Sets of encryption keys useful by devices for decrypting encrypted content are
defined using an error-correcting code such as a Reed-Solomon code to define vectors
of length "n" over an alphabet of (0, . . . , N-1), wherein "n" is the number of
columns in a key matrix and "N" is the number of rows in the matrix. Each vector
represents a set of keys that can be assigned to a device. With this invention,
overlap between sets of keys can be minimized to minimize the possibility that
the key set of an innocent device might be inadvertently revoked when the key set
of a compromised device is revoked. Also, only the generating matrix of the error-correcting
code and the index of one set of keys need be stored in memory, since all previously
defined key sets can be regenerated if need be from just the generating matrix
and index.
