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> oh wow, Signed Exchanges are worse than AMP! > "make sure you are visiting mybanksite.com" is no longer safe. Sounds like you don't trust public key based c

by danans 7y ago

> oh wow, Signed Exchanges are worse than AMP! > "make sure you are visiting mybanksite.com" is no longer safe. Sounds like you don't trust public key based content signing. This is just broadening public key based signatures beyond the domain to include the domain and the content itself, and using signing to make the authenticity of the content independent of the physical infrastructure that served it. That' what's being used here to verify authenticity of content's source, just like PGP/GPG does for signed emails. That's a far stronger guarantee than "the data is authentic because it came IP address range X purchased by company Y". In fact, without a such signature, there is no guarantee that just because a piece of content came from a particular server/datacenter, that it is authentic. With signed exchanges, the chain of authenticity is pushed all the way back to the website's content creators - it doesn't stop at the web server. Also, this can't be phished unless you break the the content signing algorithms, and if that happens ... we all have bigger problems.

buboard 7y ago
first, it breaks the URL specification, as the "host" is no longer a host. it breaks user's expectation of one of the VERY FEW things that everyday users understand about the internet. one may manage to upload an html file to the bank's server and serve a -signed- page that google amp will cache, and then use it to phish customers from within the bank's domain. Or just use a stolen key to make thousands of such pages before the bank finds out. I think , contrary to what you say, it's a brand new, major attack surface.
- Ajedi32 7y ago
  > one may manage to upload an html file to the bank's server and serve a -signed- page that google amp will cache Only if you have the bank's private key, and the ability to serve arbitrary content from the bank's domain. In which case... yeah, I don't see how the signed exchanges standard makes that problem significantly worse.
  - buboard 7y ago
    i don't know what's the max expiration for amp's cache, but i could set a really-long expiration date on the file and remove it from the server without the bank ever knowing it existed. SGX don't even require an upload - one disgruntled employee could do the same with a stolen key. Nobody benefits from this shit than google. Do we really need more attack surfaces?
- danans 7y ago
  > first, it breaks the URL specification, as the "host" is no longer a host. By this definition, "host" hasn't been a host in a long time, since the time it was possible to route DNS traffic to multiple IP addresses, possibly in different datacenters. > it breaks user's expectation of one of the VERY FEW things that everyday users understand about the internet. How is signing content directly less authentic than signing only at the web server? Signing content directly at the time of publishing ensures that it was created using the private keys of the entity in question, regardless of the delivery mechanism for the content. > one may manage to upload an html file to the bank's server and serve a -signed- page that google amp will cache, Signed content exchanges specifically limit that by putting the content signing step at the content creator level, not the web server level. Unless you steal the content creator's private keys, you can't represent your content as theirs.
  - buboard 7y ago
    > "host" hasn't been a host in a long time, Does SXG make this better or worse? > ensures that it was created using the private keys signing at the server ensures that it was created using the key AND served from a host they control. How is that not better? > you can't represent your content wouldn't the server sign all http responses by default? all you would need to do is upload a file
    - danans 7y ago
      > wouldn't the server sign all http responses by default? all you would need to do is upload a file No, the content has to be signed when it is created, in the content management system or similar content creation tool, not when the server sends it. The content management system itself must have strong controls on it (ACLs, controlled user accounts, protected private keys stored only on encrypted and access controlled media, regular audits, etc). Basically the server itself is no longer trusted as the arbiter of content authenticity, the actual content creator is. Concretely, when the editor at a publication approves an article after reviewing it, it is signed for delivery at the moment of publication, not at the moment that the request is served.
- jsnell 7y ago
  > first, it breaks the URL specification, as the "host" is no longer a host. Really, how so? RFC 3986 goes out of it's way to make clear that the "host" component doesn't mean DNS, and doesn't even have to denote a host. "In other cases, the data within the host component identifies a registered name that has nothing to do with an Internet host." "A URI resolution implementation might use DNS, host tables, yellow pages, NetInfo, WINS, or any other system for lookup of registered names." > it breaks user's expectation of one of the FEW things that everyday users understand about the internet. What, exactly and concretely, is that expectation? > one may manage to upload an html file to the bank's server and serve a -signed- page that google amp will cache, and then use it to phish customers from within the bank's domain. If the attacker can upload arbitrary pages to the bank's website, just why would they need signed exchanges? They've already got their phishing page on the correct domain.
  - buboard 7y ago
    > RFC 3986 goes out of it's way the RFC uses the word "host" and not "signer". It also says that the "host" is intented to be looked up in some service registry, and there is no such thing for arbitrary signers. > exactly and concretely, is that expectation One of the common security advice banks used to give is "check your browser address that you are in our server" > just why would they need signed exchanges with signed exchanges they can fool amp to cache the page long after it has been deleted from the server
    - danans 7y ago
      > One of the common security advice banks used to give is "check your browser address that you are in our server" " in our server" is a simplification of the technical explanation: "signed by our computers using our private keys before delivery to you". That is still maintained in the case of signed content exchange, but instead the transport function is provided by a different server. It's not much different than, i.e. signing a compiled app with your private keys before uploading it to an app store. Such apps also use hosts to identify themselves and their content, even though they are delivered via app-store mechanisms.
kortilla 7y ago
I’m not sure you understand the purpose of https. Ensuring integrity of the document served by the server is only one small piece of it. The other critical components are: encryption so middleboxes can’t see what you’re looking at guarantee (via the PKI) that the server you’re about to send your banking credentials to is using a cert that belongs to the domain name in the address bar that you trust sending your credentials to.
- danans 7y ago
  > encryption so middleboxes can’t see what you’re looking at > guarantee (via the PKI) that the server you’re about to send your banking credentials to is using a cert that belongs to the domain name in the address bar that you trust sending your credentials to. The purpose of SXG is to allow publisher signing of edge-cache accelerated public content - i.e. it's read-only - not to encrypt private information like credentials in transport. Https still handles encrypted transport independently of SXG. Also, why or how would someone create a system that accepted private info or credentials via signed SXG anyways? There's literally no mechanism in it to achieve that. If you tried to build a password entry field for your bank website and distributed it via SXG, it wouldn't even work in the first place.
  - buboard 7y ago
    > The purpose of SXG is to allow publisher signing of edge-cache accelerated public content Is there a rule that SXG content can't contain forms or sth?
    - danans 7y ago
      No, you can distribute whatever content you want. But the content distribution network can't listen for posts from those forms when the content is rendered. SXG doesn't answer DNS requests for your domain. It only says that a particular piece of content has been signed using private keys that have been registered with the displayed host. That's it. In fact, you don't even need a CDN or DNS to distribute SXG content. You could distribute it via USB drives, or code flags, USB drives attached to messenger pigeons, whatever. The point is that authenticity of the origin of the content is completely independent of how the content got to you. When that SXG content, however it is distributed, is rendered, the browser represents that content as originating from your domain, which is in fact exactly where it originated.
efreak 7y ago
I hadn't realized the content was actually signed; I assumed we were simply trusting Google to send us the content they said they were sending (much like we do when using the Google cache). I'm curious now: would it be possible to use use the content/markup intended for use by the amp cache to view a static/unscripted/readable version of the page's main content? If so, why hasn't anyone built a browser extension to do so? On a broader note, this also sounds like it could be used to allow caching proxies to work with https; you'd lose the privacy, but you'd gain from being able to cache content on local network if the browser only had to verify the content, and you trusted the cache not to spy on you.
- danans 7y ago
  > I'm curious now: would it be possible to use use the content/markup intended for use by the amp cache to view a static/unscripted/readable version of the page's main content? If so, why hasn't anyone built a browser extension to do so? If the goal is to get around the AMP CDN, you don't even need to read the main page content. The AMP URL contains the original source URL itself [1]. The extension you are describing would just need to capture all requests with the prefix https://www.google.com/amp https://www.google.com/amp (or whatever CDN you are trying to get around), parse out the original URL, and then fetch it, and do what you will with it. If the goal is to disable scripting on the AMP CDN delivered content, first note that AMP pages can't contain page-author-written JS [2], and any implicit JS has to run async. But if that's insufficient, you can disable JS in the browser altogether, which would disable it in the loaded AMP content. You could also try to parse out the main content from your extension from the AMP page if you know from the URL that it's an AMP page. Because AMP's forces relative terseness and simplicity of HTML content, it is probably easier to parse than original page's content. Obviously that won't generalize easily given the large variety of possible of content representations, but you stand a better chance of achieving this with AMP content than the original content. And if you generalize it enough, you will end up with one component of a web crawl / indexing system in an extension ;) 1. https://blog.amp.dev/2017/02/06/whats-in-an-amp-url https://blog.amp.dev/2017/02/06/whats-in-an-amp-url 2. https://amp.dev/about/how-amp-works/ https://amp.dev/about/how-amp-works/

by danans 7y ago

buboard 7y ago

first, it breaks the URL specification, as the "host" is no longer a host. it breaks user's expectation of one of the VERY FEW things that everyday users understand about the internet. one may manage to upload an html file to the bank's server and serve a -signed- page that google amp will cache, and then use it to phish customers from within the bank's domain. Or just use a stolen key to make thousands of such pages before the bank finds out. I think , contrary to what you say, it's a brand new, major attack surface.

Ajedi32 7y ago
> one may manage to upload an html file to the bank's server and serve a -signed- page that google amp will cache Only if you have the bank's private key, and the ability to serve arbitrary content from the bank's domain. In which case... yeah, I don't see how the signed exchanges standard makes that problem significantly worse.
- buboard 7y ago
  i don't know what's the max expiration for amp's cache, but i could set a really-long expiration date on the file and remove it from the server without the bank ever knowing it existed. SGX don't even require an upload - one disgruntled employee could do the same with a stolen key. Nobody benefits from this shit than google. Do we really need more attack surfaces?
danans 7y ago
> first, it breaks the URL specification, as the "host" is no longer a host. By this definition, "host" hasn't been a host in a long time, since the time it was possible to route DNS traffic to multiple IP addresses, possibly in different datacenters. > it breaks user's expectation of one of the VERY FEW things that everyday users understand about the internet. How is signing content directly less authentic than signing only at the web server? Signing content directly at the time of publishing ensures that it was created using the private keys of the entity in question, regardless of the delivery mechanism for the content. > one may manage to upload an html file to the bank's server and serve a -signed- page that google amp will cache, Signed content exchanges specifically limit that by putting the content signing step at the content creator level, not the web server level. Unless you steal the content creator's private keys, you can't represent your content as theirs.
- buboard 7y ago
  > "host" hasn't been a host in a long time, Does SXG make this better or worse? > ensures that it was created using the private keys signing at the server ensures that it was created using the key AND served from a host they control. How is that not better? > you can't represent your content wouldn't the server sign all http responses by default? all you would need to do is upload a file
  - danans 7y ago
    > wouldn't the server sign all http responses by default? all you would need to do is upload a file No, the content has to be signed when it is created, in the content management system or similar content creation tool, not when the server sends it. The content management system itself must have strong controls on it (ACLs, controlled user accounts, protected private keys stored only on encrypted and access controlled media, regular audits, etc). Basically the server itself is no longer trusted as the arbiter of content authenticity, the actual content creator is. Concretely, when the editor at a publication approves an article after reviewing it, it is signed for delivery at the moment of publication, not at the moment that the request is served.
jsnell 7y ago
> first, it breaks the URL specification, as the "host" is no longer a host. Really, how so? RFC 3986 goes out of it's way to make clear that the "host" component doesn't mean DNS, and doesn't even have to denote a host. "In other cases, the data within the host component identifies a registered name that has nothing to do with an Internet host." "A URI resolution implementation might use DNS, host tables, yellow pages, NetInfo, WINS, or any other system for lookup of registered names." > it breaks user's expectation of one of the FEW things that everyday users understand about the internet. What, exactly and concretely, is that expectation? > one may manage to upload an html file to the bank's server and serve a -signed- page that google amp will cache, and then use it to phish customers from within the bank's domain. If the attacker can upload arbitrary pages to the bank's website, just why would they need signed exchanges? They've already got their phishing page on the correct domain.
- buboard 7y ago
  > RFC 3986 goes out of it's way the RFC uses the word "host" and not "signer". It also says that the "host" is intented to be looked up in some service registry, and there is no such thing for arbitrary signers. > exactly and concretely, is that expectation One of the common security advice banks used to give is "check your browser address that you are in our server" > just why would they need signed exchanges with signed exchanges they can fool amp to cache the page long after it has been deleted from the server
  - danans 7y ago
    > One of the common security advice banks used to give is "check your browser address that you are in our server" " in our server" is a simplification of the technical explanation: "signed by our computers using our private keys before delivery to you". That is still maintained in the case of signed content exchange, but instead the transport function is provided by a different server. It's not much different than, i.e. signing a compiled app with your private keys before uploading it to an app store. Such apps also use hosts to identify themselves and their content, even though they are delivered via app-store mechanisms.

kortilla 7y ago

I’m not sure you understand the purpose of https. Ensuring integrity of the document served by the server is only one small piece of it. The other critical components are: encryption so middleboxes can’t see what you’re looking at guarantee (via the PKI) that the server you’re about to send your banking credentials to is using a cert that belongs to the domain name in the address bar that you trust sending your credentials to.

danans 7y ago
> encryption so middleboxes can’t see what you’re looking at > guarantee (via the PKI) that the server you’re about to send your banking credentials to is using a cert that belongs to the domain name in the address bar that you trust sending your credentials to. The purpose of SXG is to allow publisher signing of edge-cache accelerated public content - i.e. it's read-only - not to encrypt private information like credentials in transport. Https still handles encrypted transport independently of SXG. Also, why or how would someone create a system that accepted private info or credentials via signed SXG anyways? There's literally no mechanism in it to achieve that. If you tried to build a password entry field for your bank website and distributed it via SXG, it wouldn't even work in the first place.
- buboard 7y ago
  > The purpose of SXG is to allow publisher signing of edge-cache accelerated public content Is there a rule that SXG content can't contain forms or sth?
  - danans 7y ago
    No, you can distribute whatever content you want. But the content distribution network can't listen for posts from those forms when the content is rendered. SXG doesn't answer DNS requests for your domain. It only says that a particular piece of content has been signed using private keys that have been registered with the displayed host. That's it. In fact, you don't even need a CDN or DNS to distribute SXG content. You could distribute it via USB drives, or code flags, USB drives attached to messenger pigeons, whatever. The point is that authenticity of the origin of the content is completely independent of how the content got to you. When that SXG content, however it is distributed, is rendered, the browser represents that content as originating from your domain, which is in fact exactly where it originated.

efreak 7y ago

I hadn't realized the content was actually signed; I assumed we were simply trusting Google to send us the content they said they were sending (much like we do when using the Google cache). I'm curious now: would it be possible to use use the content/markup intended for use by the amp cache to view a static/unscripted/readable version of the page's main content? If so, why hasn't anyone built a browser extension to do so? On a broader note, this also sounds like it could be used to allow caching proxies to work with https; you'd lose the privacy, but you'd gain from being able to cache content on local network if the browser only had to verify the content, and you trusted the cache not to spy on you.

danans 7y ago
> I'm curious now: would it be possible to use use the content/markup intended for use by the amp cache to view a static/unscripted/readable version of the page's main content? If so, why hasn't anyone built a browser extension to do so? If the goal is to get around the AMP CDN, you don't even need to read the main page content. The AMP URL contains the original source URL itself [1]. The extension you are describing would just need to capture all requests with the prefix https://www.google.com/amp https://www.google.com/amp (or whatever CDN you are trying to get around), parse out the original URL, and then fetch it, and do what you will with it. If the goal is to disable scripting on the AMP CDN delivered content, first note that AMP pages can't contain page-author-written JS [2], and any implicit JS has to run async. But if that's insufficient, you can disable JS in the browser altogether, which would disable it in the loaded AMP content. You could also try to parse out the main content from your extension from the AMP page if you know from the URL that it's an AMP page. Because AMP's forces relative terseness and simplicity of HTML content, it is probably easier to parse than original page's content. Obviously that won't generalize easily given the large variety of possible of content representations, but you stand a better chance of achieving this with AMP content than the original content. And if you generalize it enough, you will end up with one component of a web crawl / indexing system in an extension ;) 1. https://blog.amp.dev/2017/02/06/whats-in-an-amp-url https://blog.amp.dev/2017/02/06/whats-in-an-amp-url 2. https://amp.dev/about/how-amp-works/ https://amp.dev/about/how-amp-works/