Distributions Attaining Secret Key at a Rate of the Conditional Mutual Information

Abstract

In this paper we consider the problem of extracting secret key from an eavesdropped source $p_{XYZ}$ at a rate given by the conditional mutual information. We investigate this question under three different scenarios: (i) Alice ($X$) and Bob ($Y$) are unable to communicate but share common randomness with the eavesdropper Eve ($Z$), (ii) Alice and Bob are allowed one-way public communication, and (iii) Alice and Bob are allowed two-way public communication. Distributions having a key rate of the conditional mutual information are precisely those in which a "helping" Eve offers Alice and Bob no greater advantage for obtaining secret key than a fully adversarial one. For each of the above scenarios, strong necessary conditions are derived on the structure of distributions attaining a secret key rate of $I(X:Y|Z)$. In obtaining our results, we completely solve the problem of secret key distillation under scenario (i) and identify $H(S|Z)$ to be the optimal key rate using shared randomness, where $S$ is the Gács-Körner Common Information. We thus provide an operational interpretation of the conditional Gács-Körner Common Information. Additionally, we introduce simple example distributions in which the rate $I(X:Y|Z)$ is achievable if and only if two-way communication is allowed.

References in corpus (2)

• Bound entangled states with a private key and their classical counterpart
• A Classical Analog to Entanglement Reversibility

Cited by in corpus (5)

• Round Complexity in the Local Transformations of Quantum and Classical States
• Communication Cost for Non-Markovianity of Tripartite Quantum States: A Resource Theoretic Approach
• A Classical Analog to Entanglement Reversibility
• Unique Information and Secret Key Decompositions
• Information-theoretically Secure Key Agreement over Partially Corrupted Channels