diff --git a/library/ccm.c b/library/ccm.c
index 399b9fe..fafa238 100644
--- a/library/ccm.c
+++ b/library/ccm.c
@@ -146,9 +146,6 @@
     if( add_len > 0xFF00 )
         return( POLARSSL_ERR_CCM_BAD_INPUT );
 
-    if( mode != CCM_ENCRYPT )
-        return( POLARSSL_ERR_CCM_BAD_INPUT ); /* Not implemented yet */
-
     /*
      * First block B_0:
      * 0        .. 0        flags
@@ -238,18 +235,34 @@
     dst = output;
 
     /*
-     * Authenticate and encrypt message
+     * Authenticate and crypt message
+     * The only difference between encryption and decryption is
+     * the respective order of authentication and {en,de}cryption
      */
     while( len_left > 16 )
     {
-        memcpy( b, src, 16 );
-        UPDATE_CBC_MAC( b );
+        if( mode == CCM_ENCRYPT )
+        {
+            memcpy( b, src, 16 );
+            UPDATE_CBC_MAC( b );
+        }
+
         CTR_CRYPT_BLOCK( dst, src );
 
+        if( mode == CCM_DECRYPT )
+        {
+            memcpy( b, dst, 16 );
+            UPDATE_CBC_MAC( b );
+        }
+
         dst += 16;
         src += 16;
         len_left -= 16;
 
+        /*
+         * Increment counter.
+         * No need to check for overflow thanks to the length check above.
+         */
         for( i = 0; i < q; i++ )
             if( ++ctr[15-i] != 0 )
                 break;
@@ -260,10 +273,12 @@
         unsigned char mask[16];
         size_t olen;
 
-        memset( b, 0, 16 );
-        memcpy( b, src, len_left );
-
-        UPDATE_CBC_MAC( b );
+        if( mode == CCM_ENCRYPT )
+        {
+            memset( b, 0, 16 );
+            memcpy( b, src, len_left );
+            UPDATE_CBC_MAC( b );
+        }
 
         if( ( ret = cipher_update( &ctx->cipher_ctx, ctr, 16,
                                    mask, &olen ) ) != 0 )
@@ -273,10 +288,17 @@
 
         for( i = 0; i < len_left; i++ )
             dst[i] = src[i] ^ mask[i];
+
+        if( mode == CCM_DECRYPT )
+        {
+            memset( b, 0, 16 );
+            memcpy( b, dst, len_left );
+            UPDATE_CBC_MAC( b );
+        }
     }
 
     /*
-     * Authentication: reset counter and encrypt internal tag
+     * Authentication: reset counter and {en,de}crypt internal tag
      */
     for( i = 0; i < q; i++ )
         ctr[15-i] = 0;
@@ -410,10 +432,10 @@
         if( verbose != 0 )
             polarssl_printf( "  CCM-AES #%u: ", (unsigned int) i + 1 );
 
-        ret =  ccm_encrypt_and_tag( &ctx, msg_len[i],
-                                    iv, iv_len[i], ad, add_len[i],
-                                    msg, out,
-                                    out + msg_len[i], tag_len[i] );
+        ret = ccm_encrypt_and_tag( &ctx, msg_len[i],
+                                   iv, iv_len[i], ad, add_len[i],
+                                   msg, out,
+                                   out + msg_len[i], tag_len[i] );
 
         if( ret != 0 ||
             memcmp( out, res[i], msg_len[i] + tag_len[i] ) != 0 )
@@ -424,6 +446,20 @@
             return( 1 );
         }
 
+        ret = ccm_auth_decrypt( &ctx, msg_len[i],
+                                iv, iv_len[i], ad, add_len[i],
+                                res[i], out,
+                                res[i] + msg_len[i], tag_len[i] );
+
+        if( ret != 0 ||
+            memcmp( out, msg, msg_len[i] ) != 0 )
+        {
+            if( verbose != 0 )
+                polarssl_printf( "failed\n" );
+
+            return( 1 );
+        }
+
         if( verbose != 0 )
             polarssl_printf( "passed\n" );
     }