implementing methods from SecureElement library

Making ECCX08 compatible with abstract SecureElement usage from
Arduino_SecureElement library

Author: andreagilardoni

src/ECCX08.cpp

@@ -73,8 +73,12 @@ void ECCX08Class::end()
 #endif
 }
 
-int ECCX08Class::serialNumber(byte sn[])
+int ECCX08Class::serialNumber(byte sn[], size_t len)
 {
+  if(len < 12) {
+    return 0;
+  }
+
   if (!read(0, 0, &sn[0], 4)) {
     return 0;
   }
@@ -252,6 +256,18 @@ int ECCX08Class::ecSign(int slot, const byte message[], byte signature[])
   return 1;
 }
 
+int ECCX08Class::SHA256(const uint8_t *buffer, size_t size, uint8_t *digest)
+{
+  beginSHA256();
+  uint8_t * cursor = (uint8_t*)buffer;
+  uint32_t bytes_read = 0;
+
+  for(; bytes_read + 64 < size; bytes_read += 64, cursor += 64) {
+    updateSHA256(cursor);
+  }
+  return endSHA256(cursor, size - bytes_read, digest);
+}
+
 int ECCX08Class::beginSHA256()
 {
   uint8_t status;

src/ECCX08.h

@@ -33,7 +33,7 @@ class ECCX08Class
   int begin(uint8_t i2cAddress);
   void end();
 
-  int serialNumber(byte sn[]);
+  int serialNumber(byte sn[], size_t length=12);
   String serialNumber();
 
   long random(long max);
@@ -46,6 +46,7 @@ class ECCX08Class
   int ecdsaVerify(const byte message[], const byte signature[], const byte pubkey[]);
   int ecSign(int slot, const byte message[], byte signature[]);
 
+  int SHA256(const uint8_t *buffer, size_t size, uint8_t *digest);
   int beginSHA256();
   int updateSHA256(const byte data[]); // 64 bytes
   int endSHA256(byte result[]);
@@ -55,7 +56,7 @@ class ECCX08Class
   int writeSlot(int slot, const byte data[], int length);
 
   int locked();
-  int writeConfiguration(const byte data[]);
+  int writeConfiguration(const byte data[]=ECCX08_DEFAULT_TLS_CONFIG);
   int readConfiguration(byte data[]);
   int lock();