Strong secrecy for erasure wiretap channels

We show that duals of certain low-density parity-check (LDPC) codes, when used in a standard coset coding scheme, provide strong secrecy over the binary erasure wiretap channel (BEWC). This result hinges on a stopping set analysis of ensembles of LDPC codes with block length n and girth ⋛ for some ⋛. We show that if the minimum left degree of the ensemble is lmin, the expected probability of block error is O(1/n⌈^l min^k/2⌉ −k) when the erasure probability ∊ < ∊ef, where ∊ef depends on the degree distribution of the ensemble. As long as lmin and k > 2, the dual of this LDPC code provides strong secrecy over a BEWC of erasure probability greater than 1–∊ef.