Secret Key Extraction Over Unauthenticated Public Channels

Sandro Coretti, Ueli M. Maurer, Björn Tackmann

Wenwen Tu, Lifeng Lai

In this paper, the problem of key generation over an unauthenticated public channel in a network setup is considered. The considered model consists of four terminals: two legitimate terminals who need to share a key, a helper and an active adversary. The legitimate terminals and the helper are allowed to exchange messages over a public noiseless channel, to which the adversary has full access and may modify messages exchanged through this public channel. We investigate two types of keys: secret key (secure from the adversary only) and private key (secure from both the helper and the adversary). We characterize the relationship between the key rates in our model and the existing models with a passive adversary. We characterize conditions under which the generated key rates in this model are non-zero, and further provide an authentication scheme to show that key capacities, if are non-zero, are the same as those for the scenario with a passive adversary.

Stephan Ludwig, R. Guillaume, A. Müller +1 more

Ueli M. Maurer, Stefan Wolf

For pt.I see ibid., vol.49, no.4, p.822-31(2003). In the first part, we showed that when two parties, willing to generate a secret key, but connected only by a completely insecure communication channel, have access to independent repetitions of some random experiment, then the possibility of secret-key agreement depends on a certain property, called simulatability, of the probability distribution modeling the parties' initial knowledge. More generally, the simulatability condition is important in the context of identification and authentication among parties sharing some correlated but not necessarily identical partially secret keys. Unfortunately, this condition is a priori not very useful since it is not clear how to decide efficiently whether it is satisfied or not for a given distribution P/sub XYZ/. We introduce a new formalism, based on a mechanical model for representing the involved quantities, that allows for dealing with discrete joint distributions of random variables and their manipulations by noisy channels. We show that this representation leads to a simple and efficient characterization of the possibility of secret-key agreement secure against active adversaries.

Xiaojun Sun, Wei Xu, Ming Jiang +1 more

Physical layer secret key can be extracted from wireless fading channels based on channel quantization with guardband (CQG). In this paper, we analyze the key generation efficiency of the CQG protocol. Analytical closed-form expressions of bit error rate (BER) and key generation efficiency are derived for the CQG protocol. In order to further improve the key generation efficiency, we concatenate the CQG protocol with reconciliation. And then, we present a upper bound of key generation efficiency, which can be maximized by careful selecting the guardband region and LDPC codes. The key generation efficiency is also analyzed by considering the attacks in the case of an unauthenticated wireless channel.

Hoon Wei Lim