diff --git a/client/cmdhffido.c b/client/cmdhffido.c
index b4b6c058..dbe05ffe 100644
--- a/client/cmdhffido.c
+++ b/client/cmdhffido.c
@@ -26,13 +26,17 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <ctype.h>
+#include <unistd.h>
+#include <jansson.h>
 #include "comms.h"
 #include "cmdmain.h"
 #include "util.h"
 #include "ui.h"
+#include "proxmark3.h"
 #include "cmdhf14a.h"
 #include "mifare.h"
 #include "emv/emvcore.h"
+#include "emv/emvjson.h"
 #include "emv/dump.h"
 #include "cliparser/cliparser.h"
 
@@ -142,6 +146,8 @@ int CmdHFFidoRegister(const char *cmd) {
 	uint8_t cdata[250] = {0};
 	int applen = 0;
 	uint8_t adata[250] = {0};
+	json_t *root = NULL;
+	json_error_t error;
 	
 	CLIParserInit("hf fido reg", 
 		"Initiate a U2F token registration. Needs two 32-byte hash number. \nchallenge parameter (32b) and application parameter (32b).", 
@@ -154,6 +160,7 @@ int CmdHFFidoRegister(const char *cmd) {
 		arg_lit0("aA",  "apdu",     "show APDU reqests and responses"),
 		arg_lit0("vV",  "verbose",  "show technical data"),
 		arg_lit0("pP",  "plain",    "send plain ASCII to challenge and application parameters instead of HEX"),
+		arg_str0("jJ",  "json",		"fido.json", "JSON input / output file name for parameters."),
 		arg_str0(NULL,  NULL,       "<HEX/ASCII challenge parameter (32b HEX/1..16 chars)>", NULL),
 		arg_str0(NULL,  NULL,       "<HEX/ASCII application parameter (32b HEX/1..16 chars)>", NULL),
 		arg_param_end
@@ -163,15 +170,45 @@ int CmdHFFidoRegister(const char *cmd) {
 	bool APDULogging = arg_get_lit(1);
 	bool verbose = arg_get_lit(2);
 	bool paramsPlain = arg_get_lit(3);
+
+	uint8_t jsonname[250] ={0};
+	char *cjsonname = (char *)jsonname;
+	int jsonnamelen = 0;
+	CLIGetStrWithReturn(4, jsonname, &jsonnamelen);
+	// current path + file name
+	if (!strstr(cjsonname, ".json"))
+		strcat(cjsonname, ".json");
+	char fname[strlen(get_my_executable_directory()) + strlen(cjsonname) + 1];
+	if (jsonnamelen) {
+		strcpy(fname, get_my_executable_directory());
+		strcat(fname, cjsonname);
+		if (access(fname, F_OK) != -1) {
+			root = json_load_file(fname, 0, &error);
+			if (!root) {
+				PrintAndLog("ERROR: json error on line %d: %s", error.line, error.text);
+				return 1; 
+			}
+			
+			if (!json_is_object(root)) {
+				PrintAndLog("ERROR: Invalid json format. root must be an object.");
+				return 1; 
+			}
+			
+			
+		} else {
+			root = json_object();
+		}
+	}
+
 	if (paramsPlain) {
 		memset(cdata, 0x00, 32);
-		CLIGetStrWithReturn(4, cdata, &chlen);
+		CLIGetStrWithReturn(5, cdata, &chlen);
 		if (chlen && chlen > 16) {
 			PrintAndLog("ERROR: challenge parameter length in ASCII mode must be less than 16 chars instead of: %d", chlen);
 			return 1;
 		}
 	} else {
-		CLIGetHexWithReturn(4, cdata, &chlen);
+		CLIGetHexWithReturn(5, cdata, &chlen);
 		if (chlen && chlen != 32) {
 			PrintAndLog("ERROR: challenge parameter length must be 32 bytes only.");
 			return 1;
@@ -183,13 +220,13 @@ int CmdHFFidoRegister(const char *cmd) {
 	
 	if (paramsPlain) {
 		memset(adata, 0x00, 32);
-		CLIGetStrWithReturn(5, adata, &applen);
+		CLIGetStrWithReturn(6, adata, &applen);
 		if (applen && applen > 16) {
 			PrintAndLog("ERROR: application parameter length in ASCII mode must be less than 16 chars instead of: %d", applen);
 			return 1;
 		}
 	} else {
-		CLIGetHexWithReturn(5, adata, &applen);
+		CLIGetHexWithReturn(6, adata, &applen);
 		if (applen && applen != 32) {
 			PrintAndLog("ERROR: application parameter length must be 32 bytes only.");
 			return 1;
@@ -280,6 +317,24 @@ int CmdHFFidoRegister(const char *cmd) {
 		printf(" %s", paramsPlain?(char *)adata:sprint_hex_inrow(adata, 32));
 	printf("\n");
 	
+	if (root) {
+		JsonSaveBufAsHex(root, "ChallengeParam", data, 32);
+		JsonSaveBufAsHex(root, "ApplicationParam", &data[32], 32);
+		JsonSaveInt(root, "KeyHandleLen", keyHandleLen);
+		JsonSaveBufAsHexCompact(root, "KeyHandle", &buf[67], keyHandleLen);
+		JsonSaveBufAsHexCompact(root, "DER", &buf[67 + keyHandleLen], derLen);
+	
+		res = json_dump_file(root, fname, JSON_INDENT(2));
+		if (res) {
+			PrintAndLog("ERROR: can't save the file: %s", fname);
+			return 200;
+		}
+		PrintAndLog("File `%s` saved.", fname);
+		
+		// free json object
+		json_decref(root);
+	}
+	
 	return 0;
 };
 
diff --git a/client/emv/emvjson.c b/client/emv/emvjson.c
index 02297435..9defce08 100644
--- a/client/emv/emvjson.c
+++ b/client/emv/emvjson.c
@@ -68,24 +68,40 @@ char* GetApplicationDataName(tlv_tag_t tag) {
 	return NULL;
 }
 
-int JsonSaveStr(json_t *root, char *path, char *value) {
+int JsonSaveJsonObject(json_t *root, char *path, json_t *value) {
 	json_error_t error;
 
 	if (strlen(path) < 1)
 		return 1;
 	
 	if (path[0] == '$') {
-		if (json_path_set(root, path, json_string(value), 0, &error)) {
+		if (json_path_set(root, path, value, 0, &error)) {
 			PrintAndLog("ERROR: can't set json path: ", error.text);
 			return 2;
 		} else {
 			return 0;
 		}
 	} else {
-		return json_object_set_new(root, path, json_string(value));
+		return json_object_set_new(root, path, value);
 	}
+}
+
+int JsonSaveInt(json_t *root, char *path, int value) {
+	return JsonSaveJsonObject(root, path, json_integer(value));
+}
+
+int JsonSaveStr(json_t *root, char *path, char *value) {
+	return JsonSaveJsonObject(root, path, json_string(value));
 };
 
+int JsonSaveBufAsHexCompact(json_t *elm, char *path, uint8_t *data, size_t datalen) {
+	char * msg = sprint_hex_inrow(data, datalen);
+	if (msg && strlen(msg) && msg[strlen(msg) - 1] == ' ')
+		msg[strlen(msg) - 1] = '\0';
+
+	return JsonSaveStr(elm, path, msg);
+}
+
 int JsonSaveBufAsHex(json_t *elm, char *path, uint8_t *data, size_t datalen) {
 	char * msg = sprint_hex(data, datalen);
 	if (msg && strlen(msg) && msg[strlen(msg) - 1] == ' ')
@@ -248,6 +264,11 @@ bool HexToBuffer(const char *errormsg, const char *hexvalue, uint8_t * buffer, s
 	return true;
 }
 
+int JsonLoadBufAsHex(json_t *elm, char *path, uint8_t *data, size_t *datalen) {
+	
+	return 0;
+};
+
 bool ParamLoadFromJson(struct tlvdb *tlv) {
 	json_t *root;
 	json_error_t error;
diff --git a/client/emv/emvjson.h b/client/emv/emvjson.h
index a518d7b9..7148ddd0 100644
--- a/client/emv/emvjson.h
+++ b/client/emv/emvjson.h
@@ -20,7 +20,10 @@ typedef struct {
 
 extern char* GetApplicationDataName(tlv_tag_t tag);
 
+extern int JsonSaveJsonObject(json_t *root, char *path, json_t *value);
 extern int JsonSaveStr(json_t *root, char *path, char *value);
+extern int JsonSaveInt(json_t *root, char *path, int value);
+extern int JsonSaveBufAsHexCompact(json_t *elm, char *path, uint8_t *data, size_t datalen);
 extern int JsonSaveBufAsHex(json_t *elm, char *path, uint8_t *data, size_t datalen);
 extern int JsonSaveHex(json_t *elm, char *path, uint64_t data, int datalen);
 
@@ -30,6 +33,8 @@ extern int JsonSaveTLVTreeElm(json_t *elm, char *path, struct tlvdb *tlvdbelm, b
 
 extern int JsonSaveTLVTree(json_t *root, json_t *elm, char *path, struct tlvdb *tlvdbelm);
 
+extern int JsonLoadBufAsHex(json_t *elm, char *path, uint8_t *data, size_t *datalen);
+
 extern bool ParamLoadFromJson(struct tlvdb *tlv);
 
 #endif
\ No newline at end of file
diff --git a/client/util.c b/client/util.c
index d7c824d9..c6d5f0d6 100644
--- a/client/util.c
+++ b/client/util.c
@@ -139,7 +139,7 @@ void hex_to_buffer(const uint8_t *buf, const uint8_t *hex_data, const size_t hex
 // printing and converting functions
 
 char *sprint_hex(const uint8_t *data, const size_t len) {
-	static char buf[1025] = {0};
+	static char buf[4097] = {0};
 	
 	hex_to_buffer((uint8_t *)buf, data, len, sizeof(buf) - 1, 0, 1, false);
 
@@ -147,7 +147,7 @@ char *sprint_hex(const uint8_t *data, const size_t len) {
 }
 
 char *sprint_hex_inrow_ex(const uint8_t *data, const size_t len, const size_t min_str_len) {
-	static char buf[1025] = {0};
+	static char buf[4097] = {0};
 
 	hex_to_buffer((uint8_t *)buf, data, len, sizeof(buf) - 1, min_str_len, 0, false);