case 'K':
+			if (pkey_file) {
+				printf("Public Key already specified\n");
+				return -1;
+			}
+			pkey_file = optarg;
+			break;
+		case 'D':
+			if (dtb_file) {
+				printf("DTB file already specified\n");
+				return -1;
+			}
+			dtb_file = optarg;
+			break;
+		case 'O':
+			overlay = true;
+			break;
+		case 'h':
+			print_usage();
+			return 0;
+		}
+	}
+
+	/* check necessary parameters */
+	if (!pkey_file || !dtb_file) {
+		print_usage();
+		exit(EXIT_FAILURE);
+	}
+
+	ret = add_public_key(pkey_file, dtb_file, overlay);
+	if (ret == -1) {
+		printf("Adding public key to the dtb failed\n");
+		exit(EXIT_FAILURE);
+	}
+
+	exit(EXIT_SUCCESS);
+}
