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If properly encrypted with an authenticated encryption mechanism then the server can be sure that the data has not been modified and has not been read. This wo

If properly encrypted with an authenticated encryption mechanism then the server can be sure that the data has not been modified and has not been read. This would allow private data to be stored. As long as the server is the only one that knows the key, then only the server can read it. An evesdropper can still use the cookies for replay attacks, but at that point they're on the connection already. It's useful for things like storing the current user session. You wouldn't want someone to be able to log in and then change their account to someone else's by modifying the user id in their cookie. Thus this information is often stored in a server-side session. With an encrypted cookie you can push this data to the client, which makes the server stateless with respect to client sessions.

shadowfiend 15y ago
(1) Modification-prevention (the changing your account to someone else's by modifying the user id situation) is provided by the HMAC, not encryption. This is why Rails session cookies are not encrypted (as far as I know), for example. (2) If someone has your cookie, they're either already on your connection or they're on your computer. (3) The only situation where this provides any security is one in which you store data in the cookie that would not be accessible to the same user through the site. I can't think of any such data in any of my experience, but I will absolutely grant that such data may exist.
- marshray 15y ago
  (1) Well, he said > If properly encrypted with an authenticated encryption mechanism (2) Being on one's connection is the default assumption of the internet security model. (3) Right, the confidentiality of the site's data from the site's user may not be critical. But if done properly it does allow the site to ensure that the data it stored has not been tampered with (except perhaps to drop it or replay it). Surely this can be useful.

shadowfiend 15y ago

(1) Modification-prevention (the changing your account to someone else's by modifying the user id situation) is provided by the HMAC, not encryption. This is why Rails session cookies are not encrypted (as far as I know), for example. (2) If someone has your cookie, they're either already on your connection or they're on your computer. (3) The only situation where this provides any security is one in which you store data in the cookie that would not be accessible to the same user through the site. I can't think of any such data in any of my experience, but I will absolutely grant that such data may exist.

marshray 15y ago
(1) Well, he said > If properly encrypted with an authenticated encryption mechanism (2) Being on one's connection is the default assumption of the internet security model. (3) Right, the confidentiality of the site's data from the site's user may not be critical. But if done properly it does allow the site to ensure that the data it stored has not been tampered with (except perhaps to drop it or replay it). Surely this can be useful.