Changeset ddcf491f for lib

Timestamp:

2008-03-16T14:18:22Z (16 years ago)

Author:

Wilmer van der Gaast <wilmer@…>

Branches:

master

Children:

e960a52

Parents:

d07c3a8

Message:

Adding padding to encrypted IM-passwords so the exact password length can't
be guessed from the encrypted data anymore.

Location:

lib

Files:

• arc.c (modified) (2 diffs)
• arc.h (modified) (1 diff)

lib/arc.c

@@ -131 +131 @@
    
    Both functions return the number of bytes in the result string.
+   
+   Note that if you use the pad_to argument, you will need zero-termi-
+   nation to find back the original string length after decryption. So
+   it shouldn't be used if your string contains \0s by itself!
 */
 
-int arc_encode( char *clear, int clear_len, unsigned char **crypt, char *password )
+int arc_encode( char *clear, int clear_len, unsigned char **crypt, char *password, int pad_to )
 {
         struct arc_state *st;
         unsigned char *key;
-        int key_len, i;
+        char *padded = NULL;
+        int key_len, i, padded_len;
         
         key_len = strlen( password ) + ARC_IV_LEN;
         if( clear_len <= 0 )
                 clear_len = strlen( clear );
+        
+        /* Pad the string to the closest multiple of pad_to. This makes it
+           impossible to see the exact length of the password. */
+        if( pad_to > 0 && ( clear_len % pad_to ) > 0 )
+        {
+                padded_len = clear_len + pad_to - ( clear_len % pad_to );
+                padded = g_malloc( padded_len );
+                memcpy( padded, clear, clear_len );
+                
+                /* First a \0 and then random data, so we don't have to do
+                   anything special when decrypting. */
+                padded[clear_len] = 0;
+                random_bytes( (unsigned char*) padded + clear_len + 1, padded_len - clear_len - 1 );
+                
+                clear = padded;
+                clear_len = padded_len;
+        }
         
         /* Prepare buffers and the key + IV */
@@ -161 +183 @@
         
         g_free( st );
+        g_free( padded );
         
         return clear_len + ARC_IV_LEN;

lib/arc.h

@@ -31 +31 @@
 };
 
-struct arc_state *arc_keymaker( unsigned char *key, int kl, int cycles );
+G_GNUC_MALLOC struct arc_state *arc_keymaker( unsigned char *key, int kl, int cycles );
 unsigned char arc_getbyte( struct arc_state *st );
-int arc_encode( char *clear, int clear_len, unsigned char **crypt, char *password );
+int arc_encode( char *clear, int clear_len, unsigned char **crypt, char *password, int pad_to );
 int arc_decode( unsigned char *crypt, int crypt_len, char **clear, char *password );