[rng] Add get_random_nz() function required by RSA algorithm

RSA requires the generation of random non-zero bytes (i.e. a sequence
of random numbers in the range [0x01,0xff]).  ANS X9.82 provides
various Approved methods for converting random bits into random
numbers.  The simplest such method is the Simple Discard Method.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/crypto/random_nz.c

@@ -0,0 +1,75 @@
+/*
+ * Copyright (C) 2012 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * 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 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., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+/** @file
+ *
+ * Random non-zero bytes
+ *
+ * The RSA algorithm requires the generation of random non-zero bytes,
+ * i.e. bytes in the range [0x01,0xff].
+ *
+ * This algorithm is designed to comply with ANS X9.82 Part 1-2006
+ * Section 9.2.1.  This standard is not freely available, but most of
+ * the text appears to be shared with NIST SP 800-90, which can be
+ * downloaded from
+ *
+ *     http://csrc.nist.gov/publications/nistpubs/800-90/SP800-90revised_March2007.pdf
+ *
+ * Where possible, references are given to both documents.  In the
+ * case of any disagreement, ANS X9.82 takes priority over NIST SP
+ * 800-90.  (In particular, note that some algorithms that are
+ * Approved by NIST SP 800-90 are not Approved by ANS X9.82.)
+ */
+
+#include <stddef.h>
+#include <stdint.h>
+#include <ipxe/rbg.h>
+#include <ipxe/random_nz.h>
+
+/**
+ * Get random non-zero bytes
+ *
+ * @v data		Output buffer
+ * @v len		Length of output buffer
+ * @ret rc		Return status code
+ *
+ * This algorithm is designed to be isomorphic to the Simple Discard
+ * Method described in ANS X9.82 Part 1-2006 Section 9.2.1 (NIST SP
+ * 800-90 Section B.5.1.1).
+ */
+int get_random_nz ( void *data, size_t len ) {
+	uint8_t *bytes = data;
+	int rc;
+
+	while ( len ) {
+
+		/* Generate random byte */
+		if ( ( rc = rbg_generate ( NULL, 0, 0, bytes, 1 ) ) != 0 )
+			return rc;
+
+		/* Move to next byte if this byte is acceptable */
+		if ( *bytes != 0 ) {
+			bytes++;
+			len--;
+		}
+	}
+
+	return 0;
+}

src/include/ipxe/random_nz.h

@@ -0,0 +1,16 @@
+#ifndef _IPXE_RANDOM_NZ_H
+#define _IPXE_RANDOM_NZ_H
+
+/** @file
+ *
+ * HMAC_DRBG algorithm
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+#include <stdint.h>
+
+extern int get_random_nz ( void *data, size_t len );
+
+#endif /* _IPXE_RANDOM_NZ_H */