SHA256 bug fix - end command only accepts 63 bytes

-the END command of an SHA calculation cannot accept more than 63 bytes. (Datasheet Page 83) .

Previously, this function, sha256(), was sending the last chunk (all 64 bytes) with the end command, and so it was failing when you sent any message data that was exactly divisable by the block size (i.e. 64, 128,256, and so on).

Author: Pete Lewis

keywords.txt

@@ -30,6 +30,7 @@ lockDataSlot0						KEYWORD2
 generatePublicKey						KEYWORD2
 createSignature						KEYWORD2
 verifySignature						KEYWORD2
+sha256						KEYWORD2
 
 
 #######################################

src/SparkFun_ATECCX08a_Arduino_Library.cpp

@@ -975,8 +975,11 @@ boolean ATECCX08A::verifySignature(uint8_t *message, uint8_t *signature, uint8_t
 boolean ATECCX08A::sha256(uint8_t * plain, size_t len, uint8_t * hash)
 {
 	int i;
-	int j;
 	size_t chunks = len / SHA_BLOCK_SIZE + !!(len % SHA_BLOCK_SIZE);
+  if((len % SHA_BLOCK_SIZE) == 0) chunks += 1; // END command can only accept up to 63 bytes, so we must add a "blank chunk" for the end command
+
+  // Serial.print("chunks:");
+  // Serial.println(chunks);
 
 	if (!sendCommand(COMMAND_OPCODE_SHA, SHA_START, 0))
 		return false;
@@ -1001,9 +1004,16 @@ boolean ATECCX08A::sha256(uint8_t * plain, size_t len, uint8_t * hash)
 		if (inputBuffer[RESPONSE_SIGNAL_INDEX] != ATRCC508A_SUCCESSFUL_SHA)
 			return false;
 
-		if ((len % SHA_BLOCK_SIZE) && (i + 1 == chunks))
+		if (i + 1 == chunks) // if we're on the last chunk, there will be a remainder or 0 (and 0 is okay for an end command)
 			data_size = len % SHA_BLOCK_SIZE;
 
+    // Serial.print("chunk:");
+    // Serial.println(i);
+    // Serial.print("data_size:");
+    // Serial.println(data_size);
+    // Serial.print("update vs end:");
+    // Serial.println((i + 1 != chunks) ? SHA_UPDATE : SHA_END);
+
 		/* Send next */
 		if (!sendCommand(COMMAND_OPCODE_SHA, (i + 1 != chunks) ? SHA_UPDATE : SHA_END, data_size, plain + i * SHA_BLOCK_SIZE, data_size))
 			return false;