Traditionally, cryptographic protocols rely on mathematical assumptions and results to establish security guarantees. Quantum cryptography has demonstrated how physical properties of a communication channel can be leveraged in the design of cryptographic protocols, too. Our starting point is the AlphaEta protocol, which was designed to exploit properties of coherent states of light to transmit data securely over an optical channel. AlphaEta aims to draw security from the uncertainty of any measurement of the transmitted coherent states due to intrinsic quantum noise. We present a technique to combine AlphaEta with classical preprocessing, taking into account error-correction for the optical channel. This enables us to establish strong provable security guarantees. In addition, the type of hybrid encryption we suggest, enables trade-offs between invoking a(n inexpensive) classical communication channel and a (more complex to implement) optical channel, without jeopardizing security. Our design can easily incorporate fast state-of-the-art authenticated encryption, but in this case the security analysis requires heuristic reasoning.

Assuming the availability of an existentially unforgeable signature scheme and an (IND- CCA secure) key encapsulation mechanism, we present a generic construction for group key establishment. The construction is designed with existing proposals for post-quantum cryptography in mind. Applied with such existing proposals and assuming their security, we obtain a quantum-safe three-round protocol for authenticated group key establishment that requires only one signature per protocol participant.

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Motivated by the problem of establishing a session key among parties based on the possession of certain credentials only, we discuss a notion of attribute-based key establishment. A number of new issues arise in this setting that are not present in the usual settings of group key establishment where unique user identities are assumed to be publicly available.After detailing the security model, we give a two-round solution in the random oracle model. As main technical tool we introduce a notion of attribute-based signcryption, which may be of independent interest. We show that the type of signcryption needed can be realized through the encrypt-then-sign paradigm. Further, we discuss additional guarantees of the proposed protocol, that can be interpreted in terms of deniability and privacy.

Identity-based non-interactive key distribution (ID-NIKD) is a cryptographic primitive that enables two users to establish a common secret key without exchanging messages. All users of the system have access to public system parameters and a private key, obtained through the help of a trusted key generation center. In this contribution, we discuss how to capture an intuitive form of forward security for ID-NIKD schemes in a security model. Building on results of Sakai et al. as well as of Paterson and Srinivasan, we discuss how the proposed notion of forward security can be achieved in the random oracle model, using a Bilinear Diffie-Hellman assumption in combination with a forward-secure pseudorandom bit generator. We also show how a forward-secure ID-NIKD scheme can be used to realize forward-secure identity-based encryption.