message: Use ReadSecretBytesFromStream in derivation.
diff: #include "tink/subtle/subtle_util_boringssl.h"
  #include "tink/util/enums.h"
  #include "tink/util/errors.h"
  +#include "tink/util/input_stream_util.h"
  #include "tink/util/protobuf_helper.h"
  #include "tink/util/secret_data.h"
  #include "tink/util/status.h"
  @@ -83,8 +84,8 @@ StatusOr<Ed25519PrivateKey> Ed25519SignKeyManager::DeriveKey(
  ValidateVersion(key_format.version(), get_version());
  if (!status.ok()) return status;
  - crypto::tink::util::StatusOr<std::string> randomness =
  - ReadBytesFromStream(kEd25519SecretSeedSize, input_stream);
  + crypto::tink::util::StatusOr<util::SecretData> randomness =
  + ReadSecretBytesFromStream(kEd25519SecretSeedSize, input_stream);
  if (!randomness.ok()) {
  if (randomness.status().error_code() == util::error::OUT_OF_RANGE) {
  return crypto::tink::util::Status(
  @@ -94,7 +95,7 @@ StatusOr<Ed25519PrivateKey> Ed25519SignKeyManager::DeriveKey(
  return randomness.status();
  }
  auto key = subtle::SubtleUtilBoringSSL::GetNewEd25519KeyFromSeed(
  - util::SecretDataFromStringView(randomness.ValueOrDie()));
  + randomness.ValueOrDie());
  Ed25519PrivateKey ed25519_private_key;
  ed25519_private_key.set_version(get_version());
  