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