[Tinyos-devel] Re: PATCH for TinySec

[Irfan Acar]

> --- CBCMAC.nc   7 Oct 2003 21:46:22 -0000       1.2
> +++ CBCMAC.nc   7 Jul 2006 17:41:52 -0000
> @@ -155,7 +155,7 @@
>         for (i = 0; i < msgLen; i++) {
>           // unroll
>           partial[pos++] ^= msg[i];
> -        if (pos == 7) {
> +        if (pos == 8) {
>             if (!call BlockCipher.encrypt (&context->cc, partial, partial)) {
>               return FAIL;
>             }
> 

The patch below fixes the bug mentioned and a couple other problems.

1) Hard-coded values are expressed in terms of CBCMAC_BLOCK_SIZE.

2) Incorrect uint8_t declarations replaced with uint16_t.


--- CBCMAC.nc
+++ CBCMAC.nc
@@ -114,11 +114,11 @@
        // temp buffer to hold length buffer which we'll encrypt to the
        // real "partial" stored in the context.
        uint8_t partial[CBCMAC_BLOCK_SIZE];
-      // length divided by 8 [ ie num blocks]
-      uint8_t numBlocks = length >> 3;
-      memset (partial, 0, 6);
-      partial[6] = (numBlocks >> 8) & 0xff;
-      partial[7] = (numBlocks & 0xff);
+      // length divided by CBCMAC_BLOCK_SIZE [ ie num blocks]
+      uint16_t numBlocks = length / CBCMAC_BLOCK_SIZE;
+      memset (partial, 0, CBCMAC_BLOCK_SIZE-2);
+      partial[CBCMAC_BLOCK_SIZE-2] = (numBlocks >> 8) & 0xff;
+      partial[CBCMAC_BLOCK_SIZE-1] = (numBlocks & 0xff);

        ((CBCMACContext*) context->context)->length = length;
        ((CBCMACContext*) context->context)->blockPos = 0;
@@ -143,7 +143,8 @@
    async command result_t MAC.incrementalMAC (MACContext * context, uint8_t * msg,
                                              uint16_t msgLen)
      {
-      uint8_t i, pos = ((CBCMACContext*) context->context)->blockPos;
+      uint16_t i;
+      uint8_t pos = ((CBCMACContext*) context->context)->blockPos;
        uint8_t * partial = ((CBCMACContext*) context->context)->partial;

        // only proceed if the we're expecting less than msgLen of data.
@@ -155,7 +156,7 @@
        for (i = 0; i < msgLen; i++) {
          // unroll
          partial[pos++] ^= msg[i];
-        if (pos == 7) {
+        if (pos == CBCMAC_BLOCK_SIZE) {
            if (!call BlockCipher.encrypt (&context->cc, partial, partial)) {
              return FAIL;
            }
@@ -192,7 +193,7 @@
        uint8_t * partial = ((CBCMACContext*) context->context)->partial;
        // make sure they're asking for a valid mac size and that we've received
        // all the data that we're expecting.
-      if (! macSize || macSize > 8 ||
+      if (! macSize || macSize > CBCMAC_BLOCK_SIZE ||
            ((CBCMACContext*) context->context)->length) {
         dbg(DBG_CRYPTO,"MAC getIncrementalMAC failure: length left %d.\n",
             ((CBCMACContext*) context->context)->length);