Martin Hostettler 620f505a14 Reserve nonce space for AES-CTR before using it. ... Reusing the nonce totally breaks AES-CTR confidentiality. This code uses a reservation of nonce space and stores the next nonce available for a future reservation on the client and in the repository. Local storage is needed to protect against evil repositories that try to gain access to encrypted data by not saving nonce reservations and aborting the connection or otherwise forcing a rollback. Storage in the repository is needed to protect against another client writing to the repository after a transaction was aborted and thus not seeing the last used nonce from the manifest. With a real counter mode cipher protection for the multiple client case with an actively evil repository is not possible. But this still protects against cases where the attacker can not arbitrarily change the repository but can read everything stored and abort connections or crash the server. Fixes #22		2016-08-27 15:31:50 +02:00
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borg	Reserve nonce space for AES-CTR before using it.	2016-08-27 15:31:50 +02:00