TWC: Small: Theory and Practice of Tweakable-Blockcipher-Based Cryptography

块密码是共享密钥密码术的基本构建块。然而，对于某些重要的加密目标，如构建加密方案，分组密码提供的接口是有限的。一种更现代的原始密码，可调整分组密码(TBC)，通常是更合适的。像块密码一样，TBC接受密钥、数据块和TWEY作为输入，TWEY是额外的输入，它为TBC的输入输出行为提供可变性，而不必更改密钥。基于TBC的密码学具有比类似的基于分组密码的设计具有更好的安全性和高效构造的潜力，以及对相关数据输入、密钥重用和其他实用考虑的自然支持。尽管基于TBC的密码学有着明确的前景，但基于TBC的密码学尚未得到持续和一致的检验。该项目提供了这样的检查，以努力更好地了解TBC对未来加密实践的影响的潜力。它探索了TBC的构建，包括从头开始和利用现成的原语。它重新考虑了现有的基于分组密码的构造，从“如果我们用TBC替换分组密码会发生什么？”的问题开始，并导致了具有更高安全性的新设计，以及对某些实现和使用错误的更大弹性。它还考虑了与TBC安全定义有关的基本问题，以及与理想化密码模型的联系。

Blockciphers are the basic building block of shared-key cryptography. However, for certain important cryptographic goals, like building encryption schemes, the interface presented by blockciphers is limiting. A more modern primitive, the tweakable blockcipher (TBC), is often a better fit. Like a blockcipher, a TBC takes as input a secret key, a block of data and the tweak which is an additional input which provides variability to the TBC's input-output behavior without having to change the secret key. TBC-based cryptography has the potential to deliver efficient constructions with better security than analogous blockcipher-based designs, as well natural support for associated data inputs, key reuse, and other practical considerations.Despite its clear promise, TBC-based cryptography has not received a sustained and coherent examination. This project provides such an examination, in an effort to better understand the potential of TBCs to impact future cryptographic practice. It explores the construction of TBCs, both from scratch and leveraging off-the-shelf primitives. It reconsiders existing blockcipher-based constructions starting from the question, "what happens if we replace the blockcipher with a TBC?", and leading to new designs with increased security, and greater resilience to certain implementation and usage mistakes. It also considers foundational matters concerning definitions of security for TBCs, and connections to idealized models of ciphers.