--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+2005-10-14  Simon Josefsson  <jas@extundo.com>
+
+	* tests/test-arcfour.c: New file.
+
+	* modules/arcfour, modules/arcfour-tests: New files.
+
 2005-10-13  Oskar Liljeblad  <oskar@osk.mine.nu>
 
         * modules/human (Depends-on): Depend on xstrtoumax, not xstrtol.

--- a/lib/ChangeLog
+++ b/lib/ChangeLog
@@ -1,3 +1,7 @@
+2005-10-14  Simon Josefsson  <jas@extundo.com>
+
+	* arcfour.h, arcfour.c: New files.
+
 2005-10-14  Paul Eggert  <eggert@cs.ucla.edu>
 
 	* obstack.c [defined _LIBC && defined USE_IN_LIBIO]: Don't

new file mode 100644
--- /dev/null
+++ b/lib/arcfour.c
@@ -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;
+    }
+}

new file mode 100644
--- /dev/null
+++ b/lib/arcfour.h
@@ -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 */

--- a/m4/ChangeLog
+++ b/m4/ChangeLog
@@ -1,3 +1,7 @@
+2005-10-14  Simon Josefsson  <jas@extundo.com>
+
+	* arcfour.m4: New file.
+
 2005-10-12  Bruno Haible  <bruno@clisp.org>
 
 	* stdbool.m4 (gl_STDBOOL_H): Define as an alias of AM_STDBOOL_H.

new file mode 100644
--- /dev/null
+++ b/m4/arcfour.m4
@@ -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])
+])

new file mode 100644
--- /dev/null
+++ b/modules/arcfour
@@ -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

new file mode 100644
--- /dev/null
+++ b/modules/arcfour-tests
@@ -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

new file mode 100644
--- /dev/null
+++ b/tests/test-arcfour.c
@@ -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;
+}