Paul Eggert <[EMAIL PROTECTED]> writes:
> Some fairly minor comments:
>
> Simon Josefsson <[EMAIL PROTECTED]> writes:
>
>> +#define MOD256(n) ((n) & (ARCFOUR_SBOX_SIZE - 1))
>
> That is a strange name to use. I expected the definiens to be ((n) &
> 255). Why not use the name MOD_ARCFOUR_SBOX_SIZE, or some shorter
> variant perhaps?
>
> If the code going to say MOD256 elsewhere we might as well just
> open-code the &255 and dispense with the macro entirely.....
Actually, we'd might as well hard code '% ARCFOUR_SBOX_SIZE' and avoid
this issue. If we do this, the C code look like the algorithm
description in a text book, which is better than this likely remote
possibility of a speed improvement. A good compiler should be able to
optimize %256 into &255 if it make the code faster.
>> + register size_t i = context->idx_i;
>> + register size_t j = context->idx_j;
>
> These days there's no need for 'register'. Similarly for the
> other occurrences of 'register'. It just clutters up the code.
Removed.
>> + register char *sbox = context->sbox;
>
> For consistency, shouldn't arcfour_setkey also have this internal
> variable? (I doubt whether it'll affect the generated code, if
> optimization is enabled; it's just a style thing.)
Yup.
>> + i = MOD256(i + 1);
>> + j = MOD256(j + sbox[i]);
>
> GNU style suggests a space before the paren, even for macro calls.
> Similarly for the other occurrences of "MOD256(".
There is no macro now, so this doesn't apply any more.
>> +#define ARCFOUR_SBOX_SIZE 256
>> +
>> +typedef struct
>> +{
>> + size_t idx_i, idx_j;
>> + char sbox[ARCFOUR_SBOX_SIZE];
>> +} arcfour_context;
>
> Why must these be in arcfour.h? Shouldn't all this private to
> arcfour.c?
>
> You can replace the above lines with 'struct arcfour_context;' and
> then move them into arcfour.c (replacing 'arcfour_context' with
> 'struct arcfour_context' everywhere).
Like Bruno said, it should be possible to allocate the struct on the
stack, but more importantly, I think being able to access the sbox
values should be part of the public interface. The content of the
sbox/i/j state variables is fully specified, and some application may
find it useful to be able to access that data.
Revised patch below. Ok to install?
Thanks,
Simon
Index: ChangeLog
===================================================================
RCS file: /cvsroot/gnulib/gnulib/ChangeLog,v
retrieving revision 1.419
diff -u -p -r1.419 ChangeLog
--- ChangeLog 14 Oct 2005 00:59:45 -0000 1.419
+++ ChangeLog 14 Oct 2005 23:28:05 -0000
@@ -1,3 +1,9 @@
+2005-10-14 Simon Josefsson <[EMAIL PROTECTED]>
+
+ * tests/test-arcfour.c: New file.
+
+ * modules/arcfour, modules/arcfour-tests: New files.
+
2005-10-13 Oskar Liljeblad <[EMAIL PROTECTED]>
* modules/human (Depends-on): Depend on xstrtoumax, not xstrtol.
Index: modules/arcfour
===================================================================
RCS file: modules/arcfour
diff -N modules/arcfour
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ modules/arcfour 14 Oct 2005 23:28:05 -0000
@@ -0,0 +1,23 @@
+Description:
+ARCFOUR stream cipher implementation
+
+Files:
+lib/arcfour.h
+lib/arcfour.c
+m4/arcfour.m4
+
+Depends-on:
+
+configure.ac:
+gl_ARCFOUR
+
+Makefile.am:
+
+Include:
+"arcfour.h"
+
+License:
+LGPL
+
+Maintainer:
+Simon Josefsson
Index: modules/arcfour-tests
===================================================================
RCS file: modules/arcfour-tests
diff -N modules/arcfour-tests
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ modules/arcfour-tests 14 Oct 2005 23:28:05 -0000
@@ -0,0 +1,11 @@
+Files:
+tests/test-arcfour.c
+
+Depends-on:
+
+configure.ac:
+
+Makefile.am:
+TESTS += test-arcfour
+noinst_PROGRAMS += test-arcfour
+test_arcfour_SOURCES = test-arcfour.c
Index: m4/ChangeLog
===================================================================
RCS file: /cvsroot/gnulib/gnulib/m4/ChangeLog,v
retrieving revision 1.741
diff -u -p -r1.741 ChangeLog
--- m4/ChangeLog 13 Oct 2005 12:20:32 -0000 1.741
+++ m4/ChangeLog 14 Oct 2005 23:28:05 -0000
@@ -1,3 +1,7 @@
+2005-10-14 Simon Josefsson <[EMAIL PROTECTED]>
+
+ * arcfour.m4: New file.
+
2005-10-12 Bruno Haible <[EMAIL PROTECTED]>
* stdbool.m4 (gl_STDBOOL_H): Define as an alias of AM_STDBOOL_H.
Index: m4/arcfour.m4
===================================================================
RCS file: m4/arcfour.m4
diff -N m4/arcfour.m4
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ m4/arcfour.m4 14 Oct 2005 23:28:05 -0000
@@ -0,0 +1,11 @@
+# arcfour.m4 serial 1
+dnl Copyright (C) 2005 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+AC_DEFUN([gl_ARCFOUR],
+[
+ AC_LIBSOURCES([arcfour.c, arcfour.h])
+ AC_LIBOBJ([arcfour])
+])
Index: lib/ChangeLog
===================================================================
RCS file: /cvsroot/gnulib/gnulib/lib/ChangeLog,v
retrieving revision 1.1011
diff -u -p -r1.1011 ChangeLog
--- lib/ChangeLog 13 Oct 2005 07:49:05 -0000 1.1011
+++ lib/ChangeLog 14 Oct 2005 23:28:06 -0000
@@ -1,3 +1,7 @@
+2005-10-14 Simon Josefsson <[EMAIL PROTECTED]>
+
+ * arcfour.h, arcfour.c: New files.
+
2005-10-13 Simon Josefsson <[EMAIL PROTECTED]>
* gc-pbkdf2-sha1.c (gc_pbkdf2_sha1): Optimize CEIL computation.
Index: lib/arcfour.c
===================================================================
RCS file: lib/arcfour.c
diff -N lib/arcfour.c
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ lib/arcfour.c 14 Oct 2005 23:28:06 -0000
@@ -0,0 +1,79 @@
+/* arcfour.c --- The arcfour stream cipher
+ * Copyright (C) 2000, 2001, 2002, 2003, 2005 Free Software Foundation, Inc.
+ *
+ * This file 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, or (at your
+ * option) any later version.
+ *
+ * This file 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 file; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ *
+ */
+
+/* Code from Libgcrypt adapted for gnulib by Simon Josefsson. */
+
+/*
+ * For a description of the algorithm, see:
+ * Bruce Schneier: Applied Cryptography. John Wiley & Sons, 1996.
+ * ISBN 0-471-11709-9. Pages 397 ff.
+ */
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#include "arcfour.h"
+
+void
+arcfour_stream (arcfour_context * context, const char *inbuf, char *outbuf,
+ size_t length)
+{
+ size_t i = context->idx_i;
+ size_t j = context->idx_j;
+ char *sbox = context->sbox;
+
+ for (; length > 0; length--)
+ {
+ char t;
+
+ i = (i + 1) % ARCFOUR_SBOX_SIZE;
+ j = (j + sbox[i]) % ARCFOUR_SBOX_SIZE;
+ t = sbox[i];
+ sbox[i] = sbox[j];
+ sbox[j] = t;
+ *outbuf++ = *inbuf++ ^
+ sbox[(0U + sbox[i] + sbox[j]) % ARCFOUR_SBOX_SIZE];
+ }
+
+ context->idx_i = i;
+ context->idx_j = j;
+}
+
+void
+arcfour_setkey (arcfour_context * context, const char *key, size_t keylen)
+{
+ size_t i, j, k;
+ char *sbox = context->sbox;
+
+ context->idx_i = context->idx_j = 0;
+ for (i = 0; i < ARCFOUR_SBOX_SIZE; i++)
+ sbox[i] = i;
+ for (i = j = k = 0; i < ARCFOUR_SBOX_SIZE; i++)
+ {
+ char t;
+ j = (j + sbox[i] + key[k]) % ARCFOUR_SBOX_SIZE;
+ t = sbox[i];
+ sbox[i] = sbox[j];
+ sbox[j] = t;
+ if (++k == keylen)
+ k = 0;
+ }
+}
Index: lib/arcfour.h
===================================================================
RCS file: lib/arcfour.h
diff -N lib/arcfour.h
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ lib/arcfour.h 14 Oct 2005 23:28:06 -0000
@@ -0,0 +1,50 @@
+/* arcfour.h --- The arcfour stream cipher
+ * Copyright (C) 2000, 2001, 2002, 2003, 2004, 2005
+ * Free Software Foundation, Inc.
+ *
+ * This file 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, or (at your
+ * option) any later version.
+ *
+ * This file 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 file; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ *
+ */
+
+/* Code from Libgcrypt adapted for gnulib by Simon Josefsson. */
+
+#ifndef ARCFOUR_H
+# define ARCFOUR_H
+
+# include <stddef.h>
+
+#define ARCFOUR_SBOX_SIZE 256
+
+typedef struct
+{
+ size_t idx_i, idx_j;
+ char sbox[ARCFOUR_SBOX_SIZE];
+} arcfour_context;
+
+/* Apply ARCFOUR stream to INBUF placing the result in OUTBUF, both of
+ LENGTH size. CONTEXT must be initialized with arcfour_setkey
+ before this function is called. */
+extern void
+arcfour_stream (arcfour_context * context,
+ const char *inbuf, char *outbuf, size_t length);
+
+/* Initialize CONTEXT using encryption KEY of KEYLEN bytes. KEY
+ should be 40 bits (5 bytes) or longer. The KEY cannot be zero
+ length. */
+extern void
+arcfour_setkey (arcfour_context * context, const char *key, size_t keylen);
+
+#endif /* ARCFOUR_H */
Index: tests/test-arcfour.c
===================================================================
RCS file: tests/test-arcfour.c
diff -N tests/test-arcfour.c
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ tests/test-arcfour.c 14 Oct 2005 23:28:06 -0000
@@ -0,0 +1,73 @@
+/*
+ * Copyright (C) 2005 Free Software Foundation
+ * Written by Simon Josefsson
+ *
+ * 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, 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. */
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#include <stdio.h>
+#include <string.h>
+#include "arcfour.h"
+
+int
+main (int argc, char *argv[])
+{
+ arcfour_context ctx;
+ /* Test vector from Cryptlib via Libgcrypt labeled there: "from the
+ State/Commerce Department". */
+ static char key_1[] = { 0x61, 0x8A, 0x63, 0xD2, 0xFB };
+ static char plaintext_1[] = { 0xDC, 0xEE, 0x4C, 0xF9, 0x2C };
+ static const char ciphertext_1[] = { 0xF1, 0x38, 0x29, 0xC9, 0xDE };
+ char scratch[16];
+
+ arcfour_setkey (&ctx, key_1, sizeof (key_1));
+ arcfour_stream (&ctx, plaintext_1, scratch, sizeof (plaintext_1));
+ if (memcmp (scratch, ciphertext_1, sizeof (ciphertext_1)))
+ {
+ size_t i;
+ printf ("expected:\n");
+ for (i = 0; i < 5; i++)
+ printf ("%02x ", scratch[i] & 0xFF);
+ printf ("\ncomputed:\n");
+ for (i = 0; i < 5; i++)
+ printf ("%02x ", ciphertext_1[i] & 0xFF);
+ printf ("\n");
+ return 1;
+ }
+
+ /* decrypt */
+
+ arcfour_setkey (&ctx, key_1, sizeof (key_1));
+ arcfour_stream (&ctx, scratch, scratch, sizeof (plaintext_1));
+ if (memcmp (scratch, plaintext_1, sizeof (plaintext_1)))
+ {
+ size_t i;
+ printf ("expected:\n");
+ for (i = 0; i < 5; i++)
+ printf ("%02x ", plaintext_1[i] & 0xFF);
+ printf ("\ncomputed:\n");
+ for (i = 0; i < 5; i++)
+ printf ("%02x ", scratch[i] & 0xFF);
+ printf ("\n");
+ return 1;
+ }
+
+
+ return 0;
+}
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