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Can you extract domain names and usernames from the U2F devices? Like if someone wants to learn what sites he is visiting and his usernames?
by darkhorn 8y ago
Can you extract domain names and usernames from the U2F devices? Like if someone wants to learn what sites he is visiting and his usernames?
- veeti 8y agoIf the key is designed properly, no. For example, Yubikey does not store any state: https://www.yubico.com/2014/11/yubicos-u2f-key-wrapping/ https://www.yubico.com/2014/11/yubicos-u2f-key-wrapping/
- tialaramex 8y agoIn practice, no, the tokens are _way_ too dumb to remember anything like that. They're using an old cryptographic trick to appear much cleverer than they really are. During enrollment they present the server with a public key, and a magic cookie, both of which it stores. In subsequent authentication, the server sends them back the cookie, and some random data, which the token then signs to prove it still knows the private key, the server can check that because of the public key it has. But in practice the key pair never actually lives inside the token - it makes the key pair during enrollment, and the "magic cookie" was actually its private key encrypted using a secret key only the token knows. So the token has no writeable storage, just ROM and a little bit of DRAM. Some tokens might have a tiny amount of flash to e.g. store a counter or a user chosen PIN to do PIN authentication instead of a one touch auth, but they aren't storing a bunch of keys, or domain names, or email addresses.
- konschubert 8y agoThis is so cool. This feels so much like cheating that I was sure it must be flawed, but I couldn't come up with any weakness. I conviced myself that this is possible by considering the method of using a different permutation of the same key pair on each website and storing that permutation, encrypted, in a cookie. Cryptography is awesome.