Jason A. Donenfeld wrote: > I saw that jiffies addition in there and was wondering what it was all > about. It's currently added _after_ the siphash input, not before, to > keep with how the old algorithm worked. I'm not sure if this is > correct or if there's something wrong with that, as I haven't studied > how it works. If that jiffies should be part of the siphash input and > not added to the result, please tell me. Otherwise I'll keep things > how they are to avoid breaking something that seems to be working. Oh, geez, I didn't realize you didn't understand this code. Full details at https://en.wikipedia.org/wiki/TCP_sequence_prediction_attack But yes, the sequence number is supposed to be (random base) + (timestamp). In the old days before Canter & Siegel when the internet was a nice place, people just used a counter that started at boot time. But then someone observed that I can start a connection to host X, see the sequence number it gives back to me, and thereby learn the seauence number it's using on its connections to host Y. And I can use that to inject forged data into an X-to-Y connection, without ever seeing a single byte of the traffic! (If I *can* observe the traffic, of course, none of this makes the slightest difference.) So the random base was made a keyed hash of the endpoint identifiers. (Practically only the hosts matter, but generally the ports are thrown in for good measure.) That way, the ISN that host X sends to me tells me nothing about the ISN it's using to talk to host Y. Now the only way to inject forged data into the X-to-Y connection is to send 2^32 bytes, which is a little less practical. -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
