Abstract: A method for allowing an operating system (OS), to access an encrypted data storage system of a computer, wherein: the data storage system comprises: a partition; and first encrypted data units that comprise partition table data of said data storage system; and said computer is connectable to an external device comprising: a boot loader for an external OS that is not installed on the computer; and partitioning information capturing an expected location of said partition in the data storage system; and wherein second encrypted data units that comprise reference partition table data for said data storage system are available from said computer or said external device, the method comprising: upon connection of said external device to the computer, instructing to boot the computer from said boot loader; and during or after booting of the computer: comparing the first and second encrypted data units; and if the first and second encrypted data units match, allow the external OS to access, based on the partitioning