Add function to compare certificate signature

Author: pennam

src/utility/SElementArduinoCloudCertificate.cpp

@@ -126,6 +126,25 @@ int SElementArduinoCloudCertificate::read(SecureElement & se, ECP256Certificate
   return 1;
 }
 
+int SElementArduinoCloudCertificate::signatureCompare(const byte * signatureA, const String & signatureB)
+{
+  byte signatureBytes[ECP256_CERT_SIGNATURE_LENGTH];
+
+  if (signatureB.length() == 0 || signatureA == nullptr) {
+    DEBUG_ERROR("SEACC::%s input params error.", __FUNCTION__);
+    return -1;
+  }
+
+  hexStringToBytes(signatureB, signatureBytes, sizeof(signatureBytes));
+
+  /* If authorityKeyId are matching there is no need to rebuild*/
+  if (memcmp(signatureBytes, signatureA , sizeof(signatureBytes)) == 0) {
+    DEBUG_VERBOSE("SEACC::%s signatures are equal", __FUNCTION__);
+    return 0;
+  }
+  return 1;
+}
+
 int SElementArduinoCloudCertificate::isAuthorityKeyIdDifferent(const ECP256Certificate & cert, const String & authorityKeyIdentifier)
 {
   byte authorityKeyIdentifierBytes[ECP256_CERT_AUTHORITY_KEY_ID_LENGTH];

src/utility/SElementArduinoCloudCertificate.h

@@ -29,6 +29,7 @@ class SElementArduinoCloudCertificate : public SElementCertificate
   static int write(SecureElement & se, ECP256Certificate & cert, const SElementArduinoCloudSlot certSlot);
   static int read(SecureElement & se, ECP256Certificate & cert, const SElementArduinoCloudSlot certSlot, const SElementArduinoCloudSlot keySlot = SElementArduinoCloudSlot::Key);
   static int isAuthorityKeyIdDifferent(const ECP256Certificate & cert, const String & authorityKeyIdentifier);
+  static int signatureCompare(const byte * signatureA, const String & signatureB);
   static int rebuild(SecureElement & se, ECP256Certificate & cert, const String & deviceId,
                     const String & notBefore, const String & notAfter, const String & serialNumber,
                     const String & authorityKeyIdentifier, const String & signature,