Adds the README

Author: Denis Diemert

README.md

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+## upb.crypto.math
+
+upb.crypto.math is a library providing a number of mathematical tools needed in many cryptographic applications.
+
+These include:
+
+* Elliptic curve groups with pairings
+    * Type 1:
+        * Supersingular Curve with Tate pairing
+    * Type 3: 
+        * Barreto-Naehrig
+* Hashing
+    * SHA-256
+    * SHA-512
+* Mathematical structures:
+    * Ring of integers modulo n
+    * Ring of polynomials
+    
+## Example Code
+    
+As a starting point, we provide exemplary code of common tasks.
+
+##### Setting up a Type 3 Bilinear Group
+
+Given a security parameter `securityParameter`, we can set up a type 3 bilinear group using this library as follows:
+
+```java
+BilinearGroupFactory fac = new BilinearGroupFactory(securityParameter);
+fac.setRequirements(BilinearGroup.Type.TYPE_3);
+BilinearGroup group = fac.createBilinearGroup();
+``` 
+
+This chooses a type 3 bilinear group from predefined ones. Alternatively, the library enables it to register new groups by defining a `BilinearGroupProvider`.
+
+##### Register your own Bilinear Group Implementation
+
+Suppose you have your own implementation of a type 3 bilinear group and you want to use it in our library. To do so, you only need write a `MyBilinearGroupProvider` that implements the interface `BilinearGroupProvider`.
+Then, your group can be registered in the `BilinearGroupFactory` as follows:
+
+```java
+BilinearGroupFactory fac = new BilinearGroupFactory(securityParameter);
+fac.registerProvider(Arrays.asList(new BarretoNaehrigProvider(), new MyBilinearGroupProvider()));
+fac.setRequirements(BilinearGroup.Type.TYPE_3);
+BilinearGroup group = fac.createBilinearGroup();
+```
+
+As an example have a look at our module [upb.crypto.mclwrap](https://github.com/upbcuk/upb.crypto.mclwrap), which includes the pairing library [mcl](https://github.com/herumi/mcl) in our environment.
+
+## Notes
+
+The library was implemented at Paderborn University in the research group ["Codes und Cryptography"](https://cs.uni-paderborn.de/en/cuk/).
+
+This module is the base of [CRACO](https://github.com/upbcuk/upb.crypto.craco) and [CLARC](https://github.com/upbcuk/upb.crypto.clarc) providing cryptographic constructions, and an anonymous credential and reputation system, respectively. 
+
+## Licence
+Apache License 2.0, see LICENCE file.