An encryption apparatus and method for providing an encrypted file system
are provided. The encryption apparatus and method of the illustrative
embodiments uses a combination of encryption methodologies so as to
reduce the amount of decryption and re-encryption that is necessary to a
file in the Encrypted File System in the event that the file needs to be
modified. The encryption methodologies are interleaved, or alternated,
with regard to each block of plaintext. In one illustrative embodiment,
Plaintext Block Chaining (PBC) and Cipher Block Chaining (CBC) encryption
methodologies are alternated for encrypting a sequence of blocks of data.
The encryption of a block of plaintext is dependent upon the plaintext or
a cipher generated for the plaintext of a previous block of data in the
sequence of blocks of data so that the encryption is more secure than
known Electronic Code Book encryption methodologies.