using constant time memcmp by C.Meessen

ChangeLog

@@ -18,6 +18,10 @@ NEXT
 	so, pcp aims to be secure by default and fails
 	safely.
 
+	Using cst_time_memcpy by Christophe Meessen instead
+	of libc's memcpy: constant time memcpy is much more
+	secure than the default, especially in our context.
+
 0.3.0
 	Changed publuc key signature storage, previously
 	I didn't add the actual signature, therefore a

INSTALL

@@ -1,7 +1,7 @@
 Installation Instructions
 *************************
 
-Copyright (C) 1994-1996, 1999-2002, 2004-2012 Free Software Foundation,
+Copyright (C) 1994-1996, 1999-2002, 2004-2013 Free Software Foundation,
 Inc.
 
    Copying and distribution of this file, with or without modification,
@@ -12,8 +12,8 @@ without warranty of any kind.
 Basic Installation
 ==================
 
-   Briefly, the shell commands `./configure; make; make install' should
+   Briefly, the shell command `./configure && make && make install'
-configure, build, and install this package.  The following
+should configure, build, and install this package.  The following
 more-detailed instructions are generic; see the `README' file for
 instructions specific to this package.  Some packages provide this
 `INSTALL' file but do not implement all of the features documented

include/pcp/config.h.in

@@ -160,9 +160,6 @@
    */
 #undef LT_OBJDIR
 
-/* Define to 1 if your C compiler doesn't accept -c and -o together. */
-#undef NO_MINUS_C_MINUS_O
-
 /* Name of package */
 #undef PACKAGE
 

include/pcp/util.h

@@ -115,6 +115,14 @@ char *_bin2hex(byte *bin, size_t len);
 */
 size_t _hex2bin(const char *hex_str, unsigned char *byte_array, size_t byte_array_max);
 
+/** compare two memory regions in a constant time
+    \param[in] m1 array1
+    \param[in] m2 array2
+    \param[in] n size in bytes to compare
+    \return 0 if m1 and m2 are equal up to n
+ */
+int cst_time_memcmp(const void *m1, const void *m2, size_t n);
+
 #endif /*  _HAVE_PCP_UTIL_H */
 
 /**@}*/

libpcp/crypto.c

@@ -614,7 +614,7 @@ size_t pcp_decrypt_stream_sym(PCPCTX *ptx, Pcpstream *in, Pcpstream* out, byte *
       if(verifiedhash == NULL)
 	out_size = 0;
       else {
-	if(memcmp(verifiedhash, hash, crypto_generichash_BYTES_MAX) != 0) {
+	if(cst_time_memcmp(verifiedhash, hash, crypto_generichash_BYTES_MAX) != 0) {
 	  /*  sig verified, but the hash doesn't match */	
 	  fatal(ptx, "signed hash doesn't match actual hash of signed decrypted file content\n");
 	  out_size = 0;

libpcp/ed.c

@@ -301,7 +301,7 @@ pcp_pubkey_t *pcp_ed_verify_buffered(PCPCTX *ptx, Pcpstream *in, pcp_pubkey_t *p
   if(verifiedhash == NULL)
     goto errvb1;
 
-  if(memcmp(verifiedhash, hash, crypto_generichash_BYTES_MAX) != 0) {
+  if(cst_time_memcmp(verifiedhash, hash, crypto_generichash_BYTES_MAX) != 0) {
     /*  sig verified, but the hash doesn't */
     fatal(ptx, "signed hash doesn't match actual hash of signed file content\n");
     free(verifiedhash);
@@ -441,7 +441,7 @@ pcp_pubkey_t *pcp_ed_detachverify_buffered(PCPCTX *ptx, Pcpstream *in, Pcpstream
   if(verifiedhash == NULL)
     goto errdea4;
 
-  if(memcmp(verifiedhash, hash, crypto_generichash_BYTES_MAX) != 0) {
+  if(cst_time_memcmp(verifiedhash, hash, crypto_generichash_BYTES_MAX) != 0) {
     /*  sig verified, but the hash doesn't */
     fatal(ptx, "signed hash doesn't match actual hash of signed file content\n");
     goto errdea5;

libpcp/mgmt.c

@@ -181,7 +181,7 @@ int _check_hash_keysig(PCPCTX *ptx, Buffer *blob, pcp_pubkey_t *p, pcp_keysig_t
   crypto_generichash_final(st, hash, crypto_generichash_BYTES_MAX);
 
   /* compare them */
-  if(memcmp(hash, verifyhash, crypto_generichash_BYTES_MAX) != 0) {
+  if(cst_time_memcmp(hash, verifyhash, crypto_generichash_BYTES_MAX) != 0) {
     fatal(ptx, "Signature verifies but signed hash doesn't match signature contents\n");
     goto chker2;
   }

libpcp/util.c

@@ -119,3 +119,46 @@ size_t _hex2bin(const char *hex_str, unsigned char *byte_array, size_t byte_arra
 
     return byte_array_size;
 }
+
+/* via https://github.com/chmike/cst_time_memcmp
+
+Licensed as:
+
+The MIT License (MIT)
+
+Copyright (c) 2015 Christophe Meessen
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+
+This is the safest1 variant using subscriptions.
+
+*/
+int cst_time_memcmp(const void *m1, const void *m2, size_t n) {
+  int res = 0, diff;
+  if (m1 != m2 && n && m1 && m2) {
+    const unsigned char *pm1 = (const unsigned char *)m1;
+    const unsigned char *pm2 = (const unsigned char *)m2;
+    do {
+      --n;
+      diff = pm1[n] - pm2[n];
+      res = (res & (((diff - 1) & ~diff) >> 8)) | diff;
+    } while (n != 0);
+  }
+  return ((res - 1) >> 8) + (res >> 8) + 1;
+}

libpcp/vault.c

@@ -522,7 +522,7 @@ int pcpvault_fetchall(PCPCTX *ptx, vault_t *vault) {
   
   if(pcphash_count(ptx) + pcphash_countpub(ptx) > 0) {
     /*  only validate the checksum if there are keys */
-    if(memcmp(checksum, vault->checksum, LSHA) != 0) {
+    if(cst_time_memcmp(checksum, vault->checksum, LSHA) != 0) {
       fatal(ptx, "Error: the checksum of the key vault doesn't match its contents!\n");
       goto err;
     }