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https://github.com/ipxe/ipxe
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cfbf0da93c
ECDSA requires the ability to add two arbitrary curve points, either of which may legitimately be the point at infinity. Update the API so that curves must choose an explicit affine representation for the point at infinity, and provide a method to test for this representation. Multiplication and addition will now allow this representation to be provided as an input, and will not fail if the result is the point at infinity. Callers must explicitly check for the point at infinity where needed (e.g. after computing the ECDHE shared secret curve point). Signed-off-by: Michael Brown <mcb30@ipxe.org>
75 lines
2.2 KiB
C
75 lines
2.2 KiB
C
/*
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* Copyright (C) 2025 Michael Brown <mbrown@fensystems.co.uk>.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation; either version 2 of the
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* License, or any later version.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
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* 02110-1301, USA.
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*
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* You can also choose to distribute this program under the terms of
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* the Unmodified Binary Distribution Licence (as given in the file
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* COPYING.UBDL), provided that you have satisfied its requirements.
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*/
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FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
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/** @file
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*
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* Elliptic Curve Ephemeral Diffie-Hellman (ECDHE) key exchange
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*
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*/
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#include <string.h>
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#include <errno.h>
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#include <ipxe/ecdhe.h>
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/**
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* Calculate ECDHE key
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*
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* @v curve Elliptic curve
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* @v partner Partner public curve point
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* @v private Private key
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* @v public Public curve point to fill in (may overlap partner key)
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* @v shared Shared secret curve point to fill in
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* @ret rc Return status code
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*/
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int ecdhe_key ( struct elliptic_curve *curve, const void *partner,
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const void *private, void *public, void *shared ) {
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int rc;
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/* Construct shared key */
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if ( ( rc = elliptic_multiply ( curve, partner, private,
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shared ) ) != 0 ) {
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DBGC ( curve, "CURVE %s could not generate shared key: %s\n",
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curve->name, strerror ( rc ) );
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return rc;
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}
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/* Construct public key */
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if ( ( rc = elliptic_multiply ( curve, curve->base, private,
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public ) ) != 0 ) {
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DBGC ( curve, "CURVE %s could not generate public key: %s\n",
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curve->name, strerror ( rc ) );
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return rc;
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}
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/* Check that partner and shared keys are not the point at infinity */
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if ( elliptic_is_infinity ( curve, shared ) ) {
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DBGC ( curve, "CURVE %s constructed point at infinity\n",
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curve->name );
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return -EPERM;
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}
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return 0;
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}
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