[MOD] HMAC-based mediachecking

src/MatrixEventHandler.c

@@ -25,8 +25,8 @@ JoinMUC(ParseeData *data, HashMap *event, char *jid, char *muc, char *name)
     while (!XMPPJoinMUC(data->jabber, jid, rev, true) && nonce < 32)
     {
         char *nonce_str = StrInt(nonce);
-        char *input = StrConcat(4, sender, name, data->id, nonce_str);
-        char *hex = ParseeSHA256(input);
+        char *input = StrConcat(3, sender, name, nonce_str);
+        char *hex = ParseeHMACS(data->id, input);
 
         if (strlen(hex) >= 8)
         {

src/Parsee/HMAC.c

@@ -0,0 +1,76 @@
+/* CC0 implementation of a HMAC system based on Cytoplasm.
+ * Ignore the scary "Parsee.h", its practically unused. */
+#include <Parsee.h>
+
+#include <Cytoplasm/Memory.h>
+#include <Cytoplasm/Sha.h>
+#include <Cytoplasm/Str.h>
+
+#include <string.h>
+
+/* A 64-byte key! */
+static uint8_t *
+ComputeKPad(char *key, uint8_t pad)
+{
+    size_t klen;
+    uint8_t *kp;
+    uint8_t *kopad;
+    size_t i;
+    if ((klen = strlen(key)) <= 64)
+    {
+        kp = Malloc(klen * sizeof(uint8_t));
+        memcpy(kp, key, klen);
+    }
+    else
+    {
+        kp = (uint8_t *) Sha256(key);
+        klen = 32;
+    }
+
+    /* Now that we have K', lets compute it XORd with opad */
+    kopad = Malloc(64 * sizeof(uint8_t));
+    for (i = 0; i < 64; i++)
+    {
+        uint8_t byte = i < klen ? kp[i] : 0x00;
+        kopad[i] = byte ^ pad;
+    }
+
+    Free(kp);
+    return kopad;
+}
+
+char *
+ParseeHMAC(char *key, uint8_t *msg, size_t msglen)
+{
+    uint8_t *opad, *ipad;
+    uint8_t *innersha;
+    uint8_t *outer;
+    unsigned char *sha;
+    char *str;
+    if (!key || !msg || !msglen)
+    {
+        return NULL;
+    }
+
+    opad = ComputeKPad(key, 0x5C);
+
+    ipad = ComputeKPad(key, 0x36);
+    ipad = Realloc(ipad, 64 + msglen);
+    memcpy(ipad + 64, msg, msglen);
+    innersha = Sha256Raw(ipad, 64 + msglen);
+
+    outer = Malloc(64 + 32);
+    memcpy(outer, opad, 64);
+    memcpy(outer + 64, innersha, 32);
+
+    sha = Sha256Raw(outer, 64 + 32);
+    str = ShaToHex(sha, HASH_SHA256);
+
+    Free(innersha);
+    Free(outer);
+    Free(ipad);
+    Free(opad);
+    Free(sha);
+
+    return str;
+}

src/Parsee/User.c

@@ -667,7 +667,8 @@ ParseeToUnauth(ParseeData *data, char *mxc)
 {
     Uri *url = NULL;
     char *ret;
-#define PAT "%s/_matrix/client/v1/media/download/%s%s"
+    char *key, *hmac;
+#define PAT "%s/_matrix/client/v1/media/download/%s%s?hmac=%s"
     size_t l;
     if (!data || !mxc)
     {
@@ -684,18 +685,25 @@ ParseeToUnauth(ParseeData *data, char *mxc)
         return NULL;
     }
 
+    key = StrConcat(2, url->host, url->path);
+    hmac = ParseeHMACS(data->id, key);
+    Free(key);
+
     l = snprintf(NULL, 0, 
         PAT,
         data->config->media_base, 
-        url->host, url->path
+        url->host, url->path,
+        hmac
     );
     ret = Malloc(l + 3);
     snprintf(ret, l + 1, 
         PAT,
         data->config->media_base, 
-        url->host, url->path
+        url->host, url->path,
+        hmac
     );
     UriFree(url);
+    Free(hmac);
     return ret;
 }
 

src/Routes/Media.c

@@ -2,27 +2,41 @@
 
 #include <Cytoplasm/Memory.h>
 #include <Cytoplasm/Str.h>
+#include <Cytoplasm/Log.h>
 
 #include <Matrix.h>
 #include <Parsee.h>
 #include <AS.h>
 
+#include <string.h>
+
 RouteHead(RouteMedia, arr, argp)
 {
     ParseeHttpArg *args = argp;
     HttpClientContext *cctx;
-    HashMap *reqh;
+    HashMap *reqh, *params;
     char *server = ArrayGet(arr, 0);
     char *identi = ArrayGet(arr, 1);
     char *path, *key, *val;
+    char *hmac, *chkmak = NULL;
+
+    params = HttpRequestParams(args->ctx);
+    hmac = HashMapGet(params, "hmac");
 
     /* TODO: Make it check the DB for its validicity. "Purging" would be useful.
      */
-    if (!server || !identi)
     {
+        char *concat = StrConcat(3, server, "/", identi);
+        chkmak = ParseeHMACS(args->data->id, concat);
+        Free(concat);
+    }
+    if (!server || !identi || !hmac || !StrEquals(hmac, chkmak))
+    {
+        Free(chkmak);
         HttpResponseStatus(args->ctx, HTTP_BAD_REQUEST);
         return MatrixCreateError("M_NOT_YET_UPLOADED", "No server/identifier");
     }
+    Free(chkmak);
     
     server = HttpUrlEncode(server);
     identi = HttpUrlEncode(identi);

src/include/Parsee.h

@@ -361,4 +361,12 @@ extern char * ParseeGenerateMTO(char *common_id);
  * Modifies: the Parsee config  */
 extern void ParseeSetThreads(int xmpp, int http);
 
+/** Computes an HMAC (with SHA-256) with a known key, and a generic message.
+ * --------------
+ * Returns: a hex representation of the HMAC[HEAP].
+ * Thrasher: Free
+ * Modifies: NOTHING */
+extern char * ParseeHMAC(char *key, uint8_t *msg, size_t msglen);
+#define ParseeHMACS(key, msg) ParseeHMAC(key, (uint8_t *) msg, strlen(msg))
+
 #endif