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.. in the systems with non-trusted server
This new functionality can be useful in various cloud technologies.
It is implemented via a special encryption/crypt translator,which
works on the client side and performs encryption and authentication;
1. Class of supported algorithms
The crypt translator can support any atomic symmetric block cipher
algorithms (which require to pad plain/cipher text before performing
encryption/decryption transform (see glossary in atom.c for
definitions). In particular, it can support algorithms with the EOF
issue (which require to pad the end of file by extra-data).
Crypt translator performs translations
user -> (offset, size) -> (aligned-offset, padded-size) ->server
(and backward), and resolves individual FOPs (write(), truncate(),
etc) to read-modify-write sequences.
A volume can contain files encrypted by different algorithms of the
mentioned class. To change some option value just reconfigure the
volume.
Currently only one algorithm is supported: AES_XTS.
Example of algorithms, which can not be supported by the crypt
translator:
1. Asymmetric block cipher algorithms, which inflate data, e.g. RSA;
2. Symmetric block cipher algorithms with inline MACs for data
authentication.
2. Implementation notes.
a) Atomic algorithms
Since any process in a stackable file system manipulates with local
data (which can be obsoleted by local data of another process), any
atomic cipher algorithm without proper support can lead to non-POSIX
behavior. To resolve the "collisions" we introduce locks: before
performing FOP->read(), FOP->write(), etc. the process should first
lock the file.
b) Algorithms with EOF issue
Such algorithms require to pad the end of file with some extra-data.
Without proper support this will result in losing information about
real file size. Keeping a track of real file size is a responsibility
of the crypt translator. A special extended attribute with the name
"trusted.glusterfs.crypt.att.size" is used for this purpose. All files
contained in bricks of encrypted volume do have "padded" sizes.
3. Non-trusted servers and
Metadata authentication
We assume that server, where user's data is stored on is non-trusted.
It means that the server can be subjected to various attacks directed
to reveal user's encrypted personal data. We provide protection
against such attacks.
Every encrypted file has specific private attributes (cipher algorithm
id, atom size, etc), which are packed to a string (so-called "format
string") and stored as a special extended attribute with the name
"trusted.glusterfs.crypt.att.cfmt". We protect the string from
tampering. This protection is mandatory, hardcoded and is always on.
Without such protection various attacks (based on extending the scope
of per-file secret keys) are possible.
Our authentication method has been developed in tight collaboration
with Red Hat security team and is implemented as "metadata loader of
version 1" (see file metadata.c). This method is NIST-compliant and is
based on checking 8-byte per-hardlink MACs created(updated) by
FOP->create(), FOP->link(), FOP->unlink(), FOP->rename() by the
following unique entities:
. file (hardlink) name;
. verified file's object id (gfid).
Every time, before manipulating with a file, we check it's MACs at
FOP->open() time. Some FOPs don't require a file to be opened (e.g.
FOP->truncate()). In such cases the crypt translator opens the file
mandatory.
4. Generating keys
Unique per-file keys are derived by NIST-compliant methods from the
a) parent key;
b) unique verified object-id of the file (gfid);
Per-volume master key, provided by user at mount time is in the root
of this "tree of keys".
Those keys are used to:
1) encrypt/decrypt file data;
2) encrypt/decrypt file metadata;
3) create per-file and per-link MACs for metadata authentication.
5. Instructions
Getting started with crypt translator
Example:
1) Create a volume "myvol" and enable encryption:
# gluster volume create myvol pepelac:/vols/xvol
# gluster volume set myvol encryption on
2) Set location (absolute pathname) of your master key:
# gluster volume set myvol encryption.master-key /home/me/mykey
3) Set other options to override default options, if needed.
Start the volume.
4) On the client side make sure that the file /home/me/mykey exists
and contains proper per-volume master key (that is 256-bit AES
key). This key has to be in hex form, i.e. should be represented
by 64 symbols from the set {'0', ..., '9', 'a', ..., 'f'}.
The key should start at the beginning of the file. All symbols at
offsets >= 64 are ignored.
5) Mount the volume "myvol" on the client side:
# glusterfs --volfile-server=pepelac --volfile-id=myvol /mnt
After successful mount the file which contains master key may be
removed. NOTE: Keeping the master key between mount sessions is in
user's competence.
**********************************************************************
WARNING! Losing the master key will make content of all regular files
inaccessible. Mount with improper master key allows to access content
of directories: file names are not encrypted.
**********************************************************************
6. Options of crypt translator
1) "master-key": specifies location (absolute pathname) of the file
which contains per-volume master key. There is no default location
for master key.
2) "data-key-size": specifies size of per-file key for data encryption
Possible values:
. "256" default value
. "512"
3) "block-size": specifies atom size. Possible values:
. "512"
. "1024"
. "2048"
. "4096" default value;
7. Test cases
Any workload, which involves the following file operations:
->create();
->open();
->readv();
->writev();
->truncate();
->ftruncate();
->link();
->unlink();
->rename();
->readdirp().
8. TODOs:
1) Currently size of IOs issued by crypt translator is restricted
by block_size (4K by default). We can use larger IOs to improve
performance.
Change-Id: I2601fe95c5c4dc5b22308a53d0cbdc071d5e5cee
BUG: 1030058
Signed-off-by: Edward Shishkin <edward@redhat.com>
Signed-off-by: Anand Avati <avati@redhat.com>
Reviewed-on: http://review.gluster.org/4667
Tested-by: Gluster Build System <jenkins@build.gluster.com>
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