1. A method for protecting data for N users using N passphrases respectively known to the N users such that N is at least 2, comprising: encrypting data using a master key according to a first symmetric encryption algorithm, to provide encrypted data; deriving a key encryption key for each user from the passphrase known to each user; encrypting the master key using the key encryption key of each user according to a second symmetric encryption algorithm, to provide an encrypted master key for each user; deriving a verification key for each user from the passphrase known to each user, said verification key for each user differing from said key encryption key for each user; and posting the encrypted data along with an ancillary file for access by the user, said ancillary file comprising a user identifier specific to each user, the encrypted master key for each user, and the verification key for each user.
2. The method of claim 1 , wherein the ancillary file comprises N records and three columns, wherein the N records are respectively associated with the N users, and wherein the three columns comprise a column that includes a user identifier of each user, a column that includes the encrypted master key for each user, and a column that includes the verification key for each user.