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

components/os_crypt/key_storage_linux.h

Index: components/os_crypt/key_storage_linux.h
diff --git a/components/os_crypt/key_storage_linux.h b/components/os_crypt/key_storage_linux.h
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+++ b/components/os_crypt/key_storage_linux.h
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+// Copyright 2016 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.
+
+#ifndef COMPONENTS_OS_CRYPT_KEY_STORAGE_LINUX_H_
+#define COMPONENTS_OS_CRYPT_KEY_STORAGE_LINUX_H_
+
+#include <memory>
+#include <string>
+
+#include "base/macros.h"
+
+// An API for retrieving OSCrypt's password from the system's password storage
+// service.
+class KeyStorageLinux {
+ public:
+  KeyStorageLinux() = default;
+  virtual ~KeyStorageLinux() = default;
+
+  // Tries to load all known key storages. Returns the first that succeeds or
+  // null if none succeed.
+  static std::unique_ptr<KeyStorageLinux> CreateService();
+
+  // Gets the encryption key from the OS password-managing library. If a key is
+  // not found, a new key will be generated, stored and returned.
+  virtual std::string GetKey() = 0;
+
+ protected:
+  // Loads the key storage. Returns false if the service is not available.
+  virtual bool Init() = 0;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(KeyStorageLinux);
+};
+
+#endif  // COMPONENTS_OS_CRYPT_KEY_STORAGE_LINUX_H_