KPaM: A Key Protection Framework for Mobile Devices Based on Twoparty Computation Key protection on mobile devices is attracting more attention with the rapid growth of mobile payment. There are many key protection methods proposed in academia from the following three aspects. The first is from algorithmic perspective, such as whitebox cryptography. The second is from physical protection perspective, such as secure element (SE). The last is from key escrow perspective, such as cloud secure element (Cloud SE). The security of the white box cryptography has not yet reached an agreement in academia, and SE cannot defend against unknown side channel attacks in the future since it can hardly be updated. With regard to Cloud SE, the user has to totally trust the cloud, including the cloud provider, the cloud environment, etc. However, with the development of attack methods, the complete credibility of the cloud has gradually become an excessive requirement.In this paper, we propose KPaM, a lowcost and flexible key protection framework for mobile devices, which can mitigate the issues described above. The main idea of KPaM is inspired by emerging twoparty computation algorithm. The private key is split into two parts, stored and used in the mobile device and the cloud respectively. The cloud does not store the complete key, so there is no need to worry about the abuse of the userxe2x80x99s private key. On the mobile side, we get rid of SE and use TEE (trusted execution environment) to perform cryptographic operations and access control mechanism, which realizes the functions of secure storage and trust path. At last, we take SM2 algorithm as an example to validate KPaM and evaluate its security and efficiency.

Extending NCP for protocols using public keys One of the greatest obstacles to widespread deployment of wireless mobile systems is security. Cryptographically strong protocols and algorithms are required to enable secure communication over links that are easy to monitor and control by an attacker. While good cryptographic algorithms exist, it is difficult to design protocols that are immune to malicious attack. Good analysis techniques are lacking. This paper presents extensions to a technique for specifying and analyzing nonmonotonic cryptographic protocols that use asymmetric keys. We introduce new actions and inference rules, as well as slight modifications to the Update function. An important observation is that reasoning about the origin of messages is quite different when dealing with asymmetric key protocols. We also introduce the notion that keys in certificates should be bound to the principals receiving them. We extend the technique to meet the binding requirements and show how the flaw in the Denning and Sacco public key protocol, which was discovered by Abadi and Needham, is revealed. We demonstrate the extended technique using one protocol of our own and the Needham and Schroeder public key protocol. We also introduce and analyze a fix to a known weakness in Needham and Schroederu0027s protocol using our extended technique. Finally, we present several applications of these techniques to protocols for mobile computing over wireless networks.