From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mailgw-01.dd24.net ([193.46.215.41]:46782 "EHLO mailgw01.dd24.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751833AbbCLDmL (ORCPT ); Wed, 11 Mar 2015 23:42:11 -0400 Received: from mailpolicy-01.live.igb.homer.key-systems.net (mailpolicy-02.live.igb.homer.key-systems.net [192.168.1.27]) by mailgw01.dd24.net (Postfix) with ESMTP id 706745FB30 for ; Thu, 12 Mar 2015 03:35:22 +0000 (UTC) Received: from mailgw01.dd24.net ([192.168.1.35]) by mailpolicy-01.live.igb.homer.key-systems.net (mailpolicy-02.live.igb.homer.key-systems.net [192.168.1.25]) (amavisd-new, port 10235) with ESMTP id aMM4v29MFi-Q for ; Thu, 12 Mar 2015 03:35:20 +0000 (UTC) Received: from heisenberg.fritz.box (ppp-93-104-121-105.dynamic.mnet-online.de [93.104.121.105]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mailgw01.dd24.net (Postfix) with ESMTPSA for ; Thu, 12 Mar 2015 03:35:20 +0000 (UTC) Message-ID: <1426131319.2574.18.camel@scientia.net> Subject: is cryptographically secure integrity checking possible with btrfs? From: Christoph Anton Mitterer To: linux-btrfs@vger.kernel.org Date: Thu, 12 Mar 2015 04:35:19 +0100 Content-Type: multipart/signed; micalg="sha-512"; protocol="application/x-pkcs7-signature"; boundary="=-2oKa5KBrFF+5Ffh1+ZnB" Mime-Version: 1.0 Sender: linux-btrfs-owner@vger.kernel.org List-ID: --=-2oKa5KBrFF+5Ffh1+ZnB Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Hey. For encryption we have dm-crypt and in principle I'm happy with having that at the block device level below the filesystem - perhaps except for any possible performance issues, especially when used with software RAID (regardless of whether MD or btrfs')[0]. But obviously integrity protection is still missing... and I guess for many people this would actually be much more interesting than encryption. Now as far as I understand btrfs, everything, data and metadata is checksummed (right now only with CRC32, but enough space would be left for something "better"). And further, these checksums are verified on each read. Are these checksums chained? I.e. when a datablock is written/changed, not only its checksum is affected, but also those of all meta-data blocks up to the super blocks? If so, one could perhaps use this like git for integrity protection. For example when unmounting a btrfs filesystem, it could print the final checksum of the superblock. The user could store this on some safe device (for the paranoid one e.g. on a USB stick that always travels along and that by coincidence also contains boot loader, kernel+initrd and the dm-crypt keys necessary to decrypt the fully encrypted system). On mount one could then specify the expected checksum for the superblock. If it differs already, then the mount should obviously fails right away (or try backup superblocks and that like, but again only use them if they match the sum). Obviously one would also need an operation mode in which btrfs dies with bells and red signs as soon as something (data or metadata) is read afterwards, which doesn't match the expected checksums. again, RAID copies, etc. could of course be tried - but if no valid copy is found, then it should assume compromise and the read operation should error out and not deliver any data at all (it may be compromised and nothing should use it). Of course people might still want to read such "compromised" blocks (e.g. when they are sure that they've only suffered from accidental data corruption and try to rescue as much as possible), but that should then require a special mount option. Well I'm not that crypto expert,... and btrfs would probably at least need more than CRC32. Unfortunately the 512bit version of Keccak wouldn't fit in, would it? ;) Cheers, Chris. [0] Does anyone know the current status of this? When I have say a btrfs RAID6 with n disks, each actually being a dm-crypt device... will this run all in one IO thread killing the performance? --=-2oKa5KBrFF+5Ffh1+ZnB Content-Type: application/x-pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgMFADCABgkqhkiG9w0BBwEAAKCCEZIw ggW/MIIDp6ADAgECAgMCOakwDQYJKoZIhvcNAQENBQAwVDEUMBIGA1UEChMLQ0FjZXJ0IEluYy4x HjAcBgNVBAsTFWh0dHA6Ly93d3cuQ0FjZXJ0Lm9yZzEcMBoGA1UEAxMTQ0FjZXJ0IENsYXNzIDMg Um9vdDAeFw0xNDA2MTIxNjM2MThaFw0xNjA2MTExNjM2MThaMHwxITAfBgNVBAMTGENocmlzdG9w aCBBbnRvbiBNaXR0ZXJlcjEkMCIGCSqGSIb3DQEJARYVY2FsZXN0eW9Ac2NpZW50aWEubmV0MTEw LwYJKoZIhvcNAQkBFiJtYWlsQGNocmlzdG9waC5hbnRvbi5taXR0ZXJlci5uYW1lMIIBIjANBgkq hkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA4phP/j9vT9dZT+k3ffHxvRWMOuzBnu5O3Fl4y2+WL7pL rfLiEhWzGXhHvjSqpt4vCNSdqy43453nnu8+hMb+uEtqSIL1AHU5eLhuDNVN9S4bt9E7nA2WKYBU 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