fix: input length for ECCX08.ecSign() is 32 bytes

When using ECCX08.ecSign() the input buffer should
be exactly 32 bytes long. The old example worked
only because the signature was generated and then
checked on the first 32 bytes of the 64 bytes buffer.

examples/ECCX08Signing/ECCX08Signing.ino

@@ -6,7 +6,7 @@
   is printed to the Serial Monitor. Then the signature is
   verified using the public key of the slot.
 
-  NOTE: the input data must be 64 bytes in length!
+  NOTE: the input data must be 32 bytes in length!
 
   Circuit:
    - MKR board with ECC508 or ECC608 on board
@@ -17,11 +17,9 @@
 
 #include <ArduinoECCX08.h>
 
-const byte input[64] = {
+const byte input[32] = {
   0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
-  0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f,
-  0x20, 0x21, 0x22, 0x23, 0x24, 0x25, 0x26, 0x27, 0x28, 0x29, 0x2a, 0x2b, 0x2c, 0x2d, 0x2e, 0x2f,
-  0x30, 0x31, 0x32, 0x33, 0x34, 0x35, 0x36, 0x37, 0x38, 0x39, 0x3a, 0x3b, 0x3c, 0x3d, 0x3e, 0x3f
+  0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17, 0x18, 0x19, 0x1a, 0x1b, 0x1c, 0x1d, 0x1e, 0x1f
 };
 
 const int slot = 0;
@@ -57,7 +55,7 @@ void setup() {
   Serial.print(" is:   ");
   printBufferHex(publicKey, sizeof(publicKey));
 
-  // calculate the signature, input MUST be 64-byte array
+  // calculate the signature, input MUST be 32-byte array
   byte signature[64];
   ECCX08.ecSign(slot, input, signature);