- From: James M Snell <jasnell@gmail.com>
- Date: Mon, 14 Jan 2013 23:47:09 -0800
- To: Roberto Peon <grmocg@gmail.com>
- Cc: HTTP Working Group <ietf-http-wg@w3.org>
- Message-ID: <CABP7Rbe-WEy3M+kXShwwngbB-wUhQkZjS+9onXGynwsxkDLnaQ@mail.gmail.com>
Oh yes, I fully understand... like I said, this is not intended to make it impossible, just harder, and the idea is to throw some variations on the table so we can get a good comparison of the options. For this particular variation, there are only two buckets. I tested with three and the compression efficiency drops off by an order of magnitude. With two buckets we are able to maintain a compression ratio roughly on par with http1-gzip and consistently better than delta. But, like you said, it's not a "fix".. it just makes attacks like CRIME harder to execute by some degree. On Mon, Jan 14, 2013 at 9:34 PM, Roberto Peon <grmocg@gmail.com> wrote: > I'm trying to express, I guess, that as the number of buckets goes up, the > compression becomes correspondingly less effective, and it has a limited > (eventually constant) security benefit after enough requests. > > I believe this ends up being a binomial distribution thus, for k buckets > and k requests I believe that we end with a probability of hitting a bucket > that does not have the sensitive data of only 1/e (increasing security by > roughly 36%) while decreasing compression effectiveness by strictly worse > than 54% (i.e. 1-1/e at the limit). > > The attackers are better math geeks than I am. This may explain my > wariness to play with any kind of stream compressor and make assertions > about safety :) > -=R > > > On Mon, Jan 14, 2013 at 7:07 PM, James M Snell <jasnell@gmail.com> wrote: > >> The randomization is not intended to make reverse engineering impossible, >> just a large degree more difficult (and potentially more impractical). Used >> in combination with other strategies -- such as moving away from the use of >> unauthenticated session ids in cookies -- it could prove effective enough >> to get the job done. >> >> >> On Mon, Jan 14, 2013 at 7:01 PM, Roberto Peon <grmocg@gmail.com> wrote: >> >>> An attacker would run its experiment some increased number of times and >>> still get information about what is in the context, assuming i am >>> understanding it correctly. :/ >>> >>> -=R >>> On Jan 14, 2013 5:33 PM, "James M Snell" <jasnell@gmail.com> wrote: >>> >>> Just continuing the investigation on various compression strategies. I >>> spent part of the day going through delta to make sure I understand it and >>> how it compares with bohe... I'll have some additional thoughts (and >>> concerns) with regards to that later on... The other half of the day has >>> been spent with various other bohe variations. Late in the after I hit upon >>> a particularly interesting variation... I've checked it in here: >>> https://github.com/jasnell/compression-test/tree/master/compressor/bohe4 >>> >>> This variation encodes headers and randomly assigns them to one of two >>> separate buckets. Those are then randomly ordered and compressed using two >>> separate compressor instances within the header block... >>> >>> # +-------------+--------------------------+ >>> # | num_headers | block 1 len (4 bytes) | >>> # +-------------+--------------------------+ >>> # | compressed header block 1 | >>> # +----------------------------+-----------+ >>> # | block 2 len (4 bytes) | | >>> # +----------------------------+ | >>> # | compressed header block 2 | >>> # +----------------------------+-----------+ >>> >>> Because of the randomization, there is no way of determining in advance >>> which block any individual piece of data will land... making it much harder >>> for an attacker to use the compression ratio to reverse engineer any >>> particular value... every time the information is sent, it can be in a >>> different location. You can take the exact same request and encode it >>> multiple times and end up with a different message size every time (up to a >>> given limit, of course). >>> >>> Some numbers from various test runs... note how bohe4 produces variable >>> compression ratios given identical input. >>> >>> ./compare_compressors.py -c bohe -c bohe4 -c delta -t >>> /Users/james/git/http_samples/mnot/wikipedia.org.har >>> 408 req messages processed >>> compressed | ratio min max std >>> req bohe 10,784 | 0.13 0.05 0.65 0.07 >>> req bohe4 13,496 | 0.16 0.05 0.69 0.08 >>> req delta 16,725 | 0.20 0.04 0.72 0.09 >>> req http1 84,388 | 1.00 1.00 1.00 0.00 >>> >>> 408 res messages processed >>> compressed | ratio min max std >>> res bohe 19,882 | 0.25 0.06 0.58 0.10 >>> res bohe4 20,610 | 0.26 0.09 0.63 0.09 >>> res delta 24,523 | 0.30 0.04 0.60 0.12 >>> res http1 80,613 | 1.00 1.00 1.00 0.00 >>> >>> ./compare_compressors.py -c bohe -c bohe4 -c delta -t >>> /Users/james/git/http_samples/mnot/wikipedia.org.har >>> 408 req messages processed >>> compressed | ratio min max std >>> req bohe 10,784 | 0.13 0.05 0.65 0.07 >>> req bohe4 13,820 | 0.16 0.07 0.67 0.08 >>> req delta 16,725 | 0.20 0.04 0.72 0.09 >>> req http1 84,388 | 1.00 1.00 1.00 0.00 >>> >>> 408 res messages processed >>> compressed | ratio min max std >>> res bohe 19,882 | 0.25 0.06 0.58 0.10 >>> res bohe4 21,644 | 0.27 0.09 0.61 0.09 >>> res delta 24,523 | 0.30 0.04 0.60 0.12 >>> res http1 80,613 | 1.00 1.00 1.00 0.00 >>> >>> Again, this is just intended as fodder for discussion right now. I'll >>> have some comments specifically on delta encoding tomorrow sometime. >>> >>> - James >>> >>> >>> On Thu, Jan 10, 2013 at 11:08 AM, James M Snell <jasnell@gmail.com>wrote: >>> >>>> I have an initial bohe implementation for the compression tests... it's >>>> very preliminary and uses the same gzip compression as the current spdy3. >>>> I'm going to be playing around with the delta compression mechanism as well >>>> and see how much of an impact that has. Initial results are very promising >>>> but I haven't done much debugging yet. Just wanted folks to know that this >>>> work was underway... >>>> >>>> https://github.com/jasnell/compression-test/tree/master/compressor/bohe >>>> >>>> Some test runs.... >>>> >>>> ./compare_compressors.py -c bohe -c spdy3 -c delta >>>> ../http_samples/mnot/amazon.com.har >>>> 732 req messages processed >>>> compressed | ratio min max std >>>> req bohe 26,122 | 0.13 0.04 0.70 0.08 >>>> req delta 33,955 | 0.17 0.02 0.71 0.09 >>>> req http1 195,386 | 1.00 1.00 1.00 0.00 >>>> req spdy3 27,238 | 0.14 0.04 0.71 0.08 >>>> >>>> 732 res messages processed >>>> compressed | ratio min max std >>>> res bohe 39,628 | 0.25 0.04 0.66 0.07 >>>> res delta 44,499 | 0.28 0.02 0.65 0.09 >>>> res http1 159,968 | 1.00 1.00 1.00 0.00 >>>> res spdy3 41,325 | 0.26 0.04 0.67 0.08 >>>> >>>> >>>> ./compare_compressors.py -c bohe -c spdy3 -c delta >>>> ../http_samples/mnot/craigslist.org.har >>>> 66 req messages processed >>>> compressed | ratio min max std >>>> req bohe 1,948 | 0.15 0.06 0.73 0.11 >>>> req delta 2,036 | 0.16 0.07 0.71 0.11 >>>> req http1 12,894 | 1.00 1.00 1.00 0.00 >>>> req spdy3 2,016 | 0.16 0.07 0.75 0.11 >>>> >>>> 66 res messages processed >>>> compressed | ratio min max std >>>> res bohe 1,786 | 0.18 0.07 0.77 0.13 >>>> res delta 2,858 | 0.28 0.08 0.69 0.12 >>>> res http1 10,147 | 1.00 1.00 1.00 0.00 >>>> res spdy3 1,869 | 0.18 0.09 0.78 0.13 >>>> >>>> >>>> ./compare_compressors.py -c bohe -c spdy3 -c delta >>>> ../http_samples/mnot/flickr.com.har >>>> 438 req messages processed >>>> compressed | ratio min max std >>>> req bohe 11,988 | 0.10 0.02 0.69 0.07 >>>> req delta 26,372 | 0.22 0.01 0.71 0.14 >>>> req http1 121,854 | 1.00 1.00 1.00 0.00 >>>> req spdy3 12,550 | 0.10 0.02 0.71 0.07 >>>> >>>> 438 res messages processed >>>> compressed | ratio min max std >>>> res bohe 13,073 | 0.09 0.05 0.66 0.06 >>>> res delta 25,236 | 0.18 0.02 0.70 0.11 >>>> res http1 140,457 | 1.00 1.00 1.00 0.00 >>>> res spdy3 14,142 | 0.10 0.05 0.66 0.06 >>>> >>>> >>>> ./compare_compressors.py -c bohe -c spdy3 -c delta >>>> ../http_samples/mnot/facebook.com.har >>>> 234 req messages processed >>>> compressed | ratio min max std >>>> req bohe 6,091 | 0.15 0.06 0.78 0.07 >>>> req delta 7,800 | 0.19 0.02 0.70 0.07 >>>> req http1 41,980 | 1.00 1.00 1.00 0.00 >>>> req spdy3 6,301 | 0.15 0.06 0.77 0.07 >>>> >>>> 234 res messages processed >>>> compressed | ratio min max std >>>> res bohe 9,458 | 0.23 0.07 0.68 0.07 >>>> res delta 12,045 | 0.30 0.13 0.60 0.08 >>>> res http1 40,252 | 1.00 1.00 1.00 0.00 >>>> res spdy3 9,788 | 0.24 0.07 0.69 0.07 >>>> >>>> >>>> >>>> >>>> >>> >> >
Received on Tuesday, 15 January 2013 07:48:11 UTC