static SECPPrivateKey loadPrivateKey(final File file) {
    try {
      final List<String> info = Files.readAllLines(file.toPath());
      if (info.size() != 1) {
        throw new IllegalArgumentException("Supplied file does not contain valid keyPair pair.");
      }
      return SIGNATURE_ALGORITHM.get().createPrivateKey(Bytes32.fromHexString((info.get(0))));
    } catch (IOException ex) {
      throw new IllegalArgumentException("Supplied file does not contain valid keyPair pair.");
    }
  }
Load secp private key.

@param file the file
@return the secp private key
crypto/algorithms/src/main/java/org/hyperledger/besu/crypto/KeyPairUtil.java