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> HTTP/2 actively discourages the use of compression for secure websites. HTTP compression (gzip, deflate, ...) has been known to compromise the SSL/TLS securit

> HTTP/2 actively discourages the use of compression for secure websites. HTTP compression (gzip, deflate, ...) has been known to compromise the SSL/TLS security in the "breach" and "CRIME" attacks. This is a patently wrong statement in an otherwise good article. There are no known security vulnerabilities with HTTP/1.x's style of compression That's because HTTP/1.x only supports compressing response bodies. During SPDY development, the same compression algorithms used for compressing HTTP responses (gzip/deflate) were applied to compress request and response headers. This is what lead to the CRIME vulnerability. The solution was to still use compression, but use a different compression scheme, HPACK, which (glossing over a ton of technical details) allows compression while avoid CRIME because it "[uses] separate compression dictionaries are used for each source of data." HTTP/2 uses HPACK. Use of TLS compression is not recommended, but that has always been a performance best practice, since TLS compression is not context aware. For the love of god, keep using compression with your websites, whether HTTP/1.x, TLS + HTTP/1.x, or HTTP/2

agwa 11y ago
> There are no known security vulnerabilities with HTTP/1.x's style of compression That's because HTTP/1.x only supports compressing response bodies You are completely wrong. The BREACH attack showed that you can be vulnerable to a compression oracle by merely compressing response bodies: http://breachattack.com/ http://breachattack.com/ > For the love of god, keep using compression with your websites, whether HTTP/1.x, TLS + HTTP/1.x, or HTTP/2 You can continue compressing files such as CSS that don't reflect any attacker-controlled content, but compression of dynamic HTML pages is likely to be insecure.
- richardwhiuk 11y ago
  It's quite depressing that we can't have both compression and encryption at the same time - text is very compressible - particularly HTML markup...
  - cesarb 11y ago
    Theoretically, you can, as long as any secrets within the response body are represented as a "literal" (that is, uncompressed) within the compressed stream. In practice, there isn't a way I know of to mark the relevant parts of the response body so that the compression, which is usually done as a separate post-processing step, will know to avoid compressing these parts of the stream. And it would be very fragile; forgetting to mark a secret as "do not compress this" would work perfectly fine but reintroduce the vulnerability.
    - derefr 11y ago
      Simply enough in HTTP2: lift out the relevant parts of the response body—turn them into separate resources and refer to them in the original object by their URL. When the client then requests those dependent objects, deliver them uncompressed. (And server-hint/push the dependent objects if you can, of course.)
  - tootie 11y ago
    You can with HTTP/2.
  - joeyespo 11y ago
    Could the order be reversed, encrypting first then compressing second? So only compress when sending over the wire?
    - Wilya 11y ago
      You could, but you wouldn't compress much. Encrypted data is supposed to look random, and as a consequence, it tends to compress very poorly.
      - joeyespo 11y ago
        Interesting. I was afraid that'd be the answer. Thanks for the reply.
- nickysielicki 11y ago
  so I have gzip compression specified in my nginx config and I use SSL for everything. Is my server vulnerable to this?
  - strommen 11y ago
    Your app is vulnerable if it includes content from the user (e.g. a GET query parameter or something from a POST request body) in the response, and includes secret info (e.g. an anti-CSRF token) in that same response.
    - nickysielicki 11y ago
      Wow, that's scary. I imagine quite a lot of people are unaware of this. I personally use SSL on my personal site just because I like the idea that readers can be sure the content is what I've sent, rather than because the information is private / sensitive. So I'm not personally concerned because this doesn't allow anyone to MITM the connection, just read it.
    - nine_k 11y ago
      I suppose that adding a small random bit into the page could defeat this known-plaintext attack?
      - strommen 11y ago
        Not really. The theory behind the attack is that if the user-specified content is equal to the secret content, it will compress more effectively and have a smaller content length. The other content on the page doesn't really matter. Adding data of random length will make the attack more difficult, but won't defeat it entirely. This is called length hiding. See http://breachattack.com/ http://breachattack.com/ for a more thorough explanation by smarter people.
        nine_k 11y ago
        The attack depends on a secret to match a user-provided string enough for the compression algorithm to notice this redundancy? A counter-measure then would be to scramble the user input in the page with a random key, and include this key into the page for de-scrambling using JavaScript. It will still efficiently compress the parts of the page which are not user-controlled.
- billyhoffman 11y ago
  ahhhh! Thank you I had completely forgotten about BREACH and was fixated on CRIME

agwa 11y ago

> There are no known security vulnerabilities with HTTP/1.x's style of compression That's because HTTP/1.x only supports compressing response bodies You are completely wrong. The BREACH attack showed that you can be vulnerable to a compression oracle by merely compressing response bodies: http://breachattack.com/ http://breachattack.com/ > For the love of god, keep using compression with your websites, whether HTTP/1.x, TLS + HTTP/1.x, or HTTP/2 You can continue compressing files such as CSS that don't reflect any attacker-controlled content, but compression of dynamic HTML pages is likely to be insecure.

richardwhiuk 11y ago
It's quite depressing that we can't have both compression and encryption at the same time - text is very compressible - particularly HTML markup...
- cesarb 11y ago
  Theoretically, you can, as long as any secrets within the response body are represented as a "literal" (that is, uncompressed) within the compressed stream. In practice, there isn't a way I know of to mark the relevant parts of the response body so that the compression, which is usually done as a separate post-processing step, will know to avoid compressing these parts of the stream. And it would be very fragile; forgetting to mark a secret as "do not compress this" would work perfectly fine but reintroduce the vulnerability.
  - derefr 11y ago
    Simply enough in HTTP2: lift out the relevant parts of the response body—turn them into separate resources and refer to them in the original object by their URL. When the client then requests those dependent objects, deliver them uncompressed. (And server-hint/push the dependent objects if you can, of course.)
- tootie 11y ago
  You can with HTTP/2.
- joeyespo 11y ago
  Could the order be reversed, encrypting first then compressing second? So only compress when sending over the wire?
  - Wilya 11y ago
    You could, but you wouldn't compress much. Encrypted data is supposed to look random, and as a consequence, it tends to compress very poorly.
    - joeyespo 11y ago
      Interesting. I was afraid that'd be the answer. Thanks for the reply.
nickysielicki 11y ago
so I have gzip compression specified in my nginx config and I use SSL for everything. Is my server vulnerable to this?
- strommen 11y ago
  Your app is vulnerable if it includes content from the user (e.g. a GET query parameter or something from a POST request body) in the response, and includes secret info (e.g. an anti-CSRF token) in that same response.
  - nickysielicki 11y ago
    Wow, that's scary. I imagine quite a lot of people are unaware of this. I personally use SSL on my personal site just because I like the idea that readers can be sure the content is what I've sent, rather than because the information is private / sensitive. So I'm not personally concerned because this doesn't allow anyone to MITM the connection, just read it.
  - nine_k 11y ago
    I suppose that adding a small random bit into the page could defeat this known-plaintext attack?
    - strommen 11y ago
      Not really. The theory behind the attack is that if the user-specified content is equal to the secret content, it will compress more effectively and have a smaller content length. The other content on the page doesn't really matter. Adding data of random length will make the attack more difficult, but won't defeat it entirely. This is called length hiding. See http://breachattack.com/ http://breachattack.com/ for a more thorough explanation by smarter people.
      - nine_k 11y ago
        The attack depends on a secret to match a user-provided string enough for the compression algorithm to notice this redundancy? A counter-measure then would be to scramble the user input in the page with a random key, and include this key into the page for de-scrambling using JavaScript. It will still efficiently compress the parts of the page which are not user-controlled.
billyhoffman 11y ago
ahhhh! Thank you I had completely forgotten about BREACH and was fixated on CRIME