The Design of the {OpenBSD} Cryptographic Framework

Cryptographic transformations are a fundamental building block in many security applications and protocols. To improve performance, several vendors market hardware accelerator cards. However, until now no operating system provided a mechanism that allowed both uniform and efficient use of this new type of resource. We present the OpenBSD Cryptographic Framework (OCF), a service virtualization layer implemented inside the kernel, that provides uniform access to accelerator functionality by hiding card-specific details behind a carefully-designed API. We evaluate the impact of the OCF in a variety of benchmarks, measuring overall system performance, application throughput and latency, and aggregate throughput when multiple applications make use of it. We conclude that the OCF is extremely efficient in utilizing cryptographic accelerator functionality, attaining 95% of the theoretical peak device performance, and over 800 Mbit/sec aggregate throughput using 3DES. We believe that this validates our decision to opt for ease of use by applications and kernel components through a uniform API, and for seamless support for new accelerators. Furthermore, our evaluation points to several bottlenecks in system and operating system design: data copying between user and kernel modes, PCI bus signaling inefficiency, protocols that use small data units, and single-threaded applications. We offer several suggestions for improvements and directions for future work.

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