--- a/common-algo.c	Wed May 09 22:52:58 2012 +0800
+++ b/common-algo.c	Thu May 17 00:12:42 2012 +0800
@@ -260,8 +260,6 @@
 	return DROPBEAR_FAILURE;
 }
 
-
-
 /* Output a comma separated list of algorithms to a buffer */
 void buf_put_algolist(buffer * buf, algo_type localalgos[]) {
 
@@ -282,3 +280,99 @@
 	buf_putstring(buf, algolist->data, algolist->len);
 	buf_free(algolist);
 }
+
+#ifdef ENABLE_USER_ALGO_LIST
+
+char *
+algolist_string(algo_type algos[])
+{
+	char *ret_list;
+	buffer *b = buf_new(200);
+	buf_put_algolist(b, algos);
+	buf_setpos(b, b->len);
+	buf_putbyte(b, '\0');
+	buf_setpos(b, 4);
+	ret_list = m_strdup(buf_getptr(b, b->len - b->pos));
+	buf_free(b);
+	return ret_list;
+}
+
+static int
+check_algo(const char* algo_name, algo_type *algos)
+{
+	algo_type *a;
+	for (a = algos; a->name != NULL; a++)
+	{
+		if (strcmp(a->name, algo_name) == 0)
+		{
+			a->usable = 2;
+			return DROPBEAR_SUCCESS;
+		}
+	}
+
+	return DROPBEAR_FAILURE;
+}
+
+/* helper for check_user_algos */
+static void
+try_add_algo(const char *algo_name, algo_type *algos, 
+		const char *algo_desc, char ** out_list, int *num_ret)
+{
+	if (check_algo(algo_name, algos) == DROPBEAR_FAILURE)
+	{
+		dropbear_log(LOG_WARNING, "This Dropbear program does not support '%s' %s algorithm", algo_name, algo_desc);
+		return;
+	}
+
+	if (*num_ret != 0)
+	{
+		**out_list = ',';
+		(*out_list)++;
+	}
+
+	*out_list += sprintf(*out_list, "%s", algo_name);
+	(*num_ret)++;
+}
+
+/* Checks a user provided comma-separated algorithm list for available
+ * options. Any that are not acceptable are removed in-place. Returns the
+ * number of valid algorithms. */
+int
+check_user_algos(char* user_algo_list, algo_type * algos, 
+		const char *algo_desc)
+{
+	/* this has two passes. first we sweep through the given list of
+	 * algorithms and mark them as usable=2 in the algo_type[] array... */
+	int num_ret = 0;
+	char *work_list = m_strdup(user_algo_list);
+	char *last_name = work_list;
+	char *out_list = user_algo_list;
+	char *c;
+	for (c = work_list; *c; c++)
+	{
+		if (*c == ',')
+		{
+			*c = '\0';
+			try_add_algo(last_name, algos, algo_desc, &out_list, &num_ret);
+			last_name = c++;
+		}
+	}
+	try_add_algo(last_name, algos, algo_desc, &out_list, &num_ret);
+	m_free(work_list);
+
+	/* ...then we mark anything with usable==1 as usable=0, and 
+	 * usable==2 as usable=1. */
+	algo_type *a;
+	for (a = algos; a->name != NULL; a++)
+	{
+		if (a->usable == 1)
+		{
+			a->usable = 0;
+		} else if (a->usable == 2)
+		{
+			a->usable = 1;
+		}
+	}
+	return num_ret;
+}
+#endif // ENABLE_USER_ALGO_LIST