A
(r,n)-threshold secret-sharing scheme is a fundamental
cryptographic structure, allowing a dealer to divide a
secret into n shares, distribute them among a group of
n shareholders in such a way that the secret is reconstructible
from any r shareholders, but even complete knowledge of
r-1 pieces can not uniquely determine the secret. A common
application for threshold secret-sharing schemes is to
achieve robustness of distributed security systems. In
many settings, the system value and attacker capabilities
are likely to change over time, thus requiring the security
policy and hence threshold parameter r to vary over time.
As a consequence, we may need to modified threshold parameter
after the setup of a secret sharing scheme. The talk will
give a upper bound of the compromise of security and share
size for threshold-changeable secret sharing scheme, and
propose a new Chinese remainder theorem(CRT) based construction,
which meets the bound and have some improvements.