private static EllipticCurveType getCurveType(PemKeyType pemKeyType) {
    switch (pemKeyType.keySizeInBits) {
      case 256:
        return EllipticCurveType.NIST_P256;
      case 384:
        return EllipticCurveType.NIST_P384;
      case 521:
        return EllipticCurveType.NIST_P521;
      default:
        break;
    }
    throw new IllegalArgumentException(
        "unsupported curve for key size: " + pemKeyType.keySizeInBits);
  }
Reads a single PEM key from {@code reader}. Invalid or unparsable PEM would be ignored
java_src/src/main/java/com/google/crypto/tink/signature/SignaturePemKeysetReader.java