diff --git a/libraries/MySensors/MyConfig.h b/libraries/MySensors/MyConfig.h
index 82c02da..0ffab4e 100644
--- a/libraries/MySensors/MyConfig.h
+++ b/libraries/MySensors/MyConfig.h
@@ -18,6 +18,7 @@
 // Choose signing backend by enabling one of the following
 #define MYSENSORS_SIGNING_DUMMY
 //#define MYSENSORS_SIGNING_ATSHA204
+//#define MYSENSORS_SIGNING_ATSHA204SOFT
 
 // Define a suitable timeout for a signature verification session
 // Consider the turnaround from a nonce being generated to a signed message being received
@@ -58,6 +59,33 @@ typedef class MySigningDriverDummy MySigningDriverClass;
 typedef class MySigningDriverAtsha204 MySigningDriverClass;
 #endif
 
+#ifdef MYSENSORS_SIGNING_ATSHA204SOFT
+// Key to use for HMAC calculation
+static uint8_t hmacKey[32] = {
+0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
+0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
+0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,
+0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00
+};
+
+// Pick an unconnected analog pin for RANDOMSEED_PIN
+#ifdef MYSENSORS_SENSOR
+#define RANDOMSEED_PIN 7 //A7
+#endif
+
+#ifdef MYSENSORS_SERIAL_GATEWAY
+#define RANDOMSEED_PIN 7 //A7
+#endif
+
+#ifdef MYSENSORS_ETHERNET_MQTT_GATEWAY
+#define RANDOMSEED_PIN 7 //A7
+#endif
+
+#include "MySigningDriverAtsha204Soft.h"
+#define SIGNING_IDENTIFIER (1) // SHA256-based HMAC (ATSHA204 specific)
+typedef class MySigningDriverAtsha204Soft MySigningDriverClass;
+#endif
+
 /***
  * Enable/Disable debug logging
  */
diff --git a/libraries/MySensors/MySigningDriverAtsha204Soft.cpp b/libraries/MySensors/MySigningDriverAtsha204Soft.cpp
new file mode 100644
index 0000000..aaff71f
--- /dev/null
+++ b/libraries/MySensors/MySigningDriverAtsha204Soft.cpp
@@ -0,0 +1,225 @@
+/*
+ ATSHA204 emulated signing backend. The emulated ATSHA204 implementation offers pseudo random
+ number generation and HMAC-SHA256 authentication compatible with a "physical" ATSHA204.
+ NOTE: Key is stored in clear text in the Arduino firmware. Therefore, the use of this back-end
+ could compromise the key used in the signed message infrastructure if device is lost and its memory
+ dumped.
+ 
+ Created by Patrick "Anticimex" Fallberg <patrick@fallberg.net>
+*/
+#include "MySigningDriver.h"
+#include "MySigningDriverAtsha204Soft.h"
+#include "sha256.h"
+
+#ifdef MYSENSORS_SIGNING_ATSHA204SOFT
+// Uncomment this to get some useful serial debug info (Serial.print and Serial.println expected)
+//#define DEBUG_ATSHASOFT_SIGNING
+
+#ifdef DEBUG_ATSHASOFT_SIGNING
+#define DEBUG_ATSHASOFT_PRINTLN(args) Serial.println(args)
+#else
+#define DEBUG_ATSHASOFT_PRINTLN(args)
+#endif
+
+#ifdef DEBUG_ATSHASOFT_SIGNING
+static void DEBUG_ATSHASOFT_PRINTBUF(char* str, uint8_t* buf, uint8_t sz)
+{
+	int i;
+	Serial.println(str);
+	for (int i=0; i<sz; i++)
+	{
+		if (buf[i] < 0x10)
+		{
+			Serial.print('0'); // Because Serial.print does not 0-pad HEX
+		}
+		Serial.print(buf[i], HEX);
+	}
+	Serial.println();
+}
+#else
+#define DEBUG_ATSHASOFT_PRINTBUF(str, buf, sz)
+#endif
+
+static Sha256Class Sha256;
+
+MySigningDriverAtsha204Soft::MySigningDriverAtsha204Soft() : MySigningDriver() {
+	verification_ongoing = false;
+
+	// We set the part of the 32-byte nonce that does not fit into a message to 0xAA
+	memset(current_nonce, 0xAA, sizeof(current_nonce));
+}
+
+bool MySigningDriverAtsha204Soft::getNonce(MyMessage &msg) {
+	// Set randomseed
+	randomSeed(analogRead(RANDOMSEED_PIN));
+	for (int i = 0; i < MAX_PAYLOAD; i++)
+	{
+		current_nonce[i] = random(255);
+	}
+	current_nonce[0] = SIGNING_IDENTIFIER;
+	
+	// Transfer the first part of the nonce to the message
+	msg.set(current_nonce, MAX_PAYLOAD);
+	verification_ongoing = true;
+	timestamp = millis(); // Set timestamp to determine when to purge nonce
+	// Be a little fancy to handle turnover (prolong the time allowed to timeout after turnover)
+	// Note that if message is "too" quick, and arrives before turnover, it will be rejected
+	// but this is consider such a rare case that it is accepted and rejects are 'safe'
+	if (timestamp + VERIFICATION_TIMEOUT_MS < millis()) timestamp = 0;
+	return true;
+}
+
+bool MySigningDriverAtsha204Soft::checkTimer() {
+	if (verification_ongoing) {
+		if (millis() < timestamp || millis() > timestamp + VERIFICATION_TIMEOUT_MS) {
+			DEBUG_ATSHASOFT_PRINTLN("Verification timeout");
+			// Purge nonce
+			memset(current_nonce, 0xAA, 32);
+			verification_ongoing = false;
+			return false; 
+		}
+	}
+	return true;
+}
+
+bool MySigningDriverAtsha204Soft::putNonce(MyMessage &msg) {
+	if (mGetLength(msg) != MAX_PAYLOAD) {
+		DEBUG_ATSHASOFT_PRINTLN("Incoming nonce with incorrect size");
+		return false; // We require as big nonce as possible
+	}
+
+	if (((uint8_t*)msg.getCustom())[0] != SIGNING_IDENTIFIER) {
+		DEBUG_ATSHASOFT_PRINTLN("Incorrect signing identifier");
+		return false; 
+	}
+
+	memcpy(current_nonce, (uint8_t*)msg.getCustom(), MAX_PAYLOAD);
+	return true;
+}
+
+bool MySigningDriverAtsha204Soft::signMsg(MyMessage &msg) {
+	// If we cannot fit any signature in the message, refuse to sign it
+	if (mGetLength(msg) > MAX_PAYLOAD-2) {
+		DEBUG_ATSHASOFT_PRINTLN("Cannot fit any signature to this message");
+		return false; 
+	}
+
+	// Calculate signature of message
+	mSetSigned(msg, 1); // make sure signing flag is set before signature is calculated
+	DEBUG_ATSHASOFT_PRINTBUF("Message to sign:", (uint8_t*)&msg.data[1-HEADER_SIZE], MAX_MESSAGE_LENGTH-1-(MAX_PAYLOAD-mGetLength(msg)));
+	if (!calculateSignature(msg)) {
+		DEBUG_ATSHASOFT_PRINTLN("Failed to calculate signature");
+		mSetSigned(msg, 0); // make sure signing flag is truthful
+		return false;
+	}
+
+	// Transfer as much signature data as the remaining space in the message permits
+	memcpy(&msg.data[mGetLength(msg)], hmac, MAX_PAYLOAD-mGetLength(msg));
+
+	return true;
+}
+
+bool MySigningDriverAtsha204Soft::verifyMsg(MyMessage &msg) {
+	if (!verification_ongoing) {
+		DEBUG_ATSHASOFT_PRINTLN("No active verification session");
+		return false; 
+	} else {
+		// Make sure we have not expired
+		if (!checkTimer()) {
+			return false; 
+		}
+
+		verification_ongoing = false;
+
+		if (msg.data[mGetLength(msg)] != SIGNING_IDENTIFIER) {
+			DEBUG_ATSHASOFT_PRINTLN("Incorrect signing identifier");
+			return false; 
+		}
+
+		DEBUG_ATSHASOFT_PRINTBUF("Message to verify:", (uint8_t*)&msg.data[1-HEADER_SIZE], MAX_MESSAGE_LENGTH-1-(MAX_PAYLOAD-mGetLength(msg)));
+		DEBUG_ATSHASOFT_PRINTBUF("Signature in message:", (uint8_t*)&msg.data[mGetLength(msg)], MAX_PAYLOAD-mGetLength(msg));
+
+		// Get signature of message
+		if (!calculateSignature(msg)) {
+			DEBUG_ATSHASOFT_PRINTLN("Failed to calculate signature");
+			return false; 
+		}
+
+		// Compare the caluclated signature with the provided signature
+		if (memcmp(&msg.data[mGetLength(msg)], hmac, MAX_PAYLOAD-mGetLength(msg))) {
+			DEBUG_ATSHASOFT_PRINTBUF("Signature bad. Calculated signature:", hmac, MAX_PAYLOAD-mGetLength(msg));
+			return false; 
+		} else {
+			DEBUG_ATSHASOFT_PRINTLN("Signature ok");
+			return true;
+		}
+	}
+}
+
+// Helper to calculate signature of msg (returned in rx_buffer[SHA204_BUFFER_POS_DATA])
+bool MySigningDriverAtsha204Soft::calculateSignature(MyMessage &msg) {
+	memset(temp_message, 0, 32);
+	memcpy(temp_message, (uint8_t*)&msg.data[1-HEADER_SIZE], MAX_MESSAGE_LENGTH-1-(MAX_PAYLOAD-mGetLength(msg)));
+
+	// ATSHA204 calculates the HMAC with a PSK and a SHA256 digest of the following data:
+	// 32 bytes zeroes
+	// 32 bytes digest,
+	// 1 byte OPCODE (0x11)
+	// 1 byte Mode (0x04)
+	// 2 bytes SlotID (0x0000)
+	// 11 bytes zeroes
+	// SN[8] (0xEE)
+	// 4 bytes zeroes
+	// SN[0:1] (0x0123)
+	// 2 bytes zeroes
+
+	// The digest is calculated as a SHA256 digest of the following:
+	// 32 bytes message
+	// 1 byte OPCODE (0x15)
+	// 1 byte param1 (0x02)
+	// 2 bytes param2 (0x0800)
+	// SN[8] (0xEE)
+	// SN[0:1] (0x0123)
+	// 25 bytes zeroes
+	// 32 bytes nonce
+
+	// Calculate message digest first
+	Sha256.init();
+	for (int i=0; i<32; i++) Sha256.write(temp_message[i]);
+	Sha256.write(0x15); // OPCODE
+	Sha256.write(0x02); // param1
+	Sha256.write(0x08); // param2(1)
+	Sha256.write(0x00); // param2(2)
+	Sha256.write(0xEE); // SN[8]
+	Sha256.write(0x01); // SN[0]
+	Sha256.write(0x23); // SN[1]
+	for (int i=0; i<25; i++) Sha256.write(0x00);
+	for (int i=0; i<32; i++) Sha256.write(current_nonce[i]);
+	// Purge nonce when used
+	memset(current_nonce, 0xAA, 32);
+	memcpy(temp_message, Sha256.result(), 32);
+
+	// Feed "message" to HMAC calculator
+	Sha256.initHmac(hmacKey,32); // Set the key to use
+	for (int i=0; i<32; i++) Sha256.write(0x00); // 32 bytes zeroes
+	for (int i=0; i<32; i++) Sha256.write(temp_message[i]); // 32 bytes digest
+	Sha256.write(0x11); // OPCODE
+	Sha256.write(0x04); // Mode
+	Sha256.write(0x00); // SlotID(1)
+	Sha256.write(0x00); // SlotID(2)
+	for (int i=0; i<11; i++) Sha256.write(0x00); // 11 bytes zeroes
+	Sha256.write(0xEE); // SN[8]
+	for (int i=0; i<4; i++) Sha256.write(0x00); // 4 bytes zeroes
+	Sha256.write(0x01); // SN[0]
+	Sha256.write(0x23); // SN[1]
+	for (int i=0; i<2; i++) Sha256.write(0x00); // 2 bytes zeroes
+
+	hmac = Sha256.resultHmac();
+
+	// Overwrite the first byte in the signature with the signing identifier
+	hmac[0] = SIGNING_IDENTIFIER;
+
+	DEBUG_ATSHASOFT_PRINTBUF("HMAC:", hmac, 32);
+	return true;
+}
+#endif
diff --git a/libraries/MySensors/MySigningDriverAtsha204Soft.h b/libraries/MySensors/MySigningDriverAtsha204Soft.h
new file mode 100644
index 0000000..16d8d3e
--- /dev/null
+++ b/libraries/MySensors/MySigningDriverAtsha204Soft.h
@@ -0,0 +1,43 @@
+/*
+ ATSHA204 emulated signing backend. The emulated ATSHA204 implementation offers pseudo random
+ number generation and HMAC-SHA256 authentication compatible with a "physical" ATSHA204.
+ NOTE: Key is stored in clear text in the Arduino firmware. Therefore, the use of this back-end
+ could compromise the key used in the signed message infrastructure if device is lost and its memory
+ dumped.
+ 
+ Created by Patrick "Anticimex" Fallberg <patrick@fallberg.net>
+*/
+#ifndef MySigningDriverHmac256Soft_h
+#define MySigningDriverHmac256Soft_h
+
+#include "MyConfig.h"
+#include "MySigningDriver.h"
+#include "utility/ATSHA204.h"
+#include <stdint.h>
+
+// This implementation is the pure software variant of the ATSHA204.
+// It is designed to work fully compliant with nodes using ATSHA204 in the network
+// and therefore uses the same signing identifier as ATSHA204.
+// Because it is completly software based, the quality of the generated random numbers
+// is weaker though. Random numbers are generated using the Arduino library and seed
+// is sampled from an analog pin. This pin should unconnected in the hardware.
+// The pin is selected using RANDOMSEED_PIN in MyConfig.h.
+class MySigningDriverAtsha204Soft : public MySigningDriver
+{ 
+public:
+	MySigningDriverAtsha204Soft();
+	bool getNonce(MyMessage &msg);
+	bool checkTimer(void);
+	bool putNonce(MyMessage &msg);
+	bool signMsg(MyMessage &msg);
+	bool verifyMsg(MyMessage &msg);
+private:
+	unsigned long timestamp;
+	bool verification_ongoing;
+	uint8_t current_nonce[NONCE_NUMIN_SIZE_PASSTHROUGH];
+	uint8_t temp_message[32];
+	uint8_t* hmac;
+	bool calculateSignature(MyMessage &msg);
+};
+
+#endif
diff --git a/libraries/MySensors/utility/sha256.cpp b/libraries/MySensors/utility/sha256.cpp
new file mode 100644
index 0000000..8434499
--- /dev/null
+++ b/libraries/MySensors/utility/sha256.cpp
@@ -0,0 +1,167 @@
+#include <string.h>
+#include <avr/io.h>
+#include <avr/pgmspace.h>
+#include "sha256.h"
+
+uint32_t sha256K[] PROGMEM = {
+  0x428a2f98,0x71374491,0xb5c0fbcf,0xe9b5dba5,0x3956c25b,0x59f111f1,0x923f82a4,0xab1c5ed5,
+  0xd807aa98,0x12835b01,0x243185be,0x550c7dc3,0x72be5d74,0x80deb1fe,0x9bdc06a7,0xc19bf174,
+  0xe49b69c1,0xefbe4786,0x0fc19dc6,0x240ca1cc,0x2de92c6f,0x4a7484aa,0x5cb0a9dc,0x76f988da,
+  0x983e5152,0xa831c66d,0xb00327c8,0xbf597fc7,0xc6e00bf3,0xd5a79147,0x06ca6351,0x14292967,
+  0x27b70a85,0x2e1b2138,0x4d2c6dfc,0x53380d13,0x650a7354,0x766a0abb,0x81c2c92e,0x92722c85,
+  0xa2bfe8a1,0xa81a664b,0xc24b8b70,0xc76c51a3,0xd192e819,0xd6990624,0xf40e3585,0x106aa070,
+  0x19a4c116,0x1e376c08,0x2748774c,0x34b0bcb5,0x391c0cb3,0x4ed8aa4a,0x5b9cca4f,0x682e6ff3,
+  0x748f82ee,0x78a5636f,0x84c87814,0x8cc70208,0x90befffa,0xa4506ceb,0xbef9a3f7,0xc67178f2
+};
+
+#define BUFFER_SIZE 64
+
+uint8_t sha256InitState[] PROGMEM = {
+  0x67,0xe6,0x09,0x6a, // H0
+  0x85,0xae,0x67,0xbb, // H1
+  0x72,0xf3,0x6e,0x3c, // H2
+  0x3a,0xf5,0x4f,0xa5, // H3
+  0x7f,0x52,0x0e,0x51, // H4
+  0x8c,0x68,0x05,0x9b, // H5
+  0xab,0xd9,0x83,0x1f, // H6
+  0x19,0xcd,0xe0,0x5b  // H7
+};
+
+void Sha256Class::init(void) {
+  memcpy_P(state.b,sha256InitState,32);
+  byteCount = 0;
+  bufferOffset = 0;
+}
+
+uint32_t Sha256Class::ror32(uint32_t number, uint8_t bits) {
+  return ((number << (32-bits)) | (number >> bits));
+}
+
+void Sha256Class::hashBlock() {
+  uint8_t i;
+  uint32_t a,b,c,d,e,f,g,h,t1,t2;
+
+  a=state.w[0];
+  b=state.w[1];
+  c=state.w[2];
+  d=state.w[3];
+  e=state.w[4];
+  f=state.w[5];
+  g=state.w[6];
+  h=state.w[7];
+  
+  for (i=0; i<64; i++) {
+    if (i>=16) {
+      t1 = buffer.w[i&15] + buffer.w[(i-7)&15];
+      t2 = buffer.w[(i-2)&15];
+      t1 += ror32(t2,17) ^ ror32(t2,19) ^ (t2>>10);
+      t2 = buffer.w[(i-15)&15];
+      t1 += ror32(t2,7) ^ ror32(t2,18) ^ (t2>>3);
+      buffer.w[i&15] = t1;
+    }
+    t1 = h;
+    t1 += ror32(e,6) ^ ror32(e,11) ^ ror32(e,25); // ∑1(e)
+    t1 += g ^ (e & (g ^ f)); // Ch(e,f,g)
+    t1 += pgm_read_dword(sha256K+i); // Ki
+    t1 += buffer.w[i&15]; // Wi
+    t2 = ror32(a,2) ^ ror32(a,13) ^ ror32(a,22); // ∑0(a)
+    t2 += ((b & c) | (a & (b | c))); // Maj(a,b,c)
+    h=g; g=f; f=e; e=d+t1; d=c; c=b; b=a; a=t1+t2;
+  }
+  state.w[0] += a;
+  state.w[1] += b;
+  state.w[2] += c;
+  state.w[3] += d;
+  state.w[4] += e;
+  state.w[5] += f;
+  state.w[6] += g;
+  state.w[7] += h;
+}
+
+void Sha256Class::addUncounted(uint8_t data) {
+  buffer.b[bufferOffset ^ 3] = data;
+  bufferOffset++;
+  if (bufferOffset == BUFFER_SIZE) {
+    hashBlock();
+    bufferOffset = 0;
+  }
+}
+
+void Sha256Class::write(uint8_t data) {
+  ++byteCount;
+  addUncounted(data);
+}
+
+void Sha256Class::pad() {
+  // Implement SHA-256 padding (fips180-2 §5.1.1)
+
+  // Pad with 0x80 followed by 0x00 until the end of the block
+  addUncounted(0x80);
+  while (bufferOffset != 56) addUncounted(0x00);
+
+  // Append length in the last 8 bytes
+  addUncounted(0); // We're only using 32 bit lengths
+  addUncounted(0); // But SHA-1 supports 64 bit lengths
+  addUncounted(0); // So zero pad the top bits
+  addUncounted(byteCount >> 29); // Shifting to multiply by 8
+  addUncounted(byteCount >> 21); // as SHA-1 supports bitstreams as well as
+  addUncounted(byteCount >> 13); // byte.
+  addUncounted(byteCount >> 5);
+  addUncounted(byteCount << 3);
+}
+
+
+uint8_t* Sha256Class::result(void) {
+  // Pad to complete the last block
+  pad();
+  
+  // Swap byte order back
+  for (int i=0; i<8; i++) {
+    uint32_t a,b;
+    a=state.w[i];
+    b=a<<24;
+    b|=(a<<8) & 0x00ff0000;
+    b|=(a>>8) & 0x0000ff00;
+    b|=a>>24;
+    state.w[i]=b;
+  }
+  
+  // Return pointer to hash (20 characters)
+  return state.b;
+}
+
+#define HMAC_IPAD 0x36
+#define HMAC_OPAD 0x5c
+
+uint8_t keyBuffer[BLOCK_LENGTH]; // K0 in FIPS-198a
+uint8_t innerHash[HASH_LENGTH];
+
+void Sha256Class::initHmac(const uint8_t* key, int keyLength) {
+  uint8_t i;
+  memset(keyBuffer,0,BLOCK_LENGTH);
+  if (keyLength > BLOCK_LENGTH) {
+    // Hash long keys
+    init();
+    for (;keyLength--;) write(*key++);
+    memcpy(keyBuffer,result(),HASH_LENGTH);
+  } else {
+    // Block length keys are used as is
+    memcpy(keyBuffer,key,keyLength);
+  }
+  // Start inner hash
+  init();
+  for (i=0; i<BLOCK_LENGTH; i++) {
+    write(keyBuffer[i] ^ HMAC_IPAD);
+  }
+}
+
+uint8_t* Sha256Class::resultHmac(void) {
+  uint8_t i;
+  // Complete inner hash
+  memcpy(innerHash,result(),HASH_LENGTH);
+  // Calculate outer hash
+  init();
+  for (i=0; i<BLOCK_LENGTH; i++) write(keyBuffer[i] ^ HMAC_OPAD);
+  for (i=0; i<HASH_LENGTH; i++) write(innerHash[i]);
+  return result();
+}
diff --git a/libraries/MySensors/utility/sha256.h b/libraries/MySensors/utility/sha256.h
new file mode 100644
index 0000000..022b11e
--- /dev/null
+++ b/libraries/MySensors/utility/sha256.h
@@ -0,0 +1,40 @@
+// This code is taken from https://github.com/Cathedrow/Cryptosuite (Peter Knight) and is lightly modified for MySensors use
+#ifndef Sha256_h
+#define Sha256_h
+
+#include <inttypes.h>
+
+#define HASH_LENGTH 32
+#define BLOCK_LENGTH 64
+
+union _buffer {
+  uint8_t b[BLOCK_LENGTH];
+  uint32_t w[BLOCK_LENGTH/4];
+};
+union _state {
+  uint8_t b[HASH_LENGTH];
+  uint32_t w[HASH_LENGTH/4];
+};
+
+class Sha256Class
+{
+  public:
+    void init(void);
+    void initHmac(const uint8_t* secret, int secretLength);
+    uint8_t* result(void);
+    uint8_t* resultHmac(void);
+    virtual void write(uint8_t);
+  private:
+    void pad();
+    void addUncounted(uint8_t data);
+    void hashBlock();
+    uint32_t ror32(uint32_t number, uint8_t bits);
+    _buffer buffer;
+    uint8_t bufferOffset;
+    _state state;
+    uint32_t byteCount;
+    uint8_t keyBuffer[BLOCK_LENGTH];
+    uint8_t innerHash[HASH_LENGTH];
+};
+
+#endif