@Override
  public boolean hasSecret() {
    return hasSecret;
  }
Constructs a ProtoKey with {@code hasSecret()} returning true if the input {@code KeyData} has
key material of type UNKNOWN_KEYMATERIAL, SYMMETRIC, or ASYMMETRIC_PRIVATE.
java_src/src/main/java/com/google/crypto/tink/tinkkey/internal/ProtoKey.java