Use `ctype = STRING_PIECE` on all `key_value`s

PiperOrigin-RevId: 633521257
Change-Id: I2754393df8663b0d9cecdd0b797365c8c32bfbcf

43 files changed, 73 insertions, 53 deletions

diff --git a/proto/aes_cmac.proto b/proto/aes_cmac.proto
index d1de8e3d9..b5dbd941e 100644
--- a/proto/aes_cmac.proto
+++ b/proto/aes_cmac.proto
@@ -29,7 +29,7 @@ message AesCmacParams {
 // key_type: type.googleapis.com/google.crypto.tink.AesCmacKey
 message AesCmacKey {
   uint32 version = 1;
-  bytes key_value = 2;
+  bytes key_value = 2;  // Placeholder for ctype.
   AesCmacParams params = 3;
 }
 
diff --git a/proto/aes_cmac_prf.proto b/proto/aes_cmac_prf.proto
index dd8dcae1e..94fe509d4 100644
--- a/proto/aes_cmac_prf.proto
+++ b/proto/aes_cmac_prf.proto
@@ -25,7 +25,7 @@ option go_package = "github.com/tink-crypto/tink-go/v2/proto/aes_cmac_prf_go_pro
 // key_type: type.googleapis.com/google.crypto.tink.AesCmacPrfKey
 message AesCmacPrfKey {
   uint32 version = 1;
-  bytes key_value = 2;
+  bytes key_value = 2;  // Placeholder for ctype.
 }
 
 message AesCmacPrfKeyFormat {
diff --git a/proto/aes_ctr.proto b/proto/aes_ctr.proto
index a873097c7..66c0ca1e5 100644
--- a/proto/aes_ctr.proto
+++ b/proto/aes_ctr.proto
@@ -35,5 +35,5 @@ message AesCtrKeyFormat {
 message AesCtrKey {
   uint32 version = 1;
   AesCtrParams params = 2;
-  bytes key_value = 3;
+  bytes key_value = 3;  // Placeholder for ctype.
 }
diff --git a/proto/aes_ctr_hmac_streaming.proto b/proto/aes_ctr_hmac_streaming.proto
index 599e267d6..7927bde81 100644
--- a/proto/aes_ctr_hmac_streaming.proto
+++ b/proto/aes_ctr_hmac_streaming.proto
@@ -42,5 +42,5 @@ message AesCtrHmacStreamingKeyFormat {
 message AesCtrHmacStreamingKey {
   uint32 version = 1;
   AesCtrHmacStreamingParams params = 2;
-  bytes key_value = 3;  // the main key, aka. "ikm", input key material
+  bytes key_value = 3;  // Placeholder for ctype.  // the main key, aka. "ikm", input key material
 }
diff --git a/proto/aes_gcm.proto b/proto/aes_gcm.proto
index 1908c4ae0..3724b0a13 100644
--- a/proto/aes_gcm.proto
+++ b/proto/aes_gcm.proto
@@ -63,5 +63,5 @@ message AesGcmKeyFormat {
 
 message AesGcmKey {
   uint32 version = 1;
-  bytes key_value = 3;
+  bytes key_value = 3;  // Placeholder for ctype.
 }
diff --git a/proto/aes_gcm_hkdf_streaming.proto b/proto/aes_gcm_hkdf_streaming.proto
index a436abbe9..c5e40236b 100644
--- a/proto/aes_gcm_hkdf_streaming.proto
+++ b/proto/aes_gcm_hkdf_streaming.proto
@@ -42,5 +42,5 @@ message AesGcmHkdfStreamingKeyFormat {
 message AesGcmHkdfStreamingKey {
   uint32 version = 1;
   AesGcmHkdfStreamingParams params = 2;
-  bytes key_value = 3;
+  bytes key_value = 3;  // Placeholder for ctype.
 }
diff --git a/proto/aes_gcm_siv.proto b/proto/aes_gcm_siv.proto
index c663aee60..fee87d760 100644
--- a/proto/aes_gcm_siv.proto
+++ b/proto/aes_gcm_siv.proto
@@ -32,5 +32,5 @@ message AesGcmSivKeyFormat {
 // key_type: type.googleapis.com/google.crypto.tink.AesGcmSivKey
 message AesGcmSivKey {
   uint32 version = 1;
-  bytes key_value = 3;
+  bytes key_value = 3;  // Placeholder for ctype.
 }
diff --git a/proto/aes_siv.proto b/proto/aes_siv.proto
index 0f605eae7..2c5e013e3 100644
--- a/proto/aes_siv.proto
+++ b/proto/aes_siv.proto
@@ -40,5 +40,5 @@ message AesSivKeyFormat {
 message AesSivKey {
   uint32 version = 1;
   // First half is AES-CTR key, second is AES-SIV.
-  bytes key_value = 2;
+  bytes key_value = 2;  // Placeholder for ctype.
 }
diff --git a/proto/chacha20_poly1305.proto b/proto/chacha20_poly1305.proto
index 86f8545c4..8f26821c5 100644
--- a/proto/chacha20_poly1305.proto
+++ b/proto/chacha20_poly1305.proto
@@ -29,5 +29,5 @@ message ChaCha20Poly1305KeyFormat {}
 // at https://tools.ietf.org/html/rfc7539#section-2.8.
 message ChaCha20Poly1305Key {
   uint32 version = 1;
-  bytes key_value = 2;
+  bytes key_value = 2;  // Placeholder for ctype.
 }
diff --git a/proto/ecdsa.proto b/proto/ecdsa.proto
index 89dfebb5e..e89783e8a 100644
--- a/proto/ecdsa.proto
+++ b/proto/ecdsa.proto
@@ -74,7 +74,7 @@ message EcdsaPrivateKey {
   EcdsaPublicKey public_key = 2;
   // Unsigned big integer in bigendian representation.
   // Required.
-  bytes key_value = 3;
+  bytes key_value = 3;  // Placeholder for ctype.
 }
 
 message EcdsaKeyFormat {
diff --git a/proto/ecies_aead_hkdf.proto b/proto/ecies_aead_hkdf.proto
index 488b2f059..fa7eca5fd 100644
--- a/proto/ecies_aead_hkdf.proto
+++ b/proto/ecies_aead_hkdf.proto
@@ -105,7 +105,7 @@ message EciesAeadHkdfPrivateKey {
   EciesAeadHkdfPublicKey public_key = 2;
 
   // Required.
-  bytes key_value = 3;  // Big integer in bigendian representation.
+  bytes key_value = 3;  // Placeholder for ctype.  // Big integer in bigendian representation.
 }
 
 message EciesAeadHkdfKeyFormat {
diff --git a/proto/ed25519.proto b/proto/ed25519.proto
index 763db39f8..8d6234a92 100644
--- a/proto/ed25519.proto
+++ b/proto/ed25519.proto
@@ -36,7 +36,7 @@ message Ed25519PublicKey {
   // The public key is 32 bytes, encoded according to
   // https://tools.ietf.org/html/rfc8032#section-5.1.2.
   // Required.
-  bytes key_value = 2;
+  bytes key_value = 2;  // Placeholder for ctype.
 }
 
 // key_type: type.googleapis.com/google.crypto.tink.Ed25519PrivateKey
@@ -46,7 +46,7 @@ message Ed25519PrivateKey {
   // The private key is 32 bytes of cryptographically secure random data.
   // See https://tools.ietf.org/html/rfc8032#section-5.1.5.
   // Required.
-  bytes key_value = 2;
+  bytes key_value = 2;  // Placeholder for ctype.
   // The corresponding public key.
   Ed25519PublicKey public_key = 3;
 }
diff --git a/proto/experimental/pqcrypto/dilithium.proto b/proto/experimental/pqcrypto/dilithium.proto
index fa4c05bb3..48e477b66 100644
--- a/proto/experimental/pqcrypto/dilithium.proto
+++ b/proto/experimental/pqcrypto/dilithium.proto
@@ -43,7 +43,7 @@ message DilithiumPublicKey {
   // Required.
   uint32 version = 1;
   // Required.
-  bytes key_value = 2;
+  bytes key_value = 2;  // Placeholder for ctype.
   // Required
   DilithiumParams params = 3;
 }
@@ -53,7 +53,7 @@ message DilithiumPrivateKey {
   // Required.
   uint32 version = 1;
   // Required.
-  bytes key_value = 2;
+  bytes key_value = 2;  // Placeholder for ctype.
   // The corresponding public key.
   DilithiumPublicKey public_key = 3;
 }
diff --git a/proto/experimental/pqcrypto/falcon.proto b/proto/experimental/pqcrypto/falcon.proto
index 13103bc1f..b71a56b1c 100644
--- a/proto/experimental/pqcrypto/falcon.proto
+++ b/proto/experimental/pqcrypto/falcon.proto
@@ -30,7 +30,7 @@ message FalconPublicKey {
   // Required.
   uint32 version = 1;
   // Required.
-  bytes key_value = 2;
+  bytes key_value = 2;  // Placeholder for ctype.
 }
 
 // key_type: type.googleapis.com/google.crypto.tink.FalconPrivateKey
@@ -38,7 +38,7 @@ message FalconPrivateKey {
   // Required.
   uint32 version = 1;
   // Required.
-  bytes key_value = 2;
+  bytes key_value = 2;  // Placeholder for ctype.
   // The corresponding public key.
   FalconPublicKey public_key = 3;
 }
diff --git a/proto/experimental/pqcrypto/slh_dsa.proto b/proto/experimental/pqcrypto/slh_dsa.proto
index b3768c64c..120205efb 100644
--- a/proto/experimental/pqcrypto/slh_dsa.proto
+++ b/proto/experimental/pqcrypto/slh_dsa.proto
@@ -51,7 +51,7 @@ message SlhDsaPublicKey {
   // Required.
   uint32 version = 1;
   // Required.
-  bytes key_value = 2;
+  bytes key_value = 2;  // Placeholder for ctype.
   // Required
   SlhDsaParams params = 3;
 }
@@ -61,7 +61,7 @@ message SlhDsaPrivateKey {
   // Required.
   uint32 version = 1;
   // Required.
-  bytes key_value = 2;
+  bytes key_value = 2;  // Placeholder for ctype.
   // Required. The corresponding public key.
   SlhDsaPublicKey public_key = 3;
 }
diff --git a/proto/experimental/pqcrypto/sphincs.proto b/proto/experimental/pqcrypto/sphincs.proto
index 381451cdc..169ff4b61 100644
--- a/proto/experimental/pqcrypto/sphincs.proto
+++ b/proto/experimental/pqcrypto/sphincs.proto
@@ -59,7 +59,7 @@ message SphincsPublicKey {
   // Required.
   uint32 version = 1;
   // Required.
-  bytes key_value = 2;
+  bytes key_value = 2;  // Placeholder for ctype.
   // Required
   SphincsParams params = 3;
 }
@@ -69,7 +69,7 @@ message SphincsPrivateKey {
   // Required.
   uint32 version = 1;
   // Required.
-  bytes key_value = 2;
+  bytes key_value = 2;  // Placeholder for ctype.
   // The corresponding public key.
   SphincsPublicKey public_key = 3;
 }
diff --git a/proto/hkdf_prf.proto b/proto/hkdf_prf.proto
index e2c4f4e00..3b98d06eb 100644
--- a/proto/hkdf_prf.proto
+++ b/proto/hkdf_prf.proto
@@ -38,7 +38,7 @@ message HkdfPrfParams {
 message HkdfPrfKey {
   uint32 version = 1;
   HkdfPrfParams params = 2;
-  bytes key_value = 3;
+  bytes key_value = 3;  // Placeholder for ctype.
 }
 
 message HkdfPrfKeyFormat {
diff --git a/proto/hmac.proto b/proto/hmac.proto
index 8f0f9e509..bd268f099 100644
--- a/proto/hmac.proto
+++ b/proto/hmac.proto
@@ -33,7 +33,7 @@ message HmacParams {
 message HmacKey {
   uint32 version = 1;
   HmacParams params = 2;
-  bytes key_value = 3;
+  bytes key_value = 3;  // Placeholder for ctype.
 }
 
 message HmacKeyFormat {
diff --git a/proto/hmac_prf.proto b/proto/hmac_prf.proto
index 533895128..159d3db57 100644
--- a/proto/hmac_prf.proto
+++ b/proto/hmac_prf.proto
@@ -32,7 +32,7 @@ message HmacPrfParams {
 message HmacPrfKey {
   uint32 version = 1;
   HmacPrfParams params = 2;
-  bytes key_value = 3;
+  bytes key_value = 3;  // Placeholder for ctype.
 }
 
 message HmacPrfKeyFormat {
diff --git a/proto/jwt_ecdsa.proto b/proto/jwt_ecdsa.proto
index 25b6980fd..e8f1be24b 100644
--- a/proto/jwt_ecdsa.proto
+++ b/proto/jwt_ecdsa.proto
@@ -52,7 +52,7 @@ message JwtEcdsaPrivateKey {
   uint32 version = 1;
   JwtEcdsaPublicKey public_key = 2;
   // Unsigned big integer in bigendian representation.
-  bytes key_value = 3;
+  bytes key_value = 3;  // Placeholder for ctype.
 }
 
 message JwtEcdsaKeyFormat {
diff --git a/proto/jwt_hmac.proto b/proto/jwt_hmac.proto
index 00530023c..c62932300 100644
--- a/proto/jwt_hmac.proto
+++ b/proto/jwt_hmac.proto
@@ -34,7 +34,7 @@ enum JwtHmacAlgorithm {
 message JwtHmacKey {
   uint32 version = 1;
   JwtHmacAlgorithm algorithm = 2;
-  bytes key_value = 3;
+  bytes key_value = 3;  // Placeholder for ctype.
 
   // Optional, custom kid header value to be used with "RAW" keys.
   // "TINK" keys with this value set will be rejected.
diff --git a/proto/xchacha20_poly1305.proto b/proto/xchacha20_poly1305.proto
index 530e57383..d080b7790 100644
--- a/proto/xchacha20_poly1305.proto
+++ b/proto/xchacha20_poly1305.proto
@@ -29,5 +29,5 @@ message XChaCha20Poly1305KeyFormat {
 // key_type: type.googleapis.com/google.crypto.tink.XChaCha20Poly1305Key
 message XChaCha20Poly1305Key {
   uint32 version = 1;
-  bytes key_value = 3;
+  bytes key_value = 3;  // Placeholder for ctype.
 }
diff --git a/tink/BUILD.bazel b/tink/BUILD.bazel
index 185e31395..81613a264 100644
--- a/tink/BUILD.bazel
+++ b/tink/BUILD.bazel
@@ -1097,6 +1097,7 @@ cc_test(
         "//tink/util:validation",
         "@com_google_absl//absl/memory",
         "@com_google_absl//absl/status",
+        "@com_google_absl//absl/strings:string_view",
         "@com_google_googletest//:gtest_main",
     ],
 )
@@ -1118,6 +1119,7 @@ cc_test(
         "//tink/util:test_util",
         "//tink/util:validation",
         "@com_google_absl//absl/status",
+        "@com_google_absl//absl/strings:string_view",
         "@com_google_googletest//:gtest_main",
     ],
 )
diff --git a/tink/CMakeLists.txt b/tink/CMakeLists.txt
index 4c3565a7c..faa986529 100644
--- a/tink/CMakeLists.txt
+++ b/tink/CMakeLists.txt
@@ -1034,6 +1034,7 @@ tink_cc_test(
     gmock
     absl::memory
     absl::status
+    absl::string_view
     tink::subtle::subtle
     tink::util::secret_data
     tink::util::status
@@ -1052,6 +1053,7 @@ tink_cc_test(
     tink::core::key_manager_impl
     gmock
     absl::status
+    absl::string_view
     tink::subtle::subtle
     tink::util::input_stream_util
     tink::util::istream_input_stream
diff --git a/tink/config/BUILD.bazel b/tink/config/BUILD.bazel
index 037bda87a..447798cc5 100644
--- a/tink/config/BUILD.bazel
+++ b/tink/config/BUILD.bazel
@@ -233,6 +233,7 @@ cc_test(
         "//tink/util:test_matchers",
         "@com_google_absl//absl/memory",
         "@com_google_absl//absl/status",
+        "@com_google_absl//absl/strings:string_view",
         "@com_google_googletest//:gtest_main",
     ],
 )
diff --git a/tink/config/CMakeLists.txt b/tink/config/CMakeLists.txt
index ae975255c..71cb7e31e 100644
--- a/tink/config/CMakeLists.txt
+++ b/tink/config/CMakeLists.txt
@@ -207,6 +207,7 @@ tink_cc_test(
     gmock
     absl::memory
     absl::status
+    absl::string_view
     tink::core::key_type_manager
     tink::core::template_util
     tink::core::input_stream
diff --git a/tink/config/global_registry_test.cc b/tink/config/global_registry_test.cc
index 38d94d79c..e483e062b 100644
--- a/tink/config/global_registry_test.cc
+++ b/tink/config/global_registry_test.cc
@@ -24,6 +24,7 @@
 #include "gtest/gtest.h"
 #include "absl/memory/memory.h"
 #include "absl/status/status.h"
+#include "absl/strings/string_view.h"
 #include "tink/core/key_type_manager.h"
 #include "tink/core/template_util.h"
 #include "tink/input_stream.h"
@@ -51,7 +52,7 @@ using ::google::crypto::tink::OutputPrefixType;
 
 class FakePrimitive {
  public:
-  explicit FakePrimitive(std::string s) : s_(s) {}
+  explicit FakePrimitive(absl::string_view s) : s_(s) {}
   std::string get() { return s_; }
 
  private:
diff --git a/tink/core/key_manager_impl_test.cc b/tink/core/key_manager_impl_test.cc
index 7497e5737..32802cf1e 100644
--- a/tink/core/key_manager_impl_test.cc
+++ b/tink/core/key_manager_impl_test.cc
@@ -23,6 +23,7 @@
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
 #include "absl/status/status.h"
+#include "absl/strings/string_view.h"
 #include "tink/aead.h"
 #include "tink/subtle/aes_gcm_boringssl.h"
 #include "tink/subtle/random.h"
@@ -57,7 +58,7 @@ using ::testing::SizeIs;
 // insecure, as it does nothing except provide access to the key.
 class AeadVariant {
  public:
-  explicit AeadVariant(std::string s) : s_(s) {}
+  explicit AeadVariant(absl::string_view s) : s_(s) {}
 
   std::string get() { return s_; }
 
diff --git a/tink/core/key_type_manager_test.cc b/tink/core/key_type_manager_test.cc
index 40f888be1..508bbd3e6 100644
--- a/tink/core/key_type_manager_test.cc
+++ b/tink/core/key_type_manager_test.cc
@@ -24,6 +24,7 @@
 #include "gtest/gtest.h"
 #include "absl/memory/memory.h"
 #include "absl/status/status.h"
+#include "absl/strings/string_view.h"
 #include "tink/aead.h"
 #include "tink/core/template_util.h"
 #include "tink/subtle/aes_gcm_boringssl.h"
@@ -49,7 +50,7 @@ using ::testing::Eq;
 // insecure, as it does nothing except provide access to the key.
 class AeadVariant {
  public:
-  explicit AeadVariant(std::string s) : s_(s) {}
+  explicit AeadVariant(absl::string_view s) : s_(s) {}
 
   std::string get() { return s_; }
 
diff --git a/tink/core/keyset_handle_test.cc b/tink/core/keyset_handle_test.cc
index e43c8b824..b4ba2c7de 100644
--- a/tink/core/keyset_handle_test.cc
+++ b/tink/core/keyset_handle_test.cc
@@ -1052,7 +1052,7 @@ TEST_F(KeysetHandleTest, GetPrimitiveWithConfigFips1402FailsWithNonFipsHandle) {
 
   Keyset keyset;
   AesGcmSivKey key_proto;
-  *key_proto.mutable_key_value() = subtle::Random::GetRandomBytes(16);
+  key_proto.set_key_value(subtle::Random::GetRandomBytes(16));
   test::AddTinkKey(AeadKeyTemplates::Aes256GcmSiv().type_url(), /*key_id=*/13,
                    key_proto, KeyStatusType::ENABLED, KeyData::SYMMETRIC,
                    &keyset);
diff --git a/tink/daead/aes_siv_key_manager_test.cc b/tink/daead/aes_siv_key_manager_test.cc
index fd44271f3..4a41e23fa 100644
--- a/tink/daead/aes_siv_key_manager_test.cc
+++ b/tink/daead/aes_siv_key_manager_test.cc
@@ -167,7 +167,7 @@ TEST(AesSivKeyManagerTest, DeriveKeyWrongVersion) {
 
 TEST(AesSivKeyManagerTest, ValidateKey) {
   AesSivKey key;
-  *key.mutable_key_value() = std::string(64, 'a');
+  key.set_key_value(std::string(64, 'a'));
   key.set_version(0);
   EXPECT_THAT(AesSivKeyManager().ValidateKey(key), IsOk());
 }
@@ -176,18 +176,18 @@ TEST(AesSivKeyManagerTest, ValidateKeyStringLength) {
   AesSivKey key;
     key.set_version(0);
   for (int i = 0 ; i < 64; ++i) {
-    *key.mutable_key_value() = std::string(i, 'a');
+    key.set_key_value(std::string(i, 'a'));
     EXPECT_THAT(AesSivKeyManager().ValidateKey(key), Not(IsOk()));
   }
   for (int i = 65 ; i <= 200; ++i) {
-    *key.mutable_key_value() = std::string(i, 'a');
+    key.set_key_value(std::string(i, 'a'));
     EXPECT_THAT(AesSivKeyManager().ValidateKey(key), Not(IsOk()));
   }
 }
 
 TEST(AesSivKeyManagerTest, ValidateKeyVersion) {
   AesSivKey key;
-  *key.mutable_key_value() = std::string(64, 'a');
+  key.set_key_value(std::string(64, 'a'));
   key.set_version(1);
   EXPECT_THAT(AesSivKeyManager().ValidateKey(key), Not(IsOk()));
 }
diff --git a/tink/experimental/pqcrypto/signature/dilithium_sign_key_manager_test.cc b/tink/experimental/pqcrypto/signature/dilithium_sign_key_manager_test.cc
index 27764a1c4..2e94f60d0 100644
--- a/tink/experimental/pqcrypto/signature/dilithium_sign_key_manager_test.cc
+++ b/tink/experimental/pqcrypto/signature/dilithium_sign_key_manager_test.cc
@@ -161,7 +161,7 @@ TEST_P(DilithiumSignKeyManagerTest, CreateKeyAlwaysNew) {
     StatusOr<DilithiumPrivateKey> private_key =
         DilithiumSignKeyManager().CreateKey(*key_format);
     ASSERT_THAT(private_key, IsOk());
-    keys.insert(private_key->key_value());
+    keys.insert(std::string(private_key->key_value()));
   }
   EXPECT_THAT(keys, SizeIs(num_tests));
 }
diff --git a/tink/experimental/pqcrypto/signature/falcon_sign_key_manager_test.cc b/tink/experimental/pqcrypto/signature/falcon_sign_key_manager_test.cc
index f9683ec84..8a8b22bed 100644
--- a/tink/experimental/pqcrypto/signature/falcon_sign_key_manager_test.cc
+++ b/tink/experimental/pqcrypto/signature/falcon_sign_key_manager_test.cc
@@ -137,7 +137,7 @@ TEST_P(FalconSignKeyManagerTest, CreateKeyAlwaysNew) {
     StatusOr<FalconPrivateKey> private_key =
         FalconSignKeyManager().CreateKey(*key_format);
     ASSERT_THAT(private_key, IsOk());
-    keys.insert(private_key->key_value());
+    keys.insert(std::string(private_key->key_value()));
   }
   EXPECT_THAT(keys, SizeIs(num_tests));
 }
diff --git a/tink/experimental/pqcrypto/signature/sphincs_sign_key_manager_test.cc b/tink/experimental/pqcrypto/signature/sphincs_sign_key_manager_test.cc
index fdc6656e3..4aa0781e8 100644
--- a/tink/experimental/pqcrypto/signature/sphincs_sign_key_manager_test.cc
+++ b/tink/experimental/pqcrypto/signature/sphincs_sign_key_manager_test.cc
@@ -213,7 +213,7 @@ TEST_P(SphincsSignKeyManagerTest, CreateKeyAlwaysNew) {
     StatusOr<SphincsPrivateKey> private_key =
         SphincsSignKeyManager().CreateKey(*key_format);
     ASSERT_THAT(private_key, IsOk());
-    keys.insert(private_key->key_value());
+    keys.insert(std::string(private_key->key_value()));
   }
   EXPECT_THAT(keys, SizeIs(num_tests));
 }
@@ -264,7 +264,8 @@ TEST_P(SphincsSignKeyManagerTest, CreateValid) {
       .private_key_size = test_case.private_key_size};
 
   SphincsPublicKeyPqclean sphincs_public_key_pqclean(
-      private_key->public_key().key_value(), sphincs_params_pqclean);
+      std::string(private_key->public_key().key_value()),
+      sphincs_params_pqclean);
 
   util::StatusOr<std::unique_ptr<PublicKeyVerify>> verifier =
       subtle::SphincsVerify::New(sphincs_public_key_pqclean);
diff --git a/tink/experimental/pqcrypto/signature/sphincs_verify_key_manager.cc b/tink/experimental/pqcrypto/signature/sphincs_verify_key_manager.cc
index 0acf19caf..8e49b84c2 100644
--- a/tink/experimental/pqcrypto/signature/sphincs_verify_key_manager.cc
+++ b/tink/experimental/pqcrypto/signature/sphincs_verify_key_manager.cc
@@ -17,6 +17,7 @@
 #include "tink/experimental/pqcrypto/signature/sphincs_verify_key_manager.h"
 
 #include <memory>
+#include <string>
 
 #include "absl/memory/memory.h"
 #include "absl/strings/str_cat.h"
@@ -55,8 +56,8 @@ SphincsVerifyKeyManager::PublicKeyVerifyFactory::Create(
           EnumsPqcrypto::ProtoToSubtle(public_key.params().sig_length_type()),
       .private_key_size = public_key.params().key_size()};
 
-  SphincsPublicKeyPqclean sphincs_public_key_pqclean(public_key.key_value(),
-                                                     sphincs_params_pqclean);
+  SphincsPublicKeyPqclean sphincs_public_key_pqclean(
+      std::string(public_key.key_value()), sphincs_params_pqclean);
 
   return subtle::SphincsVerify::New(sphincs_public_key_pqclean);
 }
diff --git a/tink/hybrid/internal/hpke_private_key_manager_test.cc b/tink/hybrid/internal/hpke_private_key_manager_test.cc
index 63a6656b3..afdefebd3 100644
--- a/tink/hybrid/internal/hpke_private_key_manager_test.cc
+++ b/tink/hybrid/internal/hpke_private_key_manager_test.cc
@@ -151,7 +151,7 @@ TEST(HpkePrivateKeyManagerTest, CreateP256KeySucceeds) {
     util::StatusOr<HpkePrivateKey> key =
         HpkePrivateKeyManager().CreateKey(key_format);
     ASSERT_THAT(key, IsOk());
-    private_keys.insert(key->private_key());
+    private_keys.insert(std::string(key->private_key()));
     public_keys.insert(key->public_key().public_key());
   }
   EXPECT_THAT(private_keys.size(), Eq(number_of_keys));
@@ -184,7 +184,7 @@ TEST(HpkePrivateKeyManagerTest, CreateP384KeySucceeds) {
     util::StatusOr<HpkePrivateKey> key =
         HpkePrivateKeyManager().CreateKey(key_format);
     ASSERT_THAT(key, IsOk());
-    private_keys.insert(key->private_key());
+    private_keys.insert(std::string(key->private_key()));
     public_keys.insert(key->public_key().public_key());
   }
   EXPECT_THAT(private_keys.size(), Eq(number_of_keys));
@@ -217,7 +217,7 @@ TEST(HpkePrivateKeyManagerTest, CreateP521KeySucceeds) {
     util::StatusOr<HpkePrivateKey> key =
         HpkePrivateKeyManager().CreateKey(key_format);
     ASSERT_THAT(key, IsOk());
-    private_keys.insert(key->private_key());
+    private_keys.insert(std::string(key->private_key()));
     public_keys.insert(key->public_key().public_key());
   }
   EXPECT_THAT(private_keys.size(), Eq(number_of_keys));
diff --git a/tink/internal/BUILD.bazel b/tink/internal/BUILD.bazel
index 8bd8c3c91..9606f5fd7 100644
--- a/tink/internal/BUILD.bazel
+++ b/tink/internal/BUILD.bazel
@@ -1132,6 +1132,7 @@ cc_test(
         "//tink/util:test_util",
         "@com_google_absl//absl/memory",
         "@com_google_absl//absl/status",
+        "@com_google_absl//absl/strings:string_view",
         "@com_google_googletest//:gtest_main",
     ],
 )
@@ -1231,6 +1232,7 @@ cc_test(
         "//tink/util:test_util",
         "@com_google_absl//absl/memory",
         "@com_google_absl//absl/status",
+        "@com_google_absl//absl/strings:string_view",
         "@com_google_googletest//:gtest_main",
     ],
 )
@@ -1277,6 +1279,7 @@ cc_test(
         "//tink/util:test_util",
         "@com_google_absl//absl/memory",
         "@com_google_absl//absl/status",
+        "@com_google_absl//absl/strings:string_view",
         "@com_google_googletest//:gtest_main",
     ],
 )
diff --git a/tink/internal/CMakeLists.txt b/tink/internal/CMakeLists.txt
index 642dffb79..cf4362d14 100644
--- a/tink/internal/CMakeLists.txt
+++ b/tink/internal/CMakeLists.txt
@@ -1062,6 +1062,7 @@ tink_cc_test(
     gmock
     absl::memory
     absl::status
+    absl::string_view
     tink::core::cleartext_keyset_handle
     tink::core::configuration
     tink::core::key_manager_impl
@@ -1167,6 +1168,7 @@ tink_cc_test(
     gmock
     absl::memory
     absl::status
+    absl::string_view
     tink::core::key_type_manager
     tink::core::template_util
     tink::core::input_stream
@@ -1207,6 +1209,7 @@ tink_cc_test(
     gmock
     absl::memory
     absl::status
+    absl::string_view
     tink::core::key_manager_impl
     tink::core::key_type_manager
     tink::core::private_key_type_manager
diff --git a/tink/internal/configuration_impl_test.cc b/tink/internal/configuration_impl_test.cc
index 6bc8d3063..686b44bdf 100644
--- a/tink/internal/configuration_impl_test.cc
+++ b/tink/internal/configuration_impl_test.cc
@@ -24,6 +24,7 @@
 #include "gtest/gtest.h"
 #include "absl/memory/memory.h"
 #include "absl/status/status.h"
+#include "absl/strings/string_view.h"
 #include "tink/cleartext_keyset_handle.h"
 #include "tink/configuration.h"
 #include "tink/core/key_manager_impl.h"
@@ -70,7 +71,7 @@ using ::google::crypto::tink::RsaSsaPssPublicKey;
 
 class FakePrimitive {
  public:
-  explicit FakePrimitive(std::string s) : s_(s) {}
+  explicit FakePrimitive(absl::string_view s) : s_(s) {}
   std::string get() { return s_; }
 
  private:
@@ -79,7 +80,7 @@ class FakePrimitive {
 
 class FakePrimitive2 {
  public:
-  explicit FakePrimitive2(std::string s) : s_(s) {}
+  explicit FakePrimitive2(absl::string_view s) : s_(s) {}
   std::string get() { return s_ + "2"; }
 
  private:
@@ -169,7 +170,7 @@ std::string AddAesGcmKeyToKeyset(Keyset& keyset, uint32_t key_id,
   key_data.set_type_url("type.googleapis.com/google.crypto.tink.AesGcmKey");
   test::AddKeyData(key_data, key_id, output_prefix_type, key_status_type,
                    &keyset);
-  return key.key_value();
+  return std::string(key.key_value());
 }
 
 TEST(ConfigurationImplTest, AddPrimitiveWrapper) {
diff --git a/tink/internal/key_gen_configuration_impl_test.cc b/tink/internal/key_gen_configuration_impl_test.cc
index 6e52e7f88..e4e0996c5 100644
--- a/tink/internal/key_gen_configuration_impl_test.cc
+++ b/tink/internal/key_gen_configuration_impl_test.cc
@@ -24,6 +24,7 @@
 #include "gtest/gtest.h"
 #include "absl/memory/memory.h"
 #include "absl/status/status.h"
+#include "absl/strings/string_view.h"
 #include "tink/aead/aead_key_templates.h"
 #include "tink/core/key_manager_impl.h"
 #include "tink/core/key_type_manager.h"
@@ -62,7 +63,7 @@ using ::google::crypto::tink::RsaSsaPssPublicKey;
 
 class FakePrimitive {
  public:
-  explicit FakePrimitive(std::string s) : s_(s) {}
+  explicit FakePrimitive(absl::string_view s) : s_(s) {}
   std::string get() { return s_; }
 
  private:
diff --git a/tink/internal/keyset_wrapper_store_test.cc b/tink/internal/keyset_wrapper_store_test.cc
index fc386649a..228e07511 100644
--- a/tink/internal/keyset_wrapper_store_test.cc
+++ b/tink/internal/keyset_wrapper_store_test.cc
@@ -26,6 +26,7 @@
 #include "gtest/gtest.h"
 #include "absl/memory/memory.h"
 #include "absl/status/status.h"
+#include "absl/strings/string_view.h"
 #include "tink/core/key_type_manager.h"
 #include "tink/core/template_util.h"
 #include "tink/input_stream.h"
@@ -61,7 +62,7 @@ using ::testing::Eq;
 
 class FakePrimitive {
  public:
-  explicit FakePrimitive(std::string s) : s_(s) {}
+  explicit FakePrimitive(absl::string_view s) : s_(s) {}
   std::string get() { return s_; }
 
  private:
@@ -148,7 +149,7 @@ std::string AddAesGcmKeyToKeyset(Keyset& keyset, uint32_t key_id,
   key_data.set_type_url("type.googleapis.com/google.crypto.tink.AesGcmKey");
   test::AddKeyData(key_data, key_id, output_prefix_type, key_status_type,
                    &keyset);
-  return key.key_value();
+  return std::string(key.key_value());
 }
 
 // Returns the function that relies on `registry` to transform `key_data` into
diff --git a/tink/internal/registry_impl_test.cc b/tink/internal/registry_impl_test.cc
index c41b631a6..b18ad573b 100644
--- a/tink/internal/registry_impl_test.cc
+++ b/tink/internal/registry_impl_test.cc
@@ -175,7 +175,7 @@ class TestAeadKeyManager : public KeyManager<Aead> {
 // insecure, as it does nothing except provide access to the key.
 class AeadVariant {
  public:
-  explicit AeadVariant(std::string s) : s_(s) {}
+  explicit AeadVariant(absl::string_view s) : s_(s) {}
 
   std::string get() { return s_; }
 
@@ -847,7 +847,7 @@ std::string AddAesGcmKey(uint32_t key_id, OutputPrefixType output_prefix_type,
   key_data.set_type_url("type.googleapis.com/google.crypto.tink.AesGcmKey");
   test::AddKeyData(key_data, key_id, output_prefix_type, key_status_type,
                    &modified_keyset);
-  return key.key_value();
+  return std::string(key.key_value());
 }
 
 // Tests that wrapping of a keyset works in the usual case.
diff --git a/tink/signature/ed25519_sign_key_manager_test.cc b/tink/signature/ed25519_sign_key_manager_test.cc
index 7590ee8f8..87c84c44a 100644
--- a/tink/signature/ed25519_sign_key_manager_test.cc
+++ b/tink/signature/ed25519_sign_key_manager_test.cc
@@ -95,7 +95,7 @@ TEST(Ed25519SignKeyManagerTest, CreateKeyAlwaysNew) {
     StatusOr<Ed25519PrivateKey> key_or =
         Ed25519SignKeyManager().CreateKey(Ed25519KeyFormat());
     ASSERT_THAT(key_or, IsOk());
-    keys.insert(key_or.value().key_value());
+    keys.insert(std::string(key_or.value().key_value()));
   }
   EXPECT_THAT(keys, SizeIs(num_tests));
 }