diff --git a/pgp-certificate-store/src/main/java/pgp/certificate_store/SubkeyLookup.java b/pgp-certificate-store/src/main/java/pgp/certificate_store/SubkeyLookup.java
index 73e396b..34081b0 100644
--- a/pgp-certificate-store/src/main/java/pgp/certificate_store/SubkeyLookup.java
+++ b/pgp-certificate-store/src/main/java/pgp/certificate_store/SubkeyLookup.java
@@ -8,6 +8,12 @@ import java.io.IOException;
 import java.util.List;
 import java.util.Set;
 
+/**
+ * The {@link SubkeyLookup} class defines an interface for recording and looking up, to which certificates
+ * a certain subkey belongs to.
+ *
+ * For a basic implementation it is enough to implement CR (out of CRUD) operations.
+ */
 public interface SubkeyLookup {
 
     /**
diff --git a/pgp-certificates/src/main/java/pgp/Certificate.java b/pgp-certificates/src/main/java/pgp/Certificate.java
index d481e6a..913a070 100644
--- a/pgp-certificates/src/main/java/pgp/Certificate.java
+++ b/pgp-certificates/src/main/java/pgp/Certificate.java
@@ -10,8 +10,8 @@ import java.util.Set;
 
 public abstract class Certificate {
     /**
-     * Return the fingerprint of the certificate as 40 lowercase hex characters.
-     * TODO: Allow OpenPGP V5 fingerprints
+     * Return the fingerprint of the certificate as lowercase hex characters.
+     * OpenPGP v4 fingerprints consist of 40 characters, while OpenPGP v5 fingerprints consist of 64.
      *
      * @return fingerprint
      */