ECC documentation

src/site/markdown/usage/certificate.md

@@ -6,7 +6,7 @@ Once you completed all the previous steps, it's time to request the signed certi
 
 To do so, prepare a PKCS#10 CSR file. A single domain may be set as _Common Name_. Multiple domains must be provided as _Subject Alternative Name_. Other properties (_Organization_, _Organization Unit_ etc.) depend on the CA. Some may require these properties to be set, while others may ignore them when generating the certificate.
 
-CSR files can be generated with command line tools like `openssl`. Unfortunately the standard Java does not offer classes for that, so you'd have to resort to [Bouncy Castle](http://www.bouncycastle.org/java.html) if you want to create a CSR programmatically. In the `acme4j-utils` module, there is also a [`CSRBuilder`](../apidocs/org/shredzone/acme4j/util/CSRBuilder.html) for your convenience:
+CSR files can be generated with command line tools like `openssl`. Unfortunately the standard Java does not offer classes for that, so you'd have to resort to [Bouncy Castle](http://www.bouncycastle.org/java.html) if you want to create a CSR programmatically. In the `acme4j-utils` module, there is also a [`CSRBuilder`](../apidocs/org/shredzone/acme4j/util/CSRBuilder.html) for your convenience. You can also use [`KeyPairUtils`](../apidocs/org/shredzone/acme4j/util/KeyPairUtils.html) for generating the domain key pair.
 
 ```java
 KeyPair domainKeyPair = ... // KeyPair to be used for HTTPS encryption

src/site/markdown/usage/register.md

@@ -60,3 +60,35 @@ client.changeRegistrationKey(reg, newKeyPair);
 ```
 
 All subsequent calls must now use the new key pair. The old key pair can be disposed.
+
+## Key Pair Utilities
+
+The `KeyPairUtils` class in the `acme4j-utils` module provides a few methods to make key pair handling more convenient.
+
+This call will generate a RSA key pair with a 2048 bit key:
+
+```java
+KeyPair keyPair = KeyPairUtils.createKeyPair(2048);
+```
+
+You can also create an elliptic curve key pair:
+
+```java
+KeyPair keyPair = KeyPairUtils.createECKeyPair("secp256r1");
+```
+
+To save a `KeyPair` (actually, the private key of the key pair) to a pem file, use this snippet:
+
+```java
+try (FileWriter fw = new FileWriter("keypair.pem")) {
+  KeyPairUtils.writeKeyPair(keyPair, fw);
+}
+```
+
+The following snippet reads the private key from a pem file, and returns a `KeyPair`.
+
+```java
+try (FileReader fr = New FileReader("keypair.pem")) {
+  return KeyPairUtils.readKeyPair(fr);
+}
+```