Code-based public key encryption (PKE) is a popular choice to achieve post-quantum security, partly due to its capability to achieve fast encryption/decryption. However, code-based PKE has larger ciphertext and public key sizes in comparison to conventional PKE schemes (e.g., those based on RSA). In 2018, Lau and Tan proposed a new rank metric code-based PKE scheme, which has smaller public key and ciphertext sizes compared to other code-based PKE schemes. They also proved that their scheme achieves IND-CPA security, assuming the intractability of the decisional rank syndrome decoding problem. It is known that IND-CCA2 security is the strongest and most popular security assurance for PKE schemes. Therefore, in this paper, we obtain a new code-based PKE scheme from Lau and Tan’s scheme, in order to inherit the underlying small public key and ciphertext sizes. However, our new scheme is shown to achieve IND-CCA2 security, instead of the weaker IND-CPA security. Specifically, the respective public key size and ciphertext size in our new scheme are 15.06 KB and 1.37 KB under 141-bit security level, and 16.76 KB and 1.76 KB under 154-bit security level. We then present a use case for the proposed scheme, that is for secure cloud storage.

中文翻译：

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IND-CCA2安全的量子后加密方案和安全的云存储用例

基于代码的公共密钥加密（PKE）是实现后量子安全性的一种流行选择，部分原因是它具有实现快速加密/解密的能力。但是，与传统的PKE方案（例如，基于RSA的PKE方案）相比，基于代码的PKE具有更大的密文和公钥大小。在2018年，Lau和Tan提出了一种新的基于秩度量代码的PKE方案，与其他基于代码的PKE方案相比，其公钥和密文大小更小。他们还证明了他们的方案达到了IND-CPA的安全性，并假设了决策秩综合症解码问题的顽固性。众所周知，IND-CCA2安全性是PKE方案最强大，最受欢迎的安全性保证。因此，在本文中，我们从Lau和Tan的方案中获得了一种新的基于代码的PKE方案，为了继承底层的小公钥和密文大小。但是，我们的新方案显示出可以实现IND-CCA2安全性，而不是较弱的IND-CPA安全性。具体而言，在新方案中，分别在141位安全级别下的公共密钥大小和密文大小分别为15.06 KB和1.37 KB，在154位安全级别下的公共密钥大小和密文大小分别为16.76 KB和1.76 KB。然后，我们为提出的方案提供一个用例，即用于安全的云存储。