Necessity and realization of universally verifiable secret sharing

Argues the necessity of universally verifiable secret sharing for secrets as individual users' cryptographic keys, and proposes protocols to realize such secret sharing for two most common public-key cryptosystems: discrete logarithm-based and integer factorization-based. The universal verifiability achieves the sharing of secrets with multiple third parties as shareholders using two-party protocols in which a single verifier, who can be anybody, can verify the correctness of the secret sharing for the (off-line) multiple shareholders. Several advantages result: (i) dropping of the honesty requirement on the verifier and the shareholders, (ii) dropping of the online availability requirement on the multiple shareholders, and (iii) the simplicity of two-party protocols which provide users with the freedom and flexibility to choose multiple shareholders they trust in real time of share distribution. The two-party protocols proposed offer a practical solution for secure data backup and key recovery services.