diff -r 773899cbd05a -r 5749f2724b12 libpurple/cipher.c
--- a/libpurple/cipher.c	Sun May 05 14:59:11 2013 +0200
+++ b/libpurple/cipher.c	Sun May 05 15:37:25 2013 +0200
@@ -108,6 +108,8 @@
 		caps |= PURPLE_CIPHER_CAPS_GET_SALT_SIZE;
 	if(ops->set_key)
 		caps |= PURPLE_CIPHER_CAPS_SET_KEY;
+	if (ops->get_key_size)
+		caps |= PURPLE_CIPHER_CAPS_GET_KEY_SIZE;
 	if(ops->set_batch_mode)
 		caps |= PURPLE_CIPHER_CAPS_SET_BATCH_MODE;
 	if(ops->get_batch_mode)
@@ -570,6 +572,25 @@
 						"set_key operation\n", cipher->name);
 }
 
+size_t
+purple_cipher_context_get_key_size(PurpleCipherContext *context) {
+	PurpleCipher *cipher = NULL;
+
+	g_return_val_if_fail(context, 0);
+
+	cipher = context->cipher;
+	g_return_val_if_fail(cipher, 0);
+
+	if (cipher->ops && cipher->ops->get_key_size)
+		return cipher->ops->get_key_size(context);
+	else {
+		purple_debug_warning("cipher", "the %s cipher does not support "
+			"the get_key_size operation\n", cipher->name);
+
+		return 0;
+	}
+}
+
 void
 purple_cipher_context_set_batch_mode(PurpleCipherContext *context,
                                      PurpleCipherBatchMode mode)