A content delivery network and method employing a Downloadable Conditional Access System (“DCAS”) includes first and second personalization servers. A unit key list having unique keys is segmented into different blocks. Each block is encrypted with a separate transmission key corresponding to that block such that first and second blocks are respectively encrypted with first and second transmission keys. The encrypted blocks are communicated to the personalization servers. The first transmission key is communicated to the first personalization server without being communicated to another personalization server such that the first server can decrypt the first block using the first transmission key to access the keys of the first block. The second transmission key is communicated to the second personalization server without being communicated to another personalization server such that the second server can decrypt the second block using the second transmission key to access the keys of the second block.