Update readme

README.md

@@ -1,6 +1,6 @@
 # Single Step KDF (NIST SP 800-56A)
 
-WIP
+This is an implementation of the single-step key derivation function as described in [NIST SP 800-56A revision 1, chapter 4](https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-56Cr1.pdf). It is an unopinionated approach towards the subject, allowing all 3 options (message digest, hmac and kmac) as H function and leaving open the exact format of the `fixedInfo` parameter.
 
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@@ -22,17 +22,27 @@ Add dependency to your `pom.xml`:
 A very simple example:
 
 ```java
-TBD
+// a shared secret provided by your protocol
+byte[] sharedSecret = ...
+// a salt; if you don't have access to a salt use SingleStepKdf.fromSha256() or similar
+byte[] salt = ...
+// other info to bind the key to the context, see the NIST spec for more detail
+byte[] otherInfo = "macKey".getBytes();
+byte[] keyMaterial = SingleStepKdf.fromHmacSha256().derive(sharedSecret, 32, salt, otherInfo);
+SecretKey secretKey = new SecretKeySpec(keyMaterial, "AES");
 ```
 
 ### Full Example
 
+### Using with Message Digest (Option 1)
 
 ```java
 TBD
 ```
+### Using with HMAC (Option 2)
+
 
-### Using custom HMAC implementation
+### Using custom Message Digest / HMAC implementation
 
 ```java
 TBD

src/test/java/at/favre/lib/crypto/SingleStepKdfTest.java

@@ -3,10 +3,27 @@
 import at.favre.lib.bytes.Bytes;
 import org.junit.Test;
 
+import javax.crypto.SecretKey;
+import javax.crypto.spec.SecretKeySpec;
+
+import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.fail;
 
 public class SingleStepKdfTest {
 
+    @Test
+    public void quickstart() {
+        // a shared secret provided by your protocol
+        byte[] sharedSecret = Bytes.random(16).array();
+        // a salt; if you don't have access to a salt use SingleStepKdf.fromSha256() or similar
+        byte[] salt = Bytes.random(16).array();
+        // other info to bind the key to the context, see the NIST spec for more detail
+        byte[] otherInfo = "macKey".getBytes();
+        byte[] keyMaterial = SingleStepKdf.fromHmacSha256().derive(sharedSecret, 32, salt, otherInfo);
+        SecretKey secretKey = new SecretKeySpec(keyMaterial, "AES");
+        assertNotNull(secretKey);
+    }
+
     @Test
     public void testIllegalOutLength() {
         SingleStepKdf kdf = SingleStepKdf.fromSha256();