Distributed Online Social Networks (DOSNs) have been proposed to shift the control over user data from a unique entity, the online social network provider, to the users of the DOSN themselves. In this paper we focus on the problem of preserving the privacy of the contents shared to large groups of users. In general, content privacy is enforced by encrypting the content, having only authorized parties being able to decrypt it. When efficiency has to be taken into account, new solutions have to be devised that: i) minimize the re-encryption of the contents published in a group when the composition of the group changes; and, ii) enable a fast distribution of the cryptographic keys to all the members ($n$n) of a group, each time a set of users is removed from or added to the group by the group owner. Current solutions fall short in meeting the above criteria, while our approach requires only $O(d\cdot log_d (n))$O(d·logd(n)) encryption operations when a user is removed from a group (where $d$d is an input parameter of the system), and $O(2\cdot log_d (n))$O(2·logd(n)) when a user joins the group. The effectiveness of our approach is evaluated through simulations based on a real online social network.

中文翻译：

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在去中心化在线社交网络中保护内容隐私的基于逻辑密钥层次结构的方法

分布式在线社交网络 (DOSN) 已被提议用于将用户数据的控制权从唯一实体（在线社交网络提供商）转移到 DOSN 的用户本身。在本文中，我们关注保护共享给大量用户的内容的隐私的问题。通常，内容隐私是通过加密内容来强制执行的，只有授权方才能对其进行解密。当必须考虑效率时，必须设计新的解决方案： i) 当组的组成发生变化时，尽量减少对组中发布的内容的重新加密；并且，ii) 能够将加密密钥快速分发给所有成员（$n$n)，每次由组所有者从组中删除或添加一组用户时。当前的解决方案不能满足上述标准，而我们的方法只需要$O(d\cdot log_d (n))$哦(d·升○Gd(n)) 从组中删除用户时的加密操作（其中 $d$d 是系统的输入参数），和 $O(2\cdot log_d (n))$哦(2·升○Gd(n))当用户加入群组时。我们的方法的有效性是通过基于真实在线社交网络的模拟来评估的。