OSCrypt for POSIX uses libsecret to store a randomised encryption key.

components/os_crypt/os_crypt_unittest.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/os_crypt/os_crypt.h"
 
 #include <string>
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "build/build_config.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace {
 
 class OSCryptTest : public testing::Test {
  public:
   OSCryptTest() {}
 
   void SetUp() override {
 #if defined(OS_MACOSX)
     OSCrypt::UseMockKeychain(true);
 #endif
+#if defined(USE_LIBSECRET)
+    OSCrypt::UseMockKeyStorage(true);
+#endif
   }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(OSCryptTest);
 };
 
 TEST_F(OSCryptTest, String16EncryptionDecryption) {
   base::string16 plaintext;
   base::string16 result;
   std::string utf8_plaintext;
@@ skipping 101 matching lines @@
   ASSERT_TRUE(OSCrypt::EncryptString(plaintext, &ciphertext));
   EXPECT_NE(plaintext, ciphertext);
   ASSERT_LT(4UL, ciphertext.size());
   ciphertext[3] = ciphertext[3] + 1;
   EXPECT_FALSE(OSCrypt::DecryptString(ciphertext, &result));
   EXPECT_NE(plaintext, result);
   EXPECT_TRUE(result.empty());
 }
 
 }  // namespace