From f50ae72ec3417cae55dd4e085991c01af9fdc5f1 Mon Sep 17 00:00:00 2001
From: Martin Nagy <mnagy@redhat.com>
Date: Wed, 11 Feb 2009 20:37:59 +0100
Subject: Initial commit

---
 lib/isc/include/isc/lfsr.h | 130 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 130 insertions(+)
 create mode 100644 lib/isc/include/isc/lfsr.h

(limited to 'lib/isc/include/isc/lfsr.h')

diff --git a/lib/isc/include/isc/lfsr.h b/lib/isc/include/isc/lfsr.h
new file mode 100644
index 0000000..d4d9707
--- /dev/null
+++ b/lib/isc/include/isc/lfsr.h
@@ -0,0 +1,130 @@
+/*
+ * Copyright (C) 2004-2007  Internet Systems Consortium, Inc. ("ISC")
+ * Copyright (C) 1999-2001  Internet Software Consortium.
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
+ * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
+ * AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
+ * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
+ * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
+ * OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+ * PERFORMANCE OF THIS SOFTWARE.
+ */
+
+/* $Id: lfsr.h,v 1.17 2007/06/19 23:47:18 tbox Exp $ */
+
+#ifndef ISC_LFSR_H
+#define ISC_LFSR_H 1
+
+/*! \file isc/lfsr.h */
+
+#include <isc/lang.h>
+#include <isc/types.h>
+
+typedef struct isc_lfsr isc_lfsr_t;
+
+/*%
+ * This function is called when reseeding is needed.  It is allowed to
+ * modify any state in the LFSR in any way it sees fit OTHER THAN "bits".
+ *
+ * It MUST set "count" to a new value or the lfsr will never reseed again.
+ *
+ * Also, a reseed will never occur in the middle of an extraction.  This
+ * is purely an optimization, and is probably what one would want.
+ */
+typedef void (*isc_lfsrreseed_t)(isc_lfsr_t *, void *);
+
+/*%
+ * The members of this structure can be used by the application, but care
+ * needs to be taken to not change state once the lfsr is in operation.
+ */
+struct isc_lfsr {
+	isc_uint32_t		state;	/*%< previous state */
+	unsigned int		bits;	/*%< length */
+	isc_uint32_t		tap;	/*%< bit taps */
+	unsigned int		count;	/*%< reseed count (in BITS!) */
+	isc_lfsrreseed_t	reseed;	/*%< reseed function */
+	void		       *arg;	/*%< reseed function argument */
+};
+
+ISC_LANG_BEGINDECLS
+
+
+void 
+isc_lfsr_init(isc_lfsr_t *lfsr, isc_uint32_t state, unsigned int bits,
+		   isc_uint32_t tap, unsigned int count,
+		   isc_lfsrreseed_t reseed, void *arg);
+/*%<
+ * Initialize an LFSR.
+ *
+ * Note:
+ *
+ *\li	Putting untrusted values into this function will cause the LFSR to
+ *	generate (perhaps) non-maximal length sequences.
+ *
+ * Requires:
+ *
+ *\li	lfsr != NULL
+ *
+ *\li	8 <= bits <= 32
+ *
+ *\li	tap != 0
+ */
+
+void 
+isc_lfsr_generate(isc_lfsr_t *lfsr, void *data, unsigned int count);
+/*%<
+ * Returns "count" bytes of data from the LFSR.
+ *
+ * Requires:
+ *
+ *\li	lfsr be valid.
+ *
+ *\li	data != NULL.
+ *
+ *\li	count > 0.
+ */
+
+void 
+isc_lfsr_skip(isc_lfsr_t *lfsr, unsigned int skip);
+/*%<
+ * Skip "skip" states.
+ *
+ * Requires:
+ *
+ *\li	lfsr be valid.
+ */
+
+isc_uint32_t 
+isc_lfsr_generate32(isc_lfsr_t *lfsr1, isc_lfsr_t *lfsr2);
+/*%<
+ * Given two LFSRs, use the current state from each to skip entries in the
+ * other.  The next states are then xor'd together and returned.
+ *
+ * WARNING:
+ *
+ *\li	This function is used only for very, very low security data, such
+ *	as DNS message IDs where it is desired to have an unpredictable
+ *	stream of bytes that are harder to predict than a simple flooding
+ *	attack.
+ *
+ * Notes:
+ *
+ *\li	Since the current state from each of the LFSRs is used to skip
+ *	state in the other, it is important that no state be leaked
+ *	from either LFSR.
+ *
+ * Requires:
+ *
+ *\li	lfsr1 and lfsr2 be valid.
+ *
+ *\li	1 <= skipbits <= 31
+ */
+
+ISC_LANG_ENDDECLS
+
+#endif /* ISC_LFSR_H */
-- 
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