Traditional X.509 public key infrastructures (PKIs) depend on trusted certification authorities (CAs) to sign certificates, used in SSL/TLS to authenticate web servers and establish secure channels. However, recent security incidents indicate that CAs may (be compromised to) sign fraudulent certificates. In this article, we propose blockchain-based certificate transparency (CT) and revocation transparency (RT) to balance the absolute authority of CAs. Our scheme is compatible with X.509 PKIs but significantly reinforces the security guarantees of a certificate. The CA-signed certificates and their revocation status information of an SSL/TLS web server are published by the subject (i.e., the web server) as a transaction in the global certificate blockchain. The certificate blockchain acts as append-only public logs to monitor CAs’ certificate signing and revocation operations, and an SSL/TLS web server is granted with the cooperative control on its certificates. A browser compares the certificate received in SSL/TLS negotiations with the ones in the public certificate blockchain, and accepts it only if it is published and not revoked. We implement the prototype system with Firefox and Nginx, and the experimental results show that it introduces reasonable overheads.

The video conference has been widely adopted for telecommuting due to the convenience, and various schemes are proposed to provide the confidentiality and integrity of the stream data. However, due to the limitation of the video terminals, the adversary can still obtain the cryptographic key by exploiting the vulnerabilities of OS or other binaries in the video terminals, or launching various attacks such as cold-boot attacks, DMA attacks and side channel attacks. Once the cryptographic key is leaked, the confidentiality and integrity of the stream data will be broken. In this paper, we propose a secure video conference system by customizing the cryptographic USB key (called CCUK) for efficient cryptographic computation and secure key storage. In our scheme, the cryptographic key is stored and used (i.e., key agreement and data encryption/decryption) in CCUK, a dedicated hardware security module (HSM), which avoids the leakage of cryptographic key even when the video terminal is compromised. Moreover, CCUK only has one requirement on the video terminal, i.e., having the USB interface, and therefore can be deployed in almost all types of video terminals. CCUK is cost-effective compared to other types of HSMs, and its efficiency avoids the stream data encryption/decryption to be the performance bottleneck. We have implemented the proposed scheme, and deployed it to provide the confidentiality and integrity for a practical video conference system. The evaluation demonstrates that CCUK can support 1080P HD video conference.

Cryptography is essential for computer and network security. When cryptosystems are deployed in computing or communication systems, it is extremely critical to protect the cryptographic keys. In practice, keys are loaded into the memory as plaintext during cryptographic computations. Therefore, the keys are subject to memory disclosure attacks that read unauthorized data from RAM. Such attacks could be performed through software exploitations, such as OpenSSL Heartbleed, even when the integrity of the victim system's binaries is maintained. They could also be done through physical methods, such as cold-boot attacks, even if the system is free of software vulnerabilities. This paper presents Mimosa, to protect RSA private keys against both software-based and physical memory disclosure attacks. Mimosa uses hardware transactional memory (HTM) to ensure that (a) whenever a malicious thread other than Mimosa attempts to read the plaintext private key, the transaction aborts and all sensitive data are automatically cleared with hardware, due to the strong atomicity guarantee of HTM; and (b) all sensitive data, including private keys and intermediate states, appear as plaintext only within CPU-bound caches, and are never loaded to RAM chips. To the best of our knowledge, Mimosa is the first solution to use transactional memory to protect sensitive data against memory attacks. However, the fragility of TSX transactions introduces extra cache-clogging denial-of-service (DoS) threats, and attackers could sharply degrade the performance by concurrent memory-intensive tasks. To mitigate the DoS threats, we further partition an RSA private-key computation into multiple transactional parts by analyzing the distribution of aborts, while (sensitive) intermediate results are still protected across transactional parts. Through extensive experiments, we show that Mimosa effectively protects cryptographic keys against attacks that attempt to read sensitive data in memory, and introduces only a small performance overhead, even with concurrent cache-clogging workloads.

User registration is the beginning of the life cycle of an account for most information systems. Some registration servers have special requirements for the validity of the registrant's identity and attributes, and thus demand his real-life identity and raw attributes for verification, which poses a great threat to privacy. However, the exposure of the registrant's real-life identity and raw attributes is not necessary, as long as he can prove to the server that he is associated with a real-life identity (RId) that fulfills the requirements. In this paper, we propose the concept of anonymous registration, with which a user can register an anonymous identity (AId) without privacy leakage. Anonymous registration has two basic features, i.e. privacy and verifiability, and two extended features, i.e. traceability and revocability. We design and implement an anonymous registration scheme with the above features, named Traceable Revocable Anonymous Registration Scheme (TRARS) based on Blockchain. In the proposed registration process, the user can calculate a zero-knowledge proof for a self-generated AId, which can prove to the registration server that the AId is associated with a valid RId and the RId's attributes meet the server's requirements, without leaking any privacy. We also introduce an identity revocation coordinator, with which evil identities can be tracked and outdated AIds can be revoked timely.

FIDO2, the newest set of FIDO specifications, enables the user to leverage an external authenticator for the authentication in both mobile and desktop environments (referred to as user agent). For the secure registration and authentication, FIDO2 requires the external authenticator and user agent to establish a confidential and mutually authenticated data transport channel through either USB interfaces, Near Field Communication (NFC) or Bluetooth. However, the external authenticator and host may not be equipped with one of the above physical media simultaneously, for example, a desktop may only have USB interfaces while an external authenticator (e.g., a smartphone) may have no USB inferfaces. This affects the wide adoption of FIDO2. In this paper, we extend the registration and authentication processes of FIDO2 external authenticator with QR code, which enables the external authenticator being equipped with a camera to be used for the authentication at any user agent. During the registration process, our scheme requires the user to provide the original credential and a one-time password displayed on the authenticator, and therefore ensures the correct user will only be bound with the expected authenticator. The security of our scheme has been formally analyzed based on the Dolev-Yao style model, a widely adopted model for the analysis of web systems. We have implemented the prototype, and the performance evaluation demonstrated the efficiency of our scheme, which needs 373 ms for registration and 141 ms for authentication in our environment.

With the emergence of virtualization technologies, various services have been migrated to the cloud. Beyond the tenants' own security controls implemented in the virtual machine (VM), the binary integrity verification mechanism in the virtual machine manager (VMM) provides stronger protections against malware. Unfortunately, none of existing integrity verification mechanisms in the cloud provides complete transparency and fine-grained efficiency. Some schemes selectively check the integrity of sensitive binaries, but they require modifications to the VMs (e.g., integrating monitoring libraries) to trigger verification. Others, although need no modification to the VMs, have to enforce checking on all the binaries, because they cannot distinguish binary images for the sensitive processes from the binaries for insensitive ones, leading to significant performance overheads. In this paper, we present TF-BIV, a transparent and fine-grained binary integrity verification scheme, which does not require any modification or software/driver installation in the VM. TF-BIV identifies the sensitive processes at the creation, and checks the integrity of the binaries (including the guest OS kernel and the dependant binaries) related to these processes. The provided transparency and efficiency are achieved by leveraging existing hardware virtualization supports (i.e., Intel extended page table) and debugging features (i.e., monitor trap flag). We have implemented the TF-BIV prototype based on QEMU-KVM. To demonstrate the usability of TF-BIV, we adopted it for cloud-based cryptographic services, to achieve the strict invoking controls. In addition to the password-based authentication, TF-BIV further achieves process-level authorization to the invokers. Intensive evaluation shows that TF-BIV implements the designed binary integrity verification with only about 3.6% performance overhead.

Information systems are deployed in clouds as virtual machines (VMs) for better agility, elasticity and reliability. It is necessary to safekeep their cryptographic keys, e.g., the private keys used in TLS and SSH, against various attacks. However, existing virtualization solutions do not improve the cryptography facilities of in-cloud systems. This paper presents SECRIN, a secure cryptography infrastructure for VMs in the cloud. SECRIN is composed of a) virtual cryptographic devices implemented in VM monitors (VMMs), and b) a device management tool integrated in the virtualization management system. A virtual device receives requests from VMs, computes with cryptographic keys within the VMM and returns results. The keys appear only in the VMM's memory space, so that they are kept secret even if the VMs were compromised. With the management tool, the operator of virtualization management systems assigns virtual cryptographic devices to a VM as well as other resources, while the tenant (or owner) of a VM still holds proper controls on the keys. The virtual devices work compatibly with live migration, and the cryptographic computations are not interrupted when the VMs are moving from a host to another. We develop the SECRIN prototype with KVM-QEMU and oVirt. Experimental results show that, it works compatibly with existing virtualization solutions, provides reliable cryptographic computing services for applications, and is secure against attacks happening in VMs.

Version control systems (VCS), including central VCS (CVCS) and distributed VCS (DVCS), are widely adopted to manage the changes to various types of data. Unlike the CVCS where all the entities obtain the data from the server and the access control is enforced with the cooperation of the server, each entity in the DVCS stores the entire repository, obtains the repository shared by any entity and is free to share its own repository. Therefore, existing access control schemes for CVCS are not suitable for DVCS. In this paper, we present a distributed access control scheme (Disac) for DVCS. Disac makes each entity have the whole control on its data, while the access control is enforced at each entity independently. We adopt Attribute-based Encryption (ABE) and Attribute-based Signature (ABS) to achieve the read and write permission control. The analysis of the Git client demonstrates that Disac is easy to be integrated.

Cache timing side channels allow a remote attacker to disclose the cryptographic keys, by repeatedly invoking the encryption/decryption functions and measuring the execution time. Warm and Delay are two algorithm-independent and implementation-transparent countermeasures against remote cache-based timing side channels for block ciphers. They destroy the relationship between the execution time and the cache misses/hits which are determined by the secret key, but bring remarkable performance overhead. In this paper, we investigate the performance of cryptographic functions protected by Warm and Delay, and attempt to find the best strategy to integrate these two countermeasures with the optimal performance while effectively eliminate remote cache timing side channels for block ciphers implementations with lookup tables. To the best of our knowledge, this work is the first to systematically analyze the performance of integrating Warm and Delay against cache side channels.We derive the optimal scheme to integrate Warm and Delay, and apply it to AES. It is proven that the integration scheme achieves the optimal performance with the least extra operations on commodity systems. Finally, we implement it on Linux with Intel CPUs. Experimental results confirm that, ( a) the execution time does not leak information on cache access, ( b) the scheme outperforms other integration strategies of Warm and Delay, and ( c) the implementation works without any privileged operations on the computer.