added comments, reworked a bit, and created warning dialog if some recipients don't have keys saved.

res/values/strings.xml

@@ -61,6 +61,7 @@
     <string name="forward_action">Forward</string>
     <string name="move_action">Move</string>
     <string name="continue_action">Continue</string>
+    <string name="back_action">Back</string>
     <string name="done_action">Done</string> <!--  Used to complete a multi-step process -->
     <string name="remove_action">Remove</string>
     <string name="discard_action">Discard</string>
@@ -1026,6 +1027,9 @@ Welcome to K-9 Mail setup.  K-9 is an open source mail client for Android origin
     <string name="refuse_to_save_draft_marked_encrypted_dlg_title">Refuse to save draft message.</string>
     <string name="refuse_to_save_draft_marked_encrypted_instructions_fmt">Refuse to save draft message marked encrypted.</string>
 
+    <string name="continue_without_public_key_dlg_title">Continue without public key?</string>
+    <string name="continue_without_public_key_instructions_fmt">One or more recipients do not have a saved public key. Continue?</string>
+
     <string name="charset_not_found">This message can\'t be displayed because the charset \"<xliff:g id="charset">%s</xliff:g>\" wasn\'t found.</string>
 
     <string name="select_text_now">Select text to copy.</string>

src/com/fsck/k9/activity/MessageCompose.java

@@ -81,6 +81,7 @@ import com.fsck.k9.mail.store.LocalStore.LocalAttachmentBody;
 public class MessageCompose extends K9Activity implements OnClickListener, OnFocusChangeListener {
     private static final int DIALOG_SAVE_OR_DISCARD_DRAFT_MESSAGE = 1;
     private static final int DIALOG_REFUSE_TO_SAVE_DRAFT_MARKED_ENCRYPTED = 2;
+    private static final int DIALOG_CONTINUE_WITHOUT_PUBLIC_KEY = 3;
 
     private static final String ACTION_COMPOSE = "com.fsck.k9.intent.action.COMPOSE";
     private static final String ACTION_REPLY = "com.fsck.k9.intent.action.REPLY";
@@ -210,6 +211,7 @@ public class MessageCompose extends K9Activity implements OnClickListener, OnFoc
 
     private PgpData mPgpData = null;
     private boolean mAutoEncrypt = false;
+    private boolean mContinueWithoutPublicKey = false;
 
     private String mReferences;
     private String mInReplyTo;
@@ -444,6 +446,8 @@ public class MessageCompose extends K9Activity implements OnClickListener, OnFoc
             public void afterTextChanged(android.text.Editable s) { }
         };
 
+        // For watching changes to the To:, Cc:, and Bcc: fields for auto-encryption on a matching
+        // address.
         TextWatcher recipientWatcher = new TextWatcher() {
             public void beforeTextChanged(CharSequence s, int start, int before, int after) { }
 
@@ -455,10 +459,10 @@ public class MessageCompose extends K9Activity implements OnClickListener, OnFoc
                 final CryptoProvider crypto = mAccount.getCryptoProvider();
                 if (mAutoEncrypt && crypto.isAvailable(getApplicationContext())) {
                     for (Address address : getRecipientAddresses()) {
-                        long ids[] = crypto.getPublicKeyIdsFromEmail(getApplicationContext(),
+                        if (crypto.hasPublicKeyForEmail(getApplicationContext(),
-                                address.getAddress());
+                                address.getAddress())) {
-                        if (ids != null && ids.length > 0) {
                             mEncryptCheckbox.setChecked(true);
+                            mContinueWithoutPublicKey = false;
                             break;
                         }
                     }
@@ -950,6 +954,10 @@ public class MessageCompose extends K9Activity implements OnClickListener, OnFoc
         return Address.parseUnencoded(view.getText().toString().trim());
     }
 
+    /*
+     * Returns an Address array of recipients this email will be sent to.
+     * @return Address array of recipients this email will be sent to.
+     */
     private Address[] getRecipientAddresses() {
         String addresses = mToView.getText().toString() + mCcView.getText().toString()
                 + mBccView.getText().toString();
@@ -1497,20 +1505,20 @@ public class MessageCompose extends K9Activity implements OnClickListener, OnFoc
             Toast.makeText(this, getString(R.string.message_compose_error_no_recipients), Toast.LENGTH_LONG).show();
             return;
         }
+        final CryptoProvider crypto = mAccount.getCryptoProvider();
         if (mEncryptCheckbox.isChecked() && !mPgpData.hasEncryptionKeys()) {
             mMessageFormat = MessageFormat.TEXT;
             // key selection before encryption
             StringBuilder emails = new StringBuilder();
-            Address[][] addresses = new Address[][] { getAddresses(mToView),
+            for (Address address : getRecipientAddresses()) {
-                    getAddresses(mCcView),
-                    getAddresses(mBccView)
-                                                    };
-            for (Address[] addressArray : addresses) {
-                for (Address address : addressArray) {
                 if (emails.length() != 0) {
                     emails.append(',');
                 }
                 emails.append(address.getAddress());
+                if (!mContinueWithoutPublicKey &&
+                        !crypto.hasPublicKeyForEmail(this, address.getAddress())) {
+                    showDialog(DIALOG_CONTINUE_WITHOUT_PUBLIC_KEY);
+                    return;
                 }
             }
             if (emails.length() != 0) {
@@ -1519,7 +1527,7 @@ public class MessageCompose extends K9Activity implements OnClickListener, OnFoc
             emails.append(mIdentity.getEmail());
 
             mPreventDraftSaving = true;
-            if (!mAccount.getCryptoProvider().selectEncryptionKeys(MessageCompose.this, emails.toString(), mPgpData)) {
+            if (!crypto.selectEncryptionKeys(MessageCompose.this, emails.toString(), mPgpData)) {
                 mPreventDraftSaving = false;
             }
             return;
@@ -1528,7 +1536,7 @@ public class MessageCompose extends K9Activity implements OnClickListener, OnFoc
             if (mPgpData.getEncryptedData() == null) {
                 String text = buildText(false).getText();
                 mPreventDraftSaving = true;
-                if (!mAccount.getCryptoProvider().encrypt(this, text, mPgpData)) {
+                if (!crypto.encrypt(this, text, mPgpData)) {
                     mPreventDraftSaving = false;
                 }
                 return;
@@ -2015,6 +2023,24 @@ public class MessageCompose extends K9Activity implements OnClickListener, OnFoc
                 }
             })
                    .create();
+        case DIALOG_CONTINUE_WITHOUT_PUBLIC_KEY:
+            return new AlertDialog.Builder(this)
+                   .setTitle(R.string.continue_without_public_key_dlg_title)
+                   .setMessage(R.string.continue_without_public_key_instructions_fmt)
+            .setPositiveButton(R.string.continue_action, new DialogInterface.OnClickListener() {
+                public void onClick(DialogInterface dialog, int whichButton) {
+                    dismissDialog(DIALOG_CONTINUE_WITHOUT_PUBLIC_KEY);
+                    mContinueWithoutPublicKey = true;
+                    onSend();
+                }
+            })
+            .setNegativeButton(R.string.back_action, new DialogInterface.OnClickListener() {
+                public void onClick(DialogInterface dialog, int whichButton) {
+                    dismissDialog(DIALOG_CONTINUE_WITHOUT_PUBLIC_KEY);
+                    mContinueWithoutPublicKey = false;
+                }
+            })
+                   .create();
         }
         return super.onCreateDialog(id);
     }

src/com/fsck/k9/crypto/Apg.java

@@ -243,11 +243,9 @@ public class Apg extends CryptoProvider {
     public long[] getPublicKeyIdsFromEmail(Context context, String email) {
         long ids[] = null;
         try {
-            Uri contentUri = Uri.withAppendedPath(Apg.CONTENT_URI_PUBLIC_KEY_RING_BY_EMAILS,
+            Uri contentUri = Uri.withAppendedPath(Apg.CONTENT_URI_PUBLIC_KEY_RING_BY_EMAILS, email);
-                                                  email);
             Cursor c = context.getContentResolver().query(contentUri,
-                       new String[] { "master_key_id" },
+                       new String[] { "master_key_id" }, null, null, null);
-                       null, null, null);
             if (c != null && c.getCount() > 0) {
                 ids = new long[c.getCount()];
                 while (c.moveToNext()) {
@@ -267,6 +265,62 @@ public class Apg extends CryptoProvider {
         return ids;
     }
 
+    /**
+     * Find out if a given email has a secret key.
+     *
+     * @param context
+     * @param email The email in question.
+     * @return true if there is a secret key for this email.
+     */
+    @Override
+    public boolean hasSecretKeyForEmail(Context context, String email) {
+        try {
+            Uri contentUri = Uri.withAppendedPath(Apg.CONTENT_URI_SECRET_KEY_RING_BY_EMAILS, email);
+            Cursor c = context.getContentResolver().query(contentUri,
+                    new String[] { "master_key_id" }, null, null, null);
+            if (c != null && c.getCount() > 0) {
+                c.close();
+                return true;
+            }
+            if (c != null) {
+                c.close();
+            }
+        } catch (SecurityException e) {
+            Toast.makeText(context,
+                    context.getResources().getString(R.string.insufficient_apg_permissions),
+                    Toast.LENGTH_LONG).show();
+        }
+        return false;
+    }
+
+    /**
+     * Find out if a given email has a public key.
+     *
+     * @param context
+     * @param email The email in question.
+     * @return true if there is a public key for this email.
+     */
+    @Override
+    public boolean hasPublicKeyForEmail(Context context, String email) {
+        try {
+            Uri contentUri = Uri.withAppendedPath(Apg.CONTENT_URI_PUBLIC_KEY_RING_BY_EMAILS, email);
+            Cursor c = context.getContentResolver().query(contentUri,
+                    new String[] { "master_key_id" }, null, null, null);
+            if (c != null && c.getCount() > 0) {
+                c.close();
+                return true;
+            }
+            if (c != null) {
+                c.close();
+            }
+        } catch (SecurityException e) {
+            Toast.makeText(context,
+                    context.getResources().getString(R.string.insufficient_apg_permissions),
+                    Toast.LENGTH_LONG).show();
+        }
+        return false;
+    }
+
     /**
      * Get the user id based on the key id.
      *

src/com/fsck/k9/crypto/CryptoProvider.java

@@ -25,6 +25,8 @@ abstract public class CryptoProvider {
     abstract public boolean decrypt(Activity activity, String data, PgpData pgpData);
     abstract public long[] getSecretKeyIdsFromEmail(Context context, String email);
     abstract public long[] getPublicKeyIdsFromEmail(Context context, String email);
+    abstract public boolean hasSecretKeyForEmail(Context context, String email);
+    abstract public boolean hasPublicKeyForEmail(Context context, String email);
     abstract public String getUserId(Context context, long keyId);
     abstract public String getName();
     abstract public boolean test(Context context);

src/com/fsck/k9/crypto/None.java

@@ -42,6 +42,16 @@ public class None extends CryptoProvider {
         return null;
     }
 
+    @Override
+    public boolean hasSecretKeyForEmail(Context context, String email) {
+        return false;
+    }
+
+    @Override
+    public boolean hasPublicKeyForEmail(Context context, String email) {
+        return false;
+    }
+
     @Override
     public String getUserId(Context context, long keyId) {
         return null;