In this work, we present the first secure stegosystem in the common computational model which, for any communication channel, is provably secure, reliable, and has nearly optimal bandwidth, but needs super-polynomial time. This solves several open problems about secret-key steganography in the computational model. In particular, our result answers affirmatively the question whether there exists a secure and reliable universal system of rate asymptotically larger than $\log \kappa$, where κ is the security parameter. Next, we prove a lower bound on the query complexity of stegosystems showing that our construction is optimal. This lower bound extends the results by Hopper et al. (2009) [19] and by Dedić et al. (2009) [22]. We also discuss universal steganography of optimal rate in the information-theoretic setting. We prove that an exponential number of samples is needed to embed messages in documents of high min-entropy. Our results, together with the result by Cachin (2004) [16], show that the situation of universal steganography in the computational and in the information-theoretic model is analogous: optimal universal steganography exists, but the protocols need super-polynomial time.

在这项工作中，我们提出了通用计算模型中的第一个安全隐身系统，对于任何通信通道，该系统都可证明是安全，可靠的，并且具有近乎最佳的带宽，但是需要超多项式时间。这解决了计算模型中有关秘密密码术的几个开放问题。特别是，我们的结果肯定地回答了以下问题：是否存在一个渐近大于$\mathrm{日志}\kappa$，其中κ是安全性参数。接下来，我们证明了隐身系统查询复杂度的下限，表明我们的构造是最优的。这个下限扩展了Hopper等人的结果。（2009）[19]和Dedić等人。（2009）[22]。我们还将讨论信息理论环境中最佳速率的通用隐写术。我们证明将消息嵌入高最小熵的文档中需要成倍数量的样本。我们的结果以及Cachin（2004）[16]的结果表明，在计算模型和信息理论模型中通用隐写术的情况类似：存在最佳通用隐写术，但是协议需要超多项式时间。