@Override
  public EncryptedKeyset readEncrypted() throws IOException {
    return EncryptedKeyset.parseFrom(readPref(), ExtensionRegistryLite.getEmptyRegistry());
  }
Creates a {@link KeysetReader} that reads and hex-decodes keysets from the preference
name {@code keysetName} in the private shared preferences file {@code prefFilename}.

<p>If {@code prefFilename} is null, uses the default shared preferences file.

@throws IOException if cannot read the keyset
@throws IllegalArgumentException if {@code keysetName} is null
java_src/src/main/java/com/google/crypto/tink/integration/android/SharedPrefKeysetReader.java