Add some missing javadoc

build.gradle

@@ -258,6 +258,18 @@ task javadocAll(type: Javadoc) {
     ] as String[]
 }
 
+if (JavaVersion.current().isJava8Compatible()) {
+    tasks.withType(Javadoc) {
+        // The '-quiet' as second argument is actually a hack,
+        // since the one paramater addStringOption doesn't seem to
+        // work, we extra add '-quiet', which is added anyway by
+        // gradle. See https://github.com/gradle/gradle/issues/2354
+        // See JDK-8200363 (https://bugs.openjdk.java.net/browse/JDK-8200363)
+        // for information about the -Xwerror option.
+        options.addStringOption('Xwerror', '-quiet')
+    }
+}
+
 /**
  * Fetch sha256 checksums of artifacts published to maven central.
  *

pgpainless-cli/src/main/java/org/pgpainless/cli/PGPainlessCLI.java

@@ -18,6 +18,10 @@ public class PGPainlessCLI {
         SopCLI.setSopInstance(new SOPImpl());
     }
 
+    /**
+     * Main method of the CLI application.
+     * @param args arguments
+     */
     public static void main(String[] args) {
         int result = execute(args);
         if (result != 0) {
@@ -25,6 +29,12 @@ public class PGPainlessCLI {
         }
     }
 
+    /**
+     * Execute the given command and return the exit code of the program.
+     *
+     * @param args command string array (e.g. ["pgpainless-cli", "generate-key", "Alice"])
+     * @return exit code
+     */
     public static int execute(String... args) {
         return SopCLI.execute(args);
     }

pgpainless-sop/src/main/java/org/pgpainless/sop/ArmorImpl.java

@@ -18,6 +18,9 @@ import sop.enums.ArmorLabel;
 import sop.exception.SOPGPException;
 import sop.operation.Armor;
 
+/**
+ * Implementation of the <pre>armor</pre> operation using PGPainless.
+ */
 public class ArmorImpl implements Armor {
 
     @Override

pgpainless-sop/src/main/java/org/pgpainless/sop/DearmorImpl.java

@@ -15,6 +15,9 @@ import sop.Ready;
 import sop.exception.SOPGPException;
 import sop.operation.Dearmor;
 
+/**
+ * Implementation of the <pre>dearmor</pre> operation using PGPainless.
+ */
 public class DearmorImpl implements Dearmor {
 
     @Override

pgpainless-sop/src/main/java/org/pgpainless/sop/DecryptImpl.java

@@ -34,6 +34,9 @@ import sop.Verification;
 import sop.exception.SOPGPException;
 import sop.operation.Decrypt;
 
+/**
+ * Implementation of the <pre>decrypt</pre> operation using PGPainless.
+ */
 public class DecryptImpl implements Decrypt {
 
     private final ConsumerOptions consumerOptions = ConsumerOptions.get();

pgpainless-sop/src/main/java/org/pgpainless/sop/DetachedSignImpl.java

@@ -36,6 +36,9 @@ import sop.enums.SignAs;
 import sop.exception.SOPGPException;
 import sop.operation.DetachedSign;
 
+/**
+ * Implementation of the <pre>sign</pre> operation using PGPainless.
+ */
 public class DetachedSignImpl implements DetachedSign {
 
     private boolean armor = true;

pgpainless-sop/src/main/java/org/pgpainless/sop/DetachedVerifyImpl.java

@@ -23,6 +23,9 @@ import sop.Verification;
 import sop.exception.SOPGPException;
 import sop.operation.DetachedVerify;
 
+/**
+ * Implementation of the <pre>verify</pre> operation using PGPainless.
+ */
 public class DetachedVerifyImpl implements DetachedVerify {
 
     private final ConsumerOptions options = ConsumerOptions.get();

pgpainless-sop/src/main/java/org/pgpainless/sop/EncryptImpl.java

@@ -34,6 +34,9 @@ import sop.exception.SOPGPException;
 import sop.operation.Encrypt;
 import sop.util.ProxyOutputStream;
 
+/**
+ * Implementation of the <pre>encrypt</pre> operation using PGPainless.
+ */
 public class EncryptImpl implements Encrypt {
 
     EncryptionOptions encryptionOptions = EncryptionOptions.get();

pgpainless-sop/src/main/java/org/pgpainless/sop/ExtractCertImpl.java

@@ -19,6 +19,9 @@ import sop.Ready;
 import sop.exception.SOPGPException;
 import sop.operation.ExtractCert;
 
+/**
+ * Implementation of the <pre>extract-cert</pre> operation using PGPainless.
+ */
 public class ExtractCertImpl implements ExtractCert {
 
     private boolean armor = true;

pgpainless-sop/src/main/java/org/pgpainless/sop/GenerateKeyImpl.java

@@ -24,6 +24,9 @@ import sop.Ready;
 import sop.exception.SOPGPException;
 import sop.operation.GenerateKey;
 
+/**
+ * Implementation of the <pre>generate-key</pre> operation using PGPainless.
+ */
 public class GenerateKeyImpl implements GenerateKey {
 
     private boolean armor = true;

pgpainless-sop/src/main/java/org/pgpainless/sop/InlineDetachImpl.java

@@ -30,6 +30,9 @@ import sop.Signatures;
 import sop.exception.SOPGPException;
 import sop.operation.InlineDetach;
 
+/**
+ * Implementation of the <pre>inline-detach</pre> operation using PGPainless.
+ */
 public class InlineDetachImpl implements InlineDetach {
 
     private boolean armor = true;

pgpainless-sop/src/main/java/org/pgpainless/sop/InlineSignImpl.java

@@ -29,6 +29,9 @@ import sop.enums.InlineSignAs;
 import sop.exception.SOPGPException;
 import sop.operation.InlineSign;
 
+/**
+ * Implementation of the <pre>inline-sign</pre> operation using PGPainless.
+ */
 public class InlineSignImpl implements InlineSign {
 
     private boolean armor = true;

pgpainless-sop/src/main/java/org/pgpainless/sop/InlineVerifyImpl.java

@@ -26,6 +26,9 @@ import sop.Verification;
 import sop.exception.SOPGPException;
 import sop.operation.InlineVerify;
 
+/**
+ * Implementation of the <pre>inline-verify</pre> operation using PGPainless.
+ */
 public class InlineVerifyImpl implements InlineVerify {
 
     private final ConsumerOptions options = ConsumerOptions.get();

pgpainless-sop/src/main/java/org/pgpainless/sop/KeyReader.java

@@ -13,6 +13,9 @@ import sop.exception.SOPGPException;
 import java.io.IOException;
 import java.io.InputStream;
 
+/**
+ * Reader for OpenPGP keys and certificates with error matching according to the SOP spec.
+ */
 class KeyReader {
 
     static PGPSecretKeyRingCollection readSecretKeys(InputStream keyInputStream, boolean requireContent)

pgpainless-sop/src/main/java/org/pgpainless/sop/MatchMakingSecretKeyRingProtector.java

@@ -20,12 +20,21 @@ import org.pgpainless.key.protection.SecretKeyRingProtector;
 import org.pgpainless.key.protection.UnlockSecretKey;
 import org.pgpainless.util.Passphrase;
 
+/**
+ * Implementation of the {@link SecretKeyRingProtector} which can be handed passphrases and keys separately,
+ * and which then matches up passphrases and keys when needed.
+ */
 public class MatchMakingSecretKeyRingProtector implements SecretKeyRingProtector {
 
     private final Set<Passphrase> passphrases = new HashSet<>();
     private final Set<PGPSecretKeyRing> keys = new HashSet<>();
     private final CachingSecretKeyRingProtector protector = new CachingSecretKeyRingProtector();
 
+    /**
+     * Add a single passphrase to the protector.
+     *
+     * @param passphrase passphrase
+     */
     public void addPassphrase(Passphrase passphrase) {
         if (passphrase.isEmpty()) {
             return;
@@ -46,6 +55,11 @@ public class MatchMakingSecretKeyRingProtector implements SecretKeyRingProtector
         }
     }
 
+    /**
+     * Add a single {@link PGPSecretKeyRing} to the protector.
+     *
+     * @param key secret keys
+     */
     public void addSecretKey(PGPSecretKeyRing key) {
         if (!keys.add(key)) {
             return;
@@ -89,6 +103,9 @@ public class MatchMakingSecretKeyRingProtector implements SecretKeyRingProtector
         return protector.getEncryptor(keyId);
     }
 
+    /**
+     * Clear all known passphrases from the protector.
+     */
     public void clear() {
         for (Passphrase passphrase : passphrases) {
             passphrase.clear();

pgpainless-sop/src/main/java/org/pgpainless/sop/SOPImpl.java

@@ -19,6 +19,12 @@ import sop.operation.InlineSign;
 import sop.operation.InlineVerify;
 import sop.operation.Version;
 
+/**
+ * Implementation of the <pre>sop</pre> API using PGPainless.
+ * <pre> {@code
+ * SOP sop = new SOPImpl();
+ * }</pre>
+ */
 public class SOPImpl implements SOP {
 
     static {

pgpainless-sop/src/main/java/org/pgpainless/sop/VersionImpl.java

@@ -12,6 +12,9 @@ import java.util.Properties;
 import org.bouncycastle.jce.provider.BouncyCastleProvider;
 import sop.operation.Version;
 
+/**
+ * Implementation of the <pre>version</pre> operation using PGPainless.
+ */
 public class VersionImpl implements Version {
 
     // draft version