Some initial how-do-I

Author: JanBobolz

docs/how-do-I.md

@@ -7,7 +7,29 @@ toc: true
 This page addresses a bunch of questions of the form "how do I do xyz in Cryptimeleon?".
 Consider it Stack-Overflow-style help.
 
-# How do I set up a group?
-# How do I compute a pairing?
-# How do I hash something?
+# How do I do group operations and pairings?
+
+
+# How do I hash into \\(\mathbb{Z}_n\\)?
+You can use `HashIntoZn` for this.
+```java
+BigInteger n = BigInteger.valueOf(99991); //just for the sake of example
+HashIntoZn hashFunction = new HashIntoZn(n);
+Zn.ZnElement hashVal = hashFunction.hash("Preimage");
+```
+
+# How do I hash into a group \\(\mathbb{G}\\)?
+Bilinear groups provide hash functions as follows:
+```java
+GroupElement hashValue = bilinearGroup.getHashIntoG1().hash("Preimage");
+```
+
+For other groups, there may be classes like named like `HashIntoSecp256k1`.
+
+# How do I hash a list of group elements?
+
+
 # How do I send or store a group element?
+
+
+# My benchmark produces implausibly good numbers