We describe a public-key cryptosystem with worst-case/average case
equivalence. The cryptosystem has an amortized plaintext to
ciphertext expansion of O(n), relies on the hardness of the
\tilde O(n^2)-unique shortest vector problem for lattices, and
requires a public key of size at most O(n^4) bits. The new
cryptosystem generalizes a conceptually simple modification of the
``Ajtai-Dwork'' cryptosystem. We provide a unified treatment of the
two cryptosystems.