Provide internal ARC4 implementation

Now you can build bittorrent support without without external
libraries, meaning you can skip libnettle, libgmp, libgcrypt, GnuTLS and
OpenSSL on OSX (for now).

configure.ac

@@ -518,12 +518,13 @@ fi
 if test "x$have_libnettle" = "xyes" ||
    test "x$have_libgcrypt" = "xyes" ||
    test "x$have_openssl" = "xyes"; then
-  have_rc4=yes
+  AM_CONDITIONAL([USE_INTERNAL_ARC4], false)
+else
+  AC_DEFINE([USE_INTERNAL_ARC4], [1], [Define to 1 if internal ARC4 support is enabled.])
+  AM_CONDITIONAL([USE_INTERNAL_ARC4], true)
 fi
 
-
 if test "x$enable_bittorrent" = "xyes" &&
-   test "x$have_rc4" = "xyes" &&
    test "x$enable_message_digest" = "xyes"; then
   AC_DEFINE([ENABLE_BITTORRENT], [1],
             [Define to 1 if BitTorrent support is enabled.])

src/ARC4Encryptor.h

@@ -36,31 +36,15 @@
 #define D_ARC4_ENCRYPTOR_H
 
 #include "common.h"
-#ifdef HAVE_LIBNETTLE
+
+#ifdef USE_INTERNAL_ARC4
+# include "InternalARC4Encryptor.h"
+#elif HAVE_LIBNETTLE
 # include "LibnettleARC4Encryptor.h"
 #elif HAVE_LIBGCRYPT
 # include "LibgcryptARC4Encryptor.h"
 #elif HAVE_OPENSSL
 # include "LibsslARC4Encryptor.h"
-#else
-
-// provide empty implementation to compile sources without both libgcrypt and
-// openssl installed
-namespace aria2 {
-
-class ARC4Encryptor {
-public:
-  ARC4Encryptor() {}
-
-  ~ARC4Encryptor() {}
-
-  void init(const unsigned char* key, size_t keyLength) {}
-
-  void encrypt(size_t len, unsigned char* out, const unsigned char* in);
-};
-
-} // namespace aria2
-
 #endif
 
 #endif // D_ARC4_ENCRYPTOR_H

src/InternalARC4Encryptor.cc

@@ -0,0 +1,73 @@
+/* <!-- copyright */
+/*
+ * aria2 - The high speed download utility
+ *
+ * Copyright (C) 2013 Nils Maier
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of 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.
+ *
+ * This program 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 a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ *
+ * In addition, as a special exception, the copyright holders give
+ * permission to link the code of portions of this program with the
+ * OpenSSL library under certain conditions as described in each
+ * individual source file, and distribute linked combinations
+ * including the two.
+ * You must obey the GNU General Public License in all respects
+ * for all of the code used other than OpenSSL.  If you modify
+ * file(s) with this exception, you may extend this exception to your
+ * version of the file(s), but you are not obligated to do so.  If you
+ * do not wish to do so, delete this exception statement from your
+ * version.  If you delete this exception statement from all source
+ * files in the program, then also delete it here.
+ */
+/* copyright --> */
+
+#include "InternalARC4Encryptor.h"
+
+namespace aria2 {
+
+ARC4Encryptor::~ARC4Encryptor()
+{
+  for (auto& c : state_) c = 0;
+  i = j = 0;
+}
+void ARC4Encryptor::init(const unsigned char* key, size_t keyLength)
+{
+  j = 0;
+  for (auto& c : state_) c = j++;
+
+  j = 0;
+  for (i = 0; i < sizeof(state_); ++i) {
+    j = (j + state_[i] + key[i % keyLength]) & 0xff;
+    auto tmp = state_[i];
+    state_[i] = state_[j];
+    state_[j] = tmp;
+  }
+  i = j = 0;
+}
+
+void ARC4Encryptor::encrypt(size_t len, unsigned char* out,
+                            const unsigned char* in)
+{
+  for (auto c = 0; c < len; ++c) {
+    i = (i + 1) & 0xff;
+    j = (j + state_[i]) & 0xff;
+    auto sj = state_[i];
+    auto si = state_[i] = state_[j];
+    state_[j] = sj;
+    out[c] = in[c] ^ state_[(si + sj) & 0xff];
+  }
+}
+
+} // namespace aria2

src/InternalARC4Encryptor.h

@@ -0,0 +1,60 @@
+/* <!-- copyright */
+/*
+ * aria2 - The high speed download utility
+ *
+ * Copyright (C) 2013 Nils Maier
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of 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.
+ *
+ * This program 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 a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ *
+ * In addition, as a special exception, the copyright holders give
+ * permission to link the code of portions of this program with the
+ * OpenSSL library under certain conditions as described in each
+ * individual source file, and distribute linked combinations
+ * including the two.
+ * You must obey the GNU General Public License in all respects
+ * for all of the code used other than OpenSSL.  If you modify
+ * file(s) with this exception, you may extend this exception to your
+ * version of the file(s), but you are not obligated to do so.  If you
+ * do not wish to do so, delete this exception statement from your
+ * version.  If you delete this exception statement from all source
+ * files in the program, then also delete it here.
+ */
+/* copyright --> */
+#ifndef D_INTERNAL_ARC4_ENCRYPTOR_H
+#define D_INTERNAL_ARC4_ENCRYPTOR_H
+
+#include "common.h"
+
+namespace aria2 {
+
+class ARC4Encryptor {
+private:
+  unsigned char state_[256];
+  unsigned i, j;
+
+public:
+  ARC4Encryptor() {}
+  ~ARC4Encryptor();
+
+  void init(const unsigned char* key, size_t keyLength);
+
+  // Encrypts data in in buffer to out buffer. in and out can be the
+  // same buffer.
+  void encrypt(size_t len, unsigned char* out, const unsigned char* in);
+};
+
+} // namespace aria2
+
+#endif // D_INTERNAL_ARC4_ENCRYPTOR_H

src/Makefile.am

@@ -337,6 +337,10 @@ if USE_INTERNAL_BIGNUM
 SRCS += InternalDHKeyExchange.cc InternalDHKeyExchange.h bignum.h
 endif
 
+if USE_INTERNAL_ARC4
+SRCS += InternalARC4Encryptor.cc InternalARC4Encryptor.h
+endif
+
 if USE_INTERNAL_MD
 SRCS += InternalMessageDigestImpl.cc sha1.c md5.c
 endif # USE_WINDOWS_MD

test/ARC4Test.cc

@@ -37,14 +37,16 @@ void ARC4Test::testEncrypt()
 
   unsigned char encrypted[LEN];
   unsigned char decrypted[LEN];
+
   enc.encrypt(LEN, encrypted, key);
+  CPPUNIT_ASSERT(memcmp(key, encrypted, LEN) != 0);
   dec.encrypt(LEN, decrypted, encrypted);
-
   CPPUNIT_ASSERT(memcmp(key, decrypted, LEN) == 0);
+
   // once more
   enc.encrypt(LEN, encrypted, key);
+  CPPUNIT_ASSERT(memcmp(key, encrypted, LEN) != 0);
   dec.encrypt(LEN, decrypted, encrypted);
-
   CPPUNIT_ASSERT(memcmp(key, decrypted, LEN) == 0);
 }