Update example

src/examples/ecc_raw_private_key.cpp

@@ -14,13 +14,23 @@ int main() {
       Botan::hex_decode_locked("D2AC61C35CAEE918E47B0BD5E61DA9B3A5C2964AB317647DEF6DFC042A06C829");
 
    const auto domain = Botan::EC_Group::from_name(curve_name);
-   const auto private_scalar = Botan::BigInt(private_scalar_bytes);
+
+   // This function will return nullopt if the value is not in the valid range
+   // for the group. Note this includes the case where the bytestring is not
+   // exactly of length equal to the group order, here 32 bytes.
+   const auto private_scalar = Botan::EC_Scalar::deserialize(domain, private_scalar_bytes);
+
+   if(!private_scalar) {
+      std::cerr << "Private key is invalid\n";
+      return 1;
+   }
 
    // This loads the private scalar into an ECDH_PrivateKey. Creating an
    // ECDSA_PrivateKey would work the same way.
-   const auto private_key = Botan::ECDH_PrivateKey(domain, private_scalar);
+   const auto private_key = Botan::ECDH_PrivateKey(domain, private_scalar.value());
    const auto public_key = private_key.public_key();
 
    std::cout << "Private Key (PEM):\n\n" << Botan::PKCS8::PEM_encode(private_key) << '\n';
    std::cout << "Public Key (PEM):\n\n" << Botan::X509::PEM_encode(*public_key) << '\n';
+   return 0;
 }