[rng] Add ANS X9.82 Approved Hash_df derivation function

ANS X9.82 specifies several Approved derivation functions for use in
distributing entropy throughout a buffer.  One such derivation
function is Hash_df, which can be implemented using the existing iPXE
SHA-1 functionality.

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

src/crypto/hash_df.c

@@ -0,0 +1,134 @@
+/*
+ * 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
+ *
+ * Hash-based derivation function (Hash_df)
+ *
+ * This algorithm is designed to comply with ANS X9.82 Part 3-2007
+ * Section 10.5.2.  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 <stdint.h>
+#include <byteswap.h>
+#include <ipxe/crypto.h>
+#include <ipxe/hash_df.h>
+
+/**
+ * Distribute entropy throughout a buffer
+ *
+ * @v input		Input data
+ * @v input_len		Length of input data, in bytes
+ * @v output		Output buffer
+ * @v output_len	Length of output buffer, in bytes
+ *
+ * This is the Hash_df function defined in ANS X9.82 Part 3-2007
+ * Section 10.5.2 (NIST SP 800-90 Section 10.4.1).
+ *
+ * The number of bits requested is implicit in the length of the
+ * output buffer.  Requests must be for an integral number of bytes.
+ *
+ * The output buffer is filled incrementally with each iteration of
+ * the central loop, rather than constructing an overall "temp" and
+ * then taking the leftmost(no_of_bits_to_return) bits.
+ *
+ * There is no way for the Hash_df function to fail.  The returned
+ * status SUCCESS is implicit.
+ */
+void hash_df ( const void *input, size_t input_len, void *output,
+	      size_t output_len ) {
+	uint8_t context[HASH_DF_CTX_SIZE];
+	uint8_t digest[HASH_DF_OUTLEN_BYTES];
+	size_t frag_len;
+	struct {
+		uint8_t pad[3];
+		uint8_t counter;
+		uint32_t no_of_bits_to_return;
+	} __attribute__ (( packed )) prefix;
+	void *temp;
+	size_t remaining;
+
+	DBGC ( &hash_df, "HASH_DF input:\n" );
+	DBGC_HDA ( &hash_df, 0, input, input_len );
+
+	/* Sanity checks */
+	assert ( input != NULL );
+	assert ( output != NULL );
+
+	/* 1.  temp = the Null string
+	 * 2.  len = ceil ( no_of_bits_to_return / outlen )
+	 *
+	 * (Nothing to do.  We fill the output buffer incrementally,
+	 * rather than constructing the complete "temp" in-memory.
+	 * "len" is implicit in the number of iterations required to
+	 * fill the output buffer, and so is not calculated
+	 * explicitly.)
+	 */
+
+	/* 3.  counter = an 8-bit binary value representing the integer "1" */
+	prefix.counter = 1;
+
+	/* 4.  For i = 1 to len do */
+	for ( temp = output, remaining = output_len ; remaining > 0 ; ) {
+
+		/* Comment: in step 5.1 (sic), no_of_bits_to_return is
+		 * used as a 32-bit string.
+		 *
+		 * 4.1  temp = temp || Hash ( counter || no_of_bits_to_return
+		 *                            || input_string )
+		 */
+		prefix.no_of_bits_to_return = htonl ( output_len * 8 );
+		digest_init ( &hash_df_algorithm, context );
+		digest_update ( &hash_df_algorithm, context, &prefix.counter,
+				( sizeof ( prefix ) -
+				  offsetof ( typeof ( prefix ), counter ) ) );
+		digest_update ( &hash_df_algorithm, context, input, input_len );
+		digest_final ( &hash_df_algorithm, context, digest );
+
+		/* 4.2  counter = counter + 1 */
+		prefix.counter++;
+
+		/* 5.    requested_bits = Leftmost ( no_of_bits_to_return )
+		 *       of temp
+		 *
+		 * (We fill the output buffer incrementally.)
+		 */
+		frag_len = sizeof ( digest );
+		if ( frag_len > remaining )
+			frag_len = remaining;
+		memcpy ( temp, digest, frag_len );
+		temp += frag_len;
+		remaining -= frag_len;
+	}
+
+	/* 6.  Return SUCCESS and requested_bits */
+	DBGC ( &hash_df, "HASH_DF output:\n" );
+	DBGC_HDA ( &hash_df, 0, output, output_len );
+	return;
+}

src/include/ipxe/hash_df.h

@@ -0,0 +1,30 @@
+#ifndef _IPXE_HASH_DF_H
+#define _IPXE_HASH_DF_H
+
+/** @file
+ *
+ * Hash-based derivation function (Hash_df)
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+#include <stdint.h>
+#include <ipxe/sha1.h>
+
+/** Use SHA-1 as the underlying hash algorithm
+ *
+ * Hash_df using SHA-1 is an Approved algorithm in ANS X9.82.
+ */
+#define hash_df_algorithm sha1_algorithm
+
+/** Underlying hash algorithm output length (in bytes) */
+#define HASH_DF_OUTLEN_BYTES SHA1_DIGEST_SIZE
+
+/** Underlying hash algorithm context size (in bytes) */
+#define HASH_DF_CTX_SIZE SHA1_CTX_SIZE
+
+extern void hash_df ( const void *input, size_t input_len, void *output,
+		      size_t output_len );
+
+#endif /* _IPXE_HASH_DF_H */