New public function memeql_sec, declared in memops.h.

ChangeLog

@@ -43,6 +43,14 @@
 	* tools/nettle-pbkdf2.c (main): Fix some pointer signedness warning.
 	* tools/nettle-hash.c (hash_file): Likewise.
 
+	* examples/rsa-decrypt.c (process_file): Use memeql_sec to check
+	the digest.
+
+	* memeql-sec.c (memeql_sec): New public function, moved from...
+	* ccm.c (memeql_sec): ... previous location.
+
+	* memops.h: New header file, generalizing memxor.h.
+
 2016-08-29  Niels Möller  <nisse@lysator.liu.se>
 
 	* sexp-format.c (strlen_u8): New helper function.

Makefile.in

@@ -109,7 +109,7 @@ nettle_SOURCES = aes-decrypt-internal.c aes-decrypt.c \
 		 knuth-lfib.c \
 		 md2.c md2-meta.c md4.c md4-meta.c \
 		 md5.c md5-compress.c md5-compat.c md5-meta.c \
-		 memxor.c memxor3.c \
+		 memeql-sec.c memxor.c memxor3.c \
 		 nettle-meta-aeads.c nettle-meta-armors.c \
 		 nettle-meta-ciphers.c nettle-meta-hashes.c \
 		 pbkdf2.c pbkdf2-hmac-sha1.c pbkdf2-hmac-sha256.c \
@@ -193,7 +193,7 @@ HEADERS = aes.h arcfour.h arctwo.h asn1.h blowfish.h \
 	  macros.h \
 	  md2.h md4.h \
 	  md5.h md5-compat.h \
-	  memxor.h \
+	  memops.h memxor.h \
 	  nettle-meta.h nettle-types.h \
 	  pbkdf2.h \
 	  pgp.h pkcs1.h realloc.h ripemd160.h rsa.h \

ccm.c

@@ -44,7 +44,7 @@
 #include "ccm.h"
 #include "ctr.h"
 
-#include "memxor.h"
+#include "memops.h"
 #include "nettle-internal.h"
 #include "macros.h"
 
@@ -246,19 +246,6 @@ ccm_encrypt_message(const void *cipher, nettle_cipher_func *f,
   ccm_digest(&ctx, cipher, f, tlength, tag);
 }
 
-/* FIXME: Should be made public, under some suitable name. */
-static int
-memeql_sec (const void *a, const void *b, size_t n)
-{
-  volatile const unsigned char *ap = (const unsigned char *) a;
-  volatile const unsigned char *bp = (const unsigned char *) b;
-  volatile unsigned char d;
-  size_t i;
-  for (d = i = 0; i < n; i++)
-    d |= (ap[i] ^ bp[i]);
-  return d == 0;
-}
-
 int
 ccm_decrypt_message(const void *cipher, nettle_cipher_func *f,
 		    size_t nlength, const uint8_t *nonce,

examples/rsa-decrypt.c

@@ -49,6 +49,7 @@
 #include "cbc.h"
 #include "hmac.h"
 #include "macros.h"
+#include "memops.h"
 #include "rsa.h"
 #include "yarrow.h"
 
@@ -189,7 +190,7 @@ process_file(struct rsa_session *ctx,
 	}
     }
   hmac_sha1_digest(&ctx->hmac, SHA1_DIGEST_SIZE, digest);
-  if (memcmp(digest, buffer + AES_BLOCK_SIZE, SHA1_DIGEST_SIZE) != 0)
+  if (!memeql_sec(digest, buffer + AES_BLOCK_SIZE, SHA1_DIGEST_SIZE))
     {
       werror("Decryption failed: Invalid mac.\n");
       return 0;

memeql-sec.c

+/* memeql-sec.c
+
+   Copyright (C) 2016 Niels Möller
+
+   This file is part of GNU Nettle.
+
+   GNU Nettle is free software: you can redistribute it and/or
+   modify it under the terms of either:
+
+     * the GNU Lesser General Public License as published by the Free
+       Software Foundation; either version 3 of the License, or (at your
+       option) any later version.
+
+   or
+
+     * the GNU General Public License as published by the Free
+       Software Foundation; either version 2 of the License, or (at your
+       option) any later version.
+
+   or both in parallel, as here.
+
+   GNU Nettle is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received copies of the GNU General Public License and
+   the GNU Lesser General Public License along with this program.  If
+   not, see http://www.gnu.org/licenses/.
+*/
+
+#if HAVE_CONFIG_H
+# include "config.h"
+#endif
+
+#include "memops.h"
+
+int
+memeql_sec (const void *a, const void *b, size_t n)
+{
+  volatile const unsigned char *ap = (const unsigned char *) a;
+  volatile const unsigned char *bp = (const unsigned char *) b;
+
+  volatile unsigned char diff;
+  size_t i;
+
+  for (i = diff = 0; i < n; i++)
+    diff |= (ap[i] ^ bp[i]);
+
+  return diff == 0;
+}

memops.h

+/* memops.h
+
+   Copyright (C) 2016 Niels Möller
+
+   This file is part of GNU Nettle.
+
+   GNU Nettle is free software: you can redistribute it and/or
+   modify it under the terms of either:
+
+     * the GNU Lesser General Public License as published by the Free
+       Software Foundation; either version 3 of the License, or (at your
+       option) any later version.
+
+   or
+
+     * the GNU General Public License as published by the Free
+       Software Foundation; either version 2 of the License, or (at your
+       option) any later version.
+
+   or both in parallel, as here.
+
+   GNU Nettle is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received copies of the GNU General Public License and
+   the GNU Lesser General Public License along with this program.  If
+   not, see http://www.gnu.org/licenses/.
+*/
+
+#ifndef NETTLE_MEMOPS_H_INCLUDED
+#define NETTLE_MEMOPS_H_INCLUDED
+
+#include "memxor.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* Name mangling */
+#define memeql_sec nettle_memeql_sec
+
+int
+memeql_sec (const void *a, const void *b, size_t n);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* NETTLE_MEMOPS_H_INCLUDED */