Method and system for data backup

A backup and restore system comprising:

• a server-side portion that receives backup and restore requests and processes the backup and restore requests by returning encrypted data blocks in response to a restore request, and
• storing encrypted data blocks and file signatures in response to a backup request;
• and
• wherein a file signature includes a header that specifies a file-signature version and an ordered sequence of block descriptors, each block descriptor including a block hash and a block length;
• and
• wherein a file signature is generated from a file by partitioning the file into an ordered sequence of natural blocks;
• and
• coalescing the natural blocks, in order, in a an ordered sequence of approximately fixed-size blocks;
• and
• for each approximately fixed-size block,
• generating a block descriptor that includes an indication of the length of the block and a cryptographic hash of the block;
• and
• appending the header to the generated block descriptors;
• a client-side portion that provides a user-interface that allows files to designated for continuous backup, includes a service process that detects changes to files designated for continuous backup, computes file signatures, computes, by file-signature comparison, blocks needed to be stored for backup and restore operations, and issues requests for backup and restore operations, and
• includes a transport service process for exchanging requests and data with the server-side portion.