John wrote: > The most obvious methods I can think of create explosive data growth > as M and N increase. The amount of data needed in any way I can think > of grows linearly with M and exponentially with N. The data remains encrypted, until the key is known. So only the key needs to be distributed. Keywords: Reed-Solomon, FEC, Vandermonde matrices, PAR2. Extra requirement is, that you don't want 90% of the key known when M=10 and 9 key-secrets are collected, so you need an extra 'layer'. A change of 1 bit in one 'layer' should change in average 50% of the bits in the next 'layer', because basically you want each key-bit to remain unknown (and unguessable) until (at least) M secrets are known. -- Grtz, Ruud