diff --git a/extras/test/CMakeLists.txt b/extras/test/CMakeLists.txt
index 0916ea6..2fb0dd0 100644
--- a/extras/test/CMakeLists.txt
+++ b/extras/test/CMakeLists.txt
@@ -26,13 +26,14 @@ set(TEST_SRCS
   src/crc32/test_crc32.cpp
   src/crc16/test_crc16.cpp
   src/sha256/test_sha256.cpp
+  src/hex/test_hex.cpp
 )
 
 set(TEST_DUT_SRCS
   ../../src/crc/crc32.cpp
   ../../src/crc/crc16.cpp
-  ../../src/sha256/SHA256.cpp
   ../../src/sha256/sha2.c
+  ../../src/hex/chex.h
 )
 
 ##########################################################################
diff --git a/extras/test/src/hex/test_hex.cpp b/extras/test/src/hex/test_hex.cpp
new file mode 100644
index 0000000..7e3a0d3
--- /dev/null
+++ b/extras/test/src/hex/test_hex.cpp
@@ -0,0 +1,53 @@
+/*
+    This file is part of the Arduino_CloudUtils library.
+
+    Copyright (c) 2024 Arduino SA
+
+    This Source Code Form is subject to the terms of the Mozilla Public
+    License, v. 2.0. If a copy of the MPL was not distributed with this
+    file, You can obtain one at http://mozilla.org/MPL/2.0/.
+*/
+
+#include <catch2/catch_test_macros.hpp>
+
+#include <hex/chex.h>
+
+SCENARIO( "HEX encoding test" ) {
+    /* check all possible 16-bit values in network byte order */
+    unsigned i;
+    for(i = 0; i <= 0xffff; ++i){
+        /* encode to hex string using our implementation */
+        const unsigned char org[2] = {(unsigned char)(i>>8), (unsigned char)i};
+        char hex[5] = {0,0,0,0,0};
+        chex_encode(hex, sizeof(hex), org, sizeof(org));
+
+        /* decode from hex string using a function from the standard library */
+        unsigned char bin[2] = {0,0};
+        int n = sscanf(hex, "%02hhx%02hhx", bin, bin+1);
+        REQUIRE(n == sizeof(bin));
+
+        /* decoded matches the original */
+        REQUIRE(memcmp(org, bin, sizeof(bin)) == 0);
+    }
+    REQUIRE(i == 0x10000);
+}
+
+SCENARIO( "HEX decoding test" ) {
+    /* check all possible 16-bit values in network byte order */
+    unsigned i;
+    for(i = 0; i <= 0xffff; ++i){
+        /* encode to hex string using a function from the standard library */
+        char hex[5] = {0,0,0,0,0};
+        snprintf(hex, sizeof(hex), "%02hhX%02hhx", (unsigned char)(i>>8), (unsigned char)i);
+
+        /* decode from hex string using our implementation */
+        unsigned char bin[2];
+        unsigned n = chex_decode(bin, sizeof(bin), hex, sizeof(hex));
+        REQUIRE(n == sizeof(bin));
+
+        /* decoded matches the original */
+        const unsigned char org[2] = {(unsigned char)(i>>8), (unsigned char)i};
+        REQUIRE(memcmp(org, bin, sizeof(bin)) == 0);
+    }
+    REQUIRE(i == 0x10000);
+}
diff --git a/src/Arduino_HEX.h b/src/Arduino_HEX.h
index 4ea9af0..c99ca04 100644
--- a/src/Arduino_HEX.h
+++ b/src/Arduino_HEX.h
@@ -10,3 +10,4 @@
 #pragma once
 
 #include "./hex/hex.h"
+using namespace hex;
diff --git a/src/bpid/bpid.cpp b/src/bpid/bpid.cpp
index 4c11130..44a3eda 100644
--- a/src/bpid/bpid.cpp
+++ b/src/bpid/bpid.cpp
@@ -41,7 +41,6 @@ namespace arduino { namespace bpid {
         uint8_t out[SHA256::HASH_SIZE];
         arduino::sha256::sha256(data, sizeof(data), out);
         return arduino::hex::encode(out, sizeof(out));
-        return String("");
     }
 
 }} // arduino::bpid
diff --git a/src/bpid/csn.cpp b/src/bpid/csn.cpp
index f0e312a..2e547f9 100644
--- a/src/bpid/csn.cpp
+++ b/src/bpid/csn.cpp
@@ -9,6 +9,7 @@
 */
 
 #include "csn.h"
+#include "hex/hex.h"
 
 namespace arduino { namespace csn {
 
@@ -22,7 +23,7 @@ namespace arduino { namespace csn {
             return false;
         }
         SecureElement se;
-        if (!se.begin() || !se.serialNumber(in)) {
+        if (!se.begin() || !arduino::hex::decode(se.serialNumber(), in, size)) {
             return false;
         }
         return true;
diff --git a/src/bpid/csn.h b/src/bpid/csn.h
index 47ef85d..795c07e 100644
--- a/src/bpid/csn.h
+++ b/src/bpid/csn.h
@@ -24,21 +24,21 @@
       defined(ARDUINO_OPTA)                || \
       defined(ARDUINO_GIGA)
     #include <Arduino_SecureElement.h>
-    #define CRYPTO_SN_SIZE 0
+    #define CRYPTO_SN_SIZE 9
 #elif defined(ARDUINO_PORTENTA_C33)        || \
       defined(ARDUINO_NICLA_VISION)
     #include <Arduino_SecureElement.h>
-    #define CRYPTO_SN_SIZE 0
+    #define CRYPTO_SN_SIZE 18
 #elif defined(ARDUINO_UNOR4_WIFI)
     #include <Arduino_SecureElement.h>
-    #define CRYPTO_SN_SIZE 0
+    #define CRYPTO_SN_SIZE 6
 #else
     #define CRYPTO_SN_SIZE 0
 #endif
 
 namespace arduino { namespace csn {
     /*
-     * This library contains the methods to get board microcontroller id
+     * This library contains the methods to get crypto serial number
      */
 
     bool get(uint8_t *in, uint32_t size);
diff --git a/src/bpid/ucid.h b/src/bpid/ucid.h
index 4fca022..560f3b3 100644
--- a/src/bpid/ucid.h
+++ b/src/bpid/ucid.h
@@ -12,12 +12,12 @@
 
 #include <Arduino.h>
 
-#if   defined(ARDUINO_SAMD_NANO_33_IOT)    || \
-      defined(ARDUINO_SAMD_MKRWIFI1010)    || \
-      defined(ARDUINO_SAMD_MKRGSM1400)     || \
-      defined(ARDUINO_SAMD_MKRWAN1300)     || \
-      defined(ARDUINO_SAMD_MKRWAN1310)     || \
-      defined(ARDUINO_SAMD_MKRNB1500)      || \
+#if   defined(ARDUINO_SAMD_NANO_33_IOT) || \
+      defined(ARDUINO_SAMD_MKRWIFI1010) || \
+      defined(ARDUINO_SAMD_MKRGSM1400)  || \
+      defined(ARDUINO_SAMD_MKRWAN1300)  || \
+      defined(ARDUINO_SAMD_MKRWAN1310)  || \
+      defined(ARDUINO_SAMD_MKRNB1500)   || \
       defined(ARDUINO_SAMD_MKR1000)
     #define UC_UID_SIZE 16
 #elif defined(ARDUINO_PORTENTA_H7_M7)   || \
diff --git a/src/hex/README.md b/src/hex/README.md
new file mode 100644
index 0000000..31f1d17
--- /dev/null
+++ b/src/hex/README.md
@@ -0,0 +1,3 @@
+# chex
+
+[chex.h](chex.h) file implement hex encoding/decoding basic functions by Tero 'stedo' Liukko under a MIT license.  https://github.com/stedonet/chex
\ No newline at end of file
diff --git a/src/hex/chex.h b/src/hex/chex.h
new file mode 100644
index 0000000..692e911
--- /dev/null
+++ b/src/hex/chex.h
@@ -0,0 +1,104 @@
+/*
+MIT License
+
+Copyright (c) 2022 Tero 'stedo' Liukko. https://github.com/stedonet/chex
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+*/
+
+#ifndef STEDO_CHEX_H
+#define STEDO_CHEX_H
+
+/**
+ * @brief check whether given ASCII character is a hexadecimal digit
+ * @param[in] h ASCII character to decode
+ * @return TRUE if h is hexadecimal, FALSE otherwise
+**/
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wunused-function"
+static unsigned chex_isxdigit(unsigned h){
+  unsigned char n09 = h - '0';
+  unsigned char nAF = (h | 0x20) - 'a';
+  return (n09 <= (9 - 0)) || (nAF <= (0xf - 0xa));
+}
+#pragma GCC diagnostic pop
+
+/**
+ * @brief encode nibble to hexadecimal ASCII character
+ * @param[in] nibble value to encode
+ * @return hexadecimal ASCII value
+ * @note the four most significant bits are ignored
+**/
+static char chex_toxdigit(unsigned nibble){
+  const char* lut = "0123456789abcdef";
+  return lut[nibble & 0xf];
+}
+
+
+/**
+ * @brief decode a single case-insensitive hexadecimal ASCII character to its decimal value
+ * @param[in] h ASCII character to decode
+ * @return decimal value of the input
+ * @note the input is assumed to be a valid
+**/
+static unsigned char chex_fromxdigit(unsigned h){
+  return ((h & 0xf) + (h >> 6) * 9);
+}
+
+
+/**
+ * @brief encode an array of bytes to an array of hexadecimal ASCII characters
+ * @param[out]  hex   buffer to write to
+ * @param[in]   hlen  maximum number of characters to write
+ * @param[in]   bin   array of bytes to encode
+ * @param[in]   blen  number of bytes to encode
+ * @return number of characters written
+ * @note null terminator is not included in the output
+**/
+static unsigned chex_encode(char* hex, unsigned hlen, const void* bin, unsigned blen){
+  const unsigned char* b = (const unsigned char*)bin;
+  unsigned i, j;
+  for(i = 0, j = 0; (i < blen) && (j+1 < hlen); ++i, j+=2){
+    hex[j+0] = chex_toxdigit(b[i]>>4);
+    hex[j+1] = chex_toxdigit(b[i]>>0);
+  }
+  return j;
+}
+
+
+/**
+ * @brief decode an array of hexadecimal ASCII characters to an array of bytes
+ * @param[out]  bin   buffer to write to
+ * @param[in]   blen  maximum number of bytes to write
+ * @param[in]   hex   array of hex characters to decode
+ * @param[in]   hlen  number of hex characters to decode
+ * @return number of bytes written
+ * @note hex input is assumed valid and its length a multiple of two
+**/
+static unsigned chex_decode(void* bin, unsigned blen, const char* hex, unsigned hlen){
+  unsigned i, j;
+  for(i = 0, j = 0; (i < blen) && (j+1 < hlen); ++i, j+=2){
+    unsigned char hi = chex_fromxdigit(hex[j+0]);
+    unsigned char lo = chex_fromxdigit(hex[j+1]);
+    ((unsigned char*)bin)[i] = (hi << 4) | lo;
+  }
+  return i;
+}
+
+#endif /* STEDO_CHEX_H */
diff --git a/src/hex/hex.cpp b/src/hex/hex.cpp
index a5c33fa..8631126 100644
--- a/src/hex/hex.cpp
+++ b/src/hex/hex.cpp
@@ -9,18 +9,30 @@
 */
 
 #include "hex.h"
+#include "chex.h"
 
 namespace arduino { namespace hex {
 
-    String encode(uint8_t* in, uint32_t size) {
-        String out;
-        out.reserve((size * 2) + 1);
+    String encode(const uint8_t* in, uint32_t size) {
+        char out[(size * 2) + 1];
+        unsigned int byteNumber;
+        byteNumber = chex_encode(out, sizeof(out), in, size);
+        out[byteNumber] = 0;
+        return String(out);
+    }
+
+    String encodeUpper(const uint8_t* in, uint32_t size) {
+        String out = encode(in, size);
+        out.toUpperCase();
+        return out;
+    }
 
-        char *ptr = out.begin();
-        for (uint32_t i = 0; i < size; i++) {
-            ptr += sprintf(ptr, "%02X", in[i]);
-        }
-        return String(out.c_str());
+    bool decode(const String in, uint8_t* out, uint32_t size) {
+        unsigned int byteNumber;
+        byteNumber = chex_decode(out, size, in.begin(), in.length());
+        Serial.println(byteNumber);
+        Serial.println(in.length());
+        return byteNumber * 2  == in.length();
     }
 
 }} // arduino::hex
diff --git a/src/hex/hex.h b/src/hex/hex.h
index d3f94c5..8d85c39 100644
--- a/src/hex/hex.h
+++ b/src/hex/hex.h
@@ -14,9 +14,29 @@
 
 namespace arduino { namespace hex {
     /*
-     * This library contains the methods to get board provisioning id
+     * This library contains the methods to hex encode a buffer into a String
+     * and vice-versa
      */
 
-    String encode(uint8_t* in, uint32_t size);
+    String encode(const uint8_t* in, uint32_t size);
+    String encodeUpper(const uint8_t* in, uint32_t size);
+
+    bool decode(const String in, uint8_t* out, uint32_t size);
+
+    class THEXT {
+
+    public:
+        static inline String encode(const uint8_t* in, uint32_t size) {
+            return arduino::hex::encode(in, size);
+        }
+        static inline String encodeUpper(const uint8_t* in, uint32_t size) {
+            return arduino::hex::encodeUpper(in, size);
+        }
+
+        static inline bool decode(const String in, uint8_t* out, uint32_t size) {
+            return arduino::hex::decode(in, out, size);
+        }
+
+    };
 
 }} // arduino::hex