add some comments to previous commit

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/pgp/PgpSignEncrypt.java

@@ -335,6 +335,7 @@ public class PgpSignEncrypt {
                 throw new NoSigningKeyException();
             }
 
+            // Make sure we are allowed to sign here!
             if ( ! signingKey.canSign()) {
                 throw new NoSigningKeyException();
             }

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/service/KeychainIntentService.java

@@ -281,11 +281,17 @@ public class KeychainIntentService extends IntentService implements Progressable
                             .setOriginalFilename(originalFilename);
 
                     try {
+
+                        // Find the appropriate subkey to sign with
                         CachedPublicKeyRing signingRing =
                                 new ProviderHelper(this).getCachedPublicKeyRing(sigMasterKeyId);
                         long sigSubKeyId = signingRing.getSignId();
-                        // It is assumed that the passphrase was cached prior to the service call.
+
+                        // Get its passphrase from cache. It is assumed that this passphrase was
+                        // cached prior to the service call.
                         String passphrase = PassphraseCacheService.getCachedPassphrase(this, sigSubKeyId);
+
+                        // Set signature settings
                         builder.setSignatureMasterKeyId(sigMasterKeyId)
                                 .setSignatureSubKeyId(sigSubKeyId)
                                 .setSignaturePassphrase(passphrase)

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/ui/EncryptTextActivity.java

@@ -72,6 +72,7 @@ public class EncryptTextActivity extends DrawerActivity implements EncryptActivi
     // model used by fragments
     private long mEncryptionKeyIds[] = null;
     private String mEncryptionUserIds[] = null;
+    // TODO Constants.key.none? What's wrong with a null value?
     private long mSigningKeyId = Constants.key.none;
     private String mPassphrase = "";
     private boolean mShareAfterEncrypt = false;
@@ -313,10 +314,13 @@ public class EncryptTextActivity extends DrawerActivity implements EncryptActivi
             }
 
             try {
+                // TODO This should really not be decided here. We do need the info for the passphrase
+                // TODO dialog fragment though, so that's just the way it is for now.
                 if (mSigningKeyId != 0) {
                     CachedPublicKeyRing signingRing =
                             new ProviderHelper(this).getCachedPublicKeyRing(mSigningKeyId);
                     long sigSubKeyId = signingRing.getSignId();
+                    // Make sure the passphrase is cached, then start over.
                     if (PassphraseCacheService.getCachedPassphrase(this, sigSubKeyId) == null) {
                         PassphraseDialogFragment.show(this, sigSubKeyId,
                                 new Handler() {