5 ms·

I heared somewhere (Some blogs comment section, I believe) that gzip actually reduces the security of HTTPS; maybe someone can confirm / explain that?

tialaramex 8y ago
Compression technologies, including gzip, obviously have the goal of making things smaller by predicting later data based on earlier data. If the later data looks more like the earlier data, the result is smaller than if it was random gibberish. Compression! If an attacker controls /some/ of this data, and would like to read /other parts/, they can abuse compression to measure whether the parts they don't know are "like" the part they control, because if they are then the compression will make the results shorter than otherwise which they can passively measure. It's not a problem to move a compressed object over a secure channel on its own, the problem arises if either you try to compress the channel which is moving objects from different origins (e.g. a cookie set by a random advertising web site and your Facebook password) or compress a composite object e.g. maybe your backups mixed with a file you downloaded from a dodgy "pirate" video site.
takeda 8y ago
In scenario when an attacker can see encrypted message (e.g. monitoring network traffic) and can affect part of the message that is being encrypted, he can use the compression to his advantage. He can for example try different inputs and observe the length of encrypted message, if with the certain input the length drops that means the given input contains string that's similar to another part of the decrypted message and the compressing algorithm did its job and used that to reduce the size. This was mentioned in 2012 when CRIME[1] (also included BEAST[2] exploit) and later BREACH[2] vulnerability (when it was considered cool to come up with cool sounding name, creating a logo and a website for specific vulnerabilities) [1] https://en.wikipedia.org/wiki/CRIME https://en.wikipedia.org/wiki/CRIME [2] https://en.wikipedia.org/wiki/Transport_Layer_Security#BEAST_attack https://en.wikipedia.org/wiki/Transport_Layer_Security#BEAST... [3] https://en.wikipedia.org/wiki/BREACH https://en.wikipedia.org/wiki/BREACH
emilfihlman 8y ago
This shouldn't be true in any sane system.

tialaramex 8y ago

Compression technologies, including gzip, obviously have the goal of making things smaller by predicting later data based on earlier data. If the later data looks more like the earlier data, the result is smaller than if it was random gibberish. Compression! If an attacker controls /some/ of this data, and would like to read /other parts/, they can abuse compression to measure whether the parts they don't know are "like" the part they control, because if they are then the compression will make the results shorter than otherwise which they can passively measure. It's not a problem to move a compressed object over a secure channel on its own, the problem arises if either you try to compress the channel which is moving objects from different origins (e.g. a cookie set by a random advertising web site and your Facebook password) or compress a composite object e.g. maybe your backups mixed with a file you downloaded from a dodgy "pirate" video site.

takeda 8y ago

In scenario when an attacker can see encrypted message (e.g. monitoring network traffic) and can affect part of the message that is being encrypted, he can use the compression to his advantage. He can for example try different inputs and observe the length of encrypted message, if with the certain input the length drops that means the given input contains string that's similar to another part of the decrypted message and the compressing algorithm did its job and used that to reduce the size. This was mentioned in 2012 when CRIME[1] (also included BEAST[2] exploit) and later BREACH[2] vulnerability (when it was considered cool to come up with cool sounding name, creating a logo and a website for specific vulnerabilities) [1] https://en.wikipedia.org/wiki/CRIME https://en.wikipedia.org/wiki/CRIME [2] https://en.wikipedia.org/wiki/Transport_Layer_Security#BEAST_attack https://en.wikipedia.org/wiki/Transport_Layer_Security#BEAST... [3] https://en.wikipedia.org/wiki/BREACH https://en.wikipedia.org/wiki/BREACH

emilfihlman 8y ago

This shouldn't be true in any sane system.