make the mppe salt unique

diff --git a/src/libcharon/plugins/tnc_pdp/tnc_pdp.c b/src/libcharon/plugins/tnc_pdp/tnc_pdp.c
index 3aa2c88..f32d541 100644 (file)
--- a/src/libcharon/plugins/tnc_pdp/tnc_pdp.c
+++ b/src/libcharon/plugins/tnc_pdp/tnc_pdp.c
@@ -187,7 +187,8 @@ static void send_message(private_tnc_pdp_t *this, radius_message_t *message,
  * Encrypt a MS-MPPE-Send/Recv-Key
  */
 static chunk_t encrypt_mppe_key(private_tnc_pdp_t *this, u_int8_t type,
-                                                               chunk_t key, radius_message_t *request)
+                                                               chunk_t key, u_int16_t *salt,
+                                                               radius_message_t *request)
 {
        chunk_t a, r, seed, data;
        u_char b[HASH_SIZE_MD5], *c;
@@ -213,17 +214,25 @@ static chunk_t encrypt_mppe_key(private_tnc_pdp_t *this, u_int8_t type,
 
        memcpy(&mppe_key->key[1], key.ptr, key.len);
 
-       /* generate a 16 bit random salt value */
+       /**
+        * generate a 16 bit unique random salt value for the MPPE stream cipher
+        * the MSB of the salt MUST be set to 1
+        */
        a = chunk_create((u_char*)&(mppe_key->salt), sizeof(mppe_key->salt));
-       this->rng->get_bytes(this->rng, a.len, a.ptr);
+       do
+       {
+               this->rng->get_bytes(this->rng, a.len, a.ptr);
+               *a.ptr |= 0x80;
+       }
+       while (mppe_key->salt == *salt);
 
-       /* the MSB of the salt MUST be set to 1 */
-       *a.ptr |= 0x80;
+       /* update the salt value */
+       *salt = mppe_key->salt;
 
        r = chunk_create(request->get_authenticator(request), HASH_SIZE_MD5);
        seed = chunk_cata("cc", r, a);
-       c = mppe_key->key;
 
+       c = mppe_key->key;
        while (c < data.ptr + data.len)
        {
                /* b(i) = MD5(S + c(i-1)) */
@@ -251,6 +260,7 @@ static void send_response(private_tnc_pdp_t *this, radius_message_t *request,
        radius_message_t *response;
        chunk_t data, recv, send;
        u_int32_t tunnel_type;
+       u_int16_t salt = 0;
 
        response = radius_message_create(code);
        if (eap)
@@ -278,12 +288,12 @@ static void send_response(private_tnc_pdp_t *this, radius_message_t *request,
        if (msk.len)
        {
                recv = chunk_create(msk.ptr, msk.len / 2);
-               data = encrypt_mppe_key(this, MS_MPPE_RECV_KEY, recv, request);
+               data = encrypt_mppe_key(this, MS_MPPE_RECV_KEY, recv, &salt, request);
                response->add(response, RAT_VENDOR_SPECIFIC, data);
                chunk_free(&data);
                
                send = chunk_create(msk.ptr + recv.len, msk.len - recv.len);
-               data = encrypt_mppe_key(this, MS_MPPE_SEND_KEY, send, request);
+               data = encrypt_mppe_key(this, MS_MPPE_SEND_KEY, send, &salt, request);
                response->add(response, RAT_VENDOR_SPECIFIC, data);
                chunk_free(&data);
        }