There is a number of really quite good applied maths courses on youtube (roughly in this order from each group):
MIT 18.06, 18.085, 18.086, 6.262, 6.450
Stanford EE263, EE364A, EE261
Profs Strang, Boyd and Gallager are quite a bit better with maths than the typical engineering lecturer, even though their courses are not exactly at the level of Rudin, Breiman et al.
It's not comprehensive by any means, and you probably need to know at least calculus to be ready for most of this, but it covers some pretty cool stuff, including RSA.
MIT 18.06, 18.085, 18.086, 6.262, 6.450
Stanford EE263, EE364A, EE261
Profs Strang, Boyd and Gallager are quite a bit better with maths than the typical engineering lecturer, even though their courses are not exactly at the level of Rudin, Breiman et al.