Fix check for short rsa keys.

And add a comment that explains the magic constant 41.

diff --git a/user_list.c b/user_list.c
index 3c0b4f856546a2173c77696f80e0c554a646985c..f1b4b212e11f3e1d807d9a78d1ac31b6d17cf9ca 100644 (file)
--- a/user_list.c
+++ b/user_list.c
@@ -18,6 +18,7 @@
 #include "string.h"
 #include "list.h"
 #include "user_list.h"
+#include "rc4.h"
 
 static struct list_head user_list;
 
@@ -56,8 +57,15 @@ static void populate_user_list(char *user_list_file)
                                para_strerror(-ret));
                        continue;
                }
-               if (ret < CHALLENGE_SIZE + 2 * CHALLENGE_SIZE + 41) {
-                       PARA_WARNING_LOG("rsa key for %s too small\n", n);
+               /*
+                * In order to encrypt len := CHALLENGE_SIZE + 2 * RC4_KEY_LEN
+                * bytes using RSA_public_encrypt() with EME-OAEP padding mode,
+                * RSA_size(rsa) must be greater than len + 41. So ignore keys
+                * which are too short. For details see RSA_public_encrypt(3).
+                */
+               if (ret <= CHALLENGE_SIZE + 2 * RC4_KEY_LEN + 41) {
+                       PARA_WARNING_LOG("rsa key %s too short (%d)\n",
+                               k, ret);
                        rsa_free(rsa);
                        continue;
                }