Patent ID: 7263191

Claim:
A method for encrypting first data such that the participation of t out of n trusted authorities is required to decrypt the encrypted first data, the method comprising executing instructions on a computer apparatus for: dividing the first data into t elements where t>1; setting the value of each coefficient of a polynomial in x of order (t−1) in dependence on a respective one of said elements; deriving n share values by evaluating said polynomial for n different values of x where n≧t; encrypting each share value using as encryption parameters both public data of a respective trust authority and a key string that serves, in relation to that trust authority, as a public key of an intended recipients; providing the encrypted shares, and the values of x used in deriving the shares, to said intended recipient; providing to the intended recipient, from each of t said trust authorities, a private key corresponding to the said public key of the intended recipient in respect of that trust authority; using the private keys to decrypt t encrypted shares; using the decrypted shares to recover the coefficients of said polynomial; and combining the polynomial coefficients to recover the first data.