Re: Shred mount option for ext4?
On Oct 31, 2006 15:14 -0500, Nikolai Joukov wrote: 1. One of the patches performs N overwrites with configurable patterns (can comply with NIST and NISPOM standards). Because of the transaction compaction we had to separately add overwriting as separate transactions. Fortunately, the whole procedure is still atomic due to the orphan list. The problem that we have right now is per-file syncing of dirty data buffers between overwrites. We sync the whole device at the moment. Did anyone discuss doing this with crypto instead of actually overwriting the whole file? It would be pretty easy to store a per-file crypto key in each inode as an EA, then to delete the file all that would be needed would be to erase the key in a secure matter (which is a great deal easier because inodes don't move around on disk). The drawback is there is a runtime overhead to encrypt/decrypt the file data, but honestly, if people care about secure deletion don't they also care about security of the undeleted data also? By having an (unknown to the user) per-file crypto key then if the file is deleted the user can also plausibly deny the ability to recover the file data even if they are forced to surrender their key. Cheers, Andreas -- Andreas Dilger Principal Software Engineer Cluster File Systems, Inc. - To unsubscribe from this list: send the line unsubscribe linux-ext4 in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Shred mount option for ext4?
Andreas Dilger wrote: On Oct 31, 2006 15:14 -0500, Nikolai Joukov wrote: 1. One of the patches performs N overwrites with configurable patterns (can comply with NIST and NISPOM standards). Because of the transaction compaction we had to separately add overwriting as separate transactions. Fortunately, the whole procedure is still atomic due to the orphan list. The problem that we have right now is per-file syncing of dirty data buffers between overwrites. We sync the whole device at the moment. Did anyone discuss doing this with crypto instead of actually overwriting the whole file? It would be pretty easy to store a per-file crypto key in each inode as an EA, then to delete the file all that would be needed would be to erase the key in a secure matter (which is a great deal easier because inodes don't move around on disk). This is an interesting idea with some annoying implementation details. For example, we would still need to shred that data block used to store the EA in order to prevent key recovery. Also interesting to note that various people are putting encryption into various offload parts which could be useful in this context. The drawback is there is a runtime overhead to encrypt/decrypt the file data, but honestly, if people care about secure deletion don't they also care about security of the undeleted data also? By having an (unknown to the user) per-file crypto key then if the file is deleted the user can also plausibly deny the ability to recover the file data even if they are forced to surrender their key. Cheers, Andreas -- I think that having the data encrypted on disk is a generically useful feature, but in this case it might not count for much since the key is stored right next to the data in that EA... ric - To unsubscribe from this list: send the line unsubscribe linux-ext4 in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: Shred mount option for ext4?
1. One of the patches performs N overwrites with configurable patterns (can comply with NIST and NISPOM standards). Because of the transaction compaction we had to separately add overwriting as separate transactions. Fortunately, the whole procedure is still atomic due to the orphan list. The problem that we have right now is per-file syncing of dirty data buffers between overwrites. We sync the whole device at the moment. Did anyone discuss doing this with crypto instead of actually overwriting the whole file? It would be pretty easy to store a per-file crypto key in each inode as an EA, then to delete the file all that would be needed would be to erase the key in a secure matter (which is a great deal easier because inodes don't move around on disk). Encryption is another possible secure deletion solution. Usually it is used by systems that already encrypt the data anyways. In that case the key management and run-time overhead costs are already paid. The drawback is there is a runtime overhead to encrypt/decrypt the file The difference is that in case of encryption there are overheads for read and write operations whereas in case of overwriting there are overheads only for infrequent unlink/truncate operations. I think that having the data encrypted on disk is a generically useful feature, but in this case it might not count for much since the key is stored right next to the data in that EA... Agreed. Key management is a big issue in any encryption system. In this particular solution the key management is simple but there is also no real protection of the live data. Nikolai. - To unsubscribe from this list: send the line unsubscribe linux-ext4 in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
