Fix 404 papers (#577)

* Update link to Interactive Horizon Mapping: Shadows for bump-mapped surfaces
* Update link to A Mathematical Theory of Cryptography (1945)

computer_graphics/README.md

@@ -28,7 +28,7 @@ This is a really great paper that is both complex and straightforward. This pape
 * [Light Propagation Volumes in CryEngine 3](http://www.crytek.com/download/Light_Propagation_Volumes.pdf)
 
 ### Bump mapping
-* [Interactive Horizon Mapping: Shadows for bump-mapped surfaces](http://research.microsoft.com/en-us/um/people/cohen/bs.pdf)
+* [Interactive Horizon Mapping: Shadows for bump-mapped surfaces](https://www.ppsloan.org/publications/bs.pdf)
 
 ### Interior mapping
 * [Interior Mapping: A new technique for rendering realistic buildings](http://www.proun-game.com/Oogst3D/CODING/InteriorMapping/InteriorMapping.pdf)

cryptography/README.md

@@ -10,7 +10,7 @@
 * [Key Reinstallation Attacks: Forcing Nonce Reuse in WPA2 (2017)](https://papers.mathyvanhoef.com/ccs2017.pdf) (Mathy Vanhoef, Frank Piessens)
 
 ## Related Works
-### [A Mathematical Theory of Cryptography (1945)](http://www.cs.bell-labs.com/who/dmr/pdfs/shannoncryptshrt.pdf) - Shannon
+### [A Mathematical Theory of Cryptography (1945)](https://www.iacr.org/museum/shannon/shannon45.pdf) - Shannon
 The original classified memo for Bell Labs that was republished in 1949 as ["Communication Theory of Secrecy Systems"](communication-theory-of-secrecy-systems.pdf).
 
 ### :scroll: [A Mathematical Theory of Communication (1948)](../information_theory/a-mathematical-theory-of-communication-1948.pdf) - Shannon