Type-Based Analysis of PKCS#11 Key Management

Abstract

Abstract. PKCS#11, is a security API for cryptographic tokens. It is known to be vulnerable to attacks which can directly extract, as cleartext, the value of sensitive keys. In particular, the API does not impose any limitation on the different roles a key can assume, and it permits to perform conflicting operations such as asking the token to wrap a key with another one and then to decrypt it. Fixes proposed in the literature, or implemented in real devices, impose policies restricting key roles and token functionalities. In this paper we define a simple imperative programming language, suitable to code PKCS#11 symmetric key management, and we develop a type-based analysis to prove that the secrecy of sensitive keys is preserved under a certain policy. We formally analyse existing fixes for PKCS#11 and we propose a new one, which is type-checkable and prevents conflicting roles by deriving different keys for different roles.

Type-Based Analysis of Generic Key Management APIs

“…In [6] the authors propose a simple language, for the coding of PKCS#11 APIs, and they develop a type-based analysis to prove that the secrecy of sensitive keys is preserved under a certain policy. This solution, is however limited to PKCS#11 cryptographic APIs and to symmetric keys, whereas in this paper we propose a new language that is applicable to general cryptographic APIs, that is, any key storage that is managed through handles, and that manages also asymmetric and signing keys, in the style of [16].…”

“…We then formalize the attacker model and define API security. The API language is inspired in [6] but here we allow more expressive types that dictate how keys should be used and what is their security level. Moreover we consider asymmetric encryption and digital signatures that are not accounted for in [6].…”