Patent ID: 7095858

Claim:
A method for constructing an encrypted file comprising the steps of: obtaining a first key and a second key having a same size; obtaining a third key that is constructed by rearranging and combining the first and second keys, wherein the third key is larger in size than the first and second keys; obtaining a fourth key that is constructed by selecting a subset of the third key, wherein the fourth key is smaller in size than the first, second and third keys; encrypting ( 210 ) a source file ( 256 ) by encrypting a plurality of segments of the source file ( 256 ) using the fourth key to generate a first encrypted file ( 260 ), the size of each segment being equal in size to the fourth key; and encrypting ( 216 ) the first encrypted file ( 260 ) by encrypting a plurality of blocks of the first encrypted file ( 260 ) using the third key to generate a second encrypted file ( 268 ), the size of each block being equal in size to the third key.