> Think about how many sets of constants can be generated in a nondescript way
One example of this is the BADA55 curves[0]:
> The name "BADA55" (pronounced "bad-ass") is explained by the appearance of the string BADA55 near the beginning of each BADA55 curve. This string is underlined in the Sage scripts above
> We actually chose this string in advance and then manipulated the curve choices to produce this string. The BADA55-VR curves illustrate the fact that, as pointed out by Scott in 1999, "verifiably random" curves do not stop the attacker from generating a curve with a one-in-a-million weakness. The BADA55-VPR curves illustrate the fact that "verifiably pseudorandom" curves with "systematic" seeds generated from "nothing-up-my-sleeve numbers" also do not stop the attacker from generating a curve with a one-in-a-million weakness.
It allows twitter to easily track which links you're clicking on, which some might consider to be a violation of privacy.
On mobile, t.co makes it so that you end up always launching a browser before launching the appropriate application (i.e. YouTube)
When you copy and paste and send a link to someone, they have no (easy) way of knowing what you're sending them without description or visiting, and it gives Twitter a mechanism for tracking who you send the link to. (One could posit a "malicious" tracking twitter where they serve up t.co links to people which are dependent on the logged in user to track that user's social network... fortunately I don't think this has happened yet.)
One example of this is the BADA55 curves[0]:
> The name "BADA55" (pronounced "bad-ass") is explained by the appearance of the string BADA55 near the beginning of each BADA55 curve. This string is underlined in the Sage scripts above
> We actually chose this string in advance and then manipulated the curve choices to produce this string. The BADA55-VR curves illustrate the fact that, as pointed out by Scott in 1999, "verifiably random" curves do not stop the attacker from generating a curve with a one-in-a-million weakness. The BADA55-VPR curves illustrate the fact that "verifiably pseudorandom" curves with "systematic" seeds generated from "nothing-up-my-sleeve numbers" also do not stop the attacker from generating a curve with a one-in-a-million weakness.
[0] http://safecurves.cr.yp.to/bada55.html