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[crypto] Add implementation of MS-CHAPv2 authentication
Add an implementation of the authentication portions of the MS-CHAPv2 algorithm as defined in RFC 2759, along with the single test vector provided therein. Signed-off-by: Michael Brown <mcb30@ipxe.org>
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Michael Brown
363
src/crypto/mschapv2.c
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363
src/crypto/mschapv2.c
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/*
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* Copyright (C) 2024 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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* MS-CHAPv2 authentication
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*
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* The algorithms used for MS-CHAPv2 authentication are defined in
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* RFC 2759 section 8.
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*/
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#include <stdio.h>
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#include <string.h>
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#include <byteswap.h>
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#include <ipxe/md4.h>
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#include <ipxe/sha1.h>
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#include <ipxe/des.h>
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#include <ipxe/mschapv2.h>
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/**
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* MS-CHAPv2 context block
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*
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* For no particularly discernible reason, MS-CHAPv2 uses two
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* different digest algorithms and one block cipher. The uses do not
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* overlap, so share the context storage between these to reduce stack
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* usage.
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*/
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union mschapv2_context {
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/** SHA-1 digest context */
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uint8_t sha1[SHA1_CTX_SIZE];
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/** MD4 digest context */
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uint8_t md4[MD4_CTX_SIZE];
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/** DES cipher context */
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uint8_t des[DES_CTX_SIZE];
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};
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/**
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* MS-CHAPv2 challenge hash
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*
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* MS-CHAPv2 calculates the SHA-1 digest of the peer challenge, the
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* authenticator challenge, and the username, and then uses only the
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* first 8 bytes of the result (as a DES plaintext block).
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*/
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union mschapv2_challenge_hash {
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/** SHA-1 digest */
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uint8_t sha1[SHA1_DIGEST_SIZE];
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/** DES plaintext block */
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uint8_t des[DES_BLOCKSIZE];
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};
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/**
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* MS-CHAPv2 password hash
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*
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* MS-CHAPv2 calculates the MD4 digest of an unspecified two-byte
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* little-endian Unicode encoding (presumably either UCS-2LE or
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* UTF-16LE) of the password.
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*
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* For constructing the challenge response, the MD4 digest is then
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* zero-padded to 21 bytes and used as three separate 56-bit DES keys.
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*
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* For constructing the authenticator response, the MD4 digest is then
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* used as an input to a SHA-1 digest along with the NT response and a
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* magic constant.
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*/
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union mschapv2_password_hash {
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/** MD4 digest */
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uint8_t md4[MD4_DIGEST_SIZE];
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/** SHA-1 digest */
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uint8_t sha1[SHA1_DIGEST_SIZE];
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/** DES keys */
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uint8_t des[3][DES_BLOCKSIZE];
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/** DES key expansion */
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uint8_t expand[ 3 * DES_BLOCKSIZE ];
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};
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/** MS-CHAPv2 magic constant 1 */
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static const char mschapv2_magic1[39] =
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"Magic server to client signing constant";
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/** MS-CHAPv2 magic constant 2 */
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static const char mschapv2_magic2[41] =
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"Pad to make it do more than one iteration";
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/**
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* Calculate MS-CHAPv2 challenge hash
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*
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* @v ctx Context block
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* @v challenge Authenticator challenge
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* @v peer Peer challenge
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* @v username User name (or NULL to use empty string)
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* @v chash Challenge hash to fill in
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*
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* This is the ChallengeHash() function as documented in RFC 2759
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* section 8.2.
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*/
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static void
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mschapv2_challenge_hash ( union mschapv2_context *ctx,
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const struct mschapv2_challenge *challenge,
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const struct mschapv2_challenge *peer,
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const char *username,
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union mschapv2_challenge_hash *chash ) {
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struct digest_algorithm *sha1 = &sha1_algorithm;
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/* Calculate SHA-1 hash of challenges and username */
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digest_init ( sha1, ctx->sha1 );
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digest_update ( sha1, ctx->sha1, peer, sizeof ( *peer ) );
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digest_update ( sha1, ctx->sha1, challenge, sizeof ( *challenge ) );
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if ( username ) {
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digest_update ( sha1, ctx->sha1, username,
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strlen ( username ) );
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}
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digest_final ( sha1, ctx->sha1, chash->sha1 );
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DBGC ( ctx, "MSCHAPv2 authenticator challenge:\n" );
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DBGC_HDA ( ctx, 0, challenge, sizeof ( *challenge ) );
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DBGC ( ctx, "MSCHAPv2 peer challenge:\n" );
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DBGC_HDA ( ctx, 0, peer, sizeof ( *peer ) );
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DBGC ( ctx, "MSCHAPv2 challenge hash:\n" );
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DBGC_HDA ( ctx, 0, chash->des, sizeof ( chash->des ) );
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}
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/**
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* Calculate MS-CHAPv2 password hash
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*
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* @v ctx Context block
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* @v password Password (or NULL to use empty string)
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* @v phash Password hash to fill in
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*
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* This is the NtPasswordHash() function as documented in RFC 2759
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* section 8.3.
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*/
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static void mschapv2_password_hash ( union mschapv2_context *ctx,
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const char *password,
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union mschapv2_password_hash *phash ) {
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struct digest_algorithm *md4 = &md4_algorithm;
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uint16_t wc;
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uint8_t c;
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/* Construct zero-padded MD4 hash of encoded password */
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memset ( phash, 0, sizeof ( *phash ) );
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digest_init ( md4, ctx->md4 );
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if ( password ) {
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while ( ( c = *(password++) ) ) {
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wc = cpu_to_le16 ( c );
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digest_update ( md4, ctx->md4, &wc, sizeof ( wc ) );
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}
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}
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digest_final ( md4, ctx->md4, phash->md4 );
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DBGC ( ctx, "MSCHAPv2 password hash:\n" );
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DBGC_HDA ( ctx, 0, phash->md4, sizeof ( phash->md4 ) );
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}
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/**
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* Hash the MS-CHAPv2 password hash
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*
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* @v ctx Context block
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* @v phash Password hash to be rehashed
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*
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* This is the HashNtPasswordHash() function as documented in RFC 2759
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* section 8.4.
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*/
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static void mschapv2_hash_hash ( union mschapv2_context *ctx,
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union mschapv2_password_hash *phash ) {
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struct digest_algorithm *md4 = &md4_algorithm;
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/* Calculate MD4 hash of existing MD4 hash */
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digest_init ( md4, ctx->md4 );
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digest_update ( md4, ctx->md4, phash->md4, sizeof ( phash->md4 ) );
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digest_final ( md4, ctx->md4, phash->md4 );
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DBGC ( ctx, "MSCHAPv2 password hash hash:\n" );
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DBGC_HDA ( ctx, 0, phash->md4, sizeof ( phash->md4 ) );
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}
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/**
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* Expand MS-CHAPv2 password hash by inserting DES dummy parity bits
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*
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* @v ctx Context block
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* @v phash Password hash to expand
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*
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* This is part of the DesEncrypt() function as documented in RFC 2759
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* section 8.6.
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*/
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static void mschapv2_expand_hash ( union mschapv2_context *ctx,
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union mschapv2_password_hash *phash ) {
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uint8_t *dst;
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uint8_t *src;
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unsigned int i;
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/* Expand password hash by inserting (unused) DES parity bits */
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for ( i = ( sizeof ( phash->expand ) - 1 ) ; i > 0 ; i-- ) {
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dst = &phash->expand[i];
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src = ( dst - ( i / 8 ) );
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*dst = ( ( ( src[-1] << 8 ) | src[0] ) >> ( i % 8 ) );
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}
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DBGC ( ctx, "MSCHAPv2 expanded password hash:\n" );
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DBGC_HDA ( ctx, 0, phash->expand, sizeof ( phash->expand ) );
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}
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/**
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* Calculate MS-CHAPv2 challenge response
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*
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* @v ctx Context block
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* @v chash Challenge hash
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* @v phash Password hash (after expansion)
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* @v nt NT response to fill in
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*
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* This is the ChallengeResponse() function as documented in RFC 2759
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* section 8.5.
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*/
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static void
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mschapv2_challenge_response ( union mschapv2_context *ctx,
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const union mschapv2_challenge_hash *chash,
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const union mschapv2_password_hash *phash,
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struct mschapv2_nt_response *nt ) {
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struct cipher_algorithm *des = &des_algorithm;
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unsigned int i;
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int rc;
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/* Construct response. The design of the algorithm here is
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* interesting, suggesting that an intern at Microsoft had
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* heard the phrase "Triple DES" and hazarded a blind guess at
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* what it might mean.
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*/
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for ( i = 0 ; i < ( sizeof ( phash->des ) /
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sizeof ( phash->des[0] ) ) ; i++ ) {
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rc = cipher_setkey ( des, ctx->des, phash->des[i],
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sizeof ( phash->des[i] ) );
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assert ( rc == 0 ); /* no failure mode exists */
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cipher_encrypt ( des, ctx->des, chash->des, nt->block[i],
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sizeof ( chash->des ) );
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}
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DBGC ( ctx, "MSCHAPv2 NT response:\n" );
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DBGC_HDA ( ctx, 0, nt, sizeof ( *nt ) );
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}
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/**
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* Calculate MS-CHAPv2 challenge response
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*
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* @v username User name (or NULL to use empty string)
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* @v password Password (or NULL to use empty string)
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* @v challenge Authenticator challenge
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* @v peer Peer challenge
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* @v response Challenge response to fill in
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*
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* This is essentially the GenerateNTResponse() function as documented
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* in RFC 2759 section 8.1.
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*/
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void mschapv2_response ( const char *username, const char *password,
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const struct mschapv2_challenge *challenge,
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const struct mschapv2_challenge *peer,
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struct mschapv2_response *response ) {
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union mschapv2_context ctx;
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union mschapv2_challenge_hash chash;
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union mschapv2_password_hash phash;
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/* Zero reserved fields */
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memset ( response, 0, sizeof ( *response ) );
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/* Copy peer challenge to response */
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memcpy ( &response->peer, peer, sizeof ( response->peer ) );
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/* Construct challenge hash */
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mschapv2_challenge_hash ( &ctx, challenge, peer, username, &chash );
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/* Construct expanded password hash */
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mschapv2_password_hash ( &ctx, password, &phash );
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mschapv2_expand_hash ( &ctx, &phash );
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/* Construct NT response */
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mschapv2_challenge_response ( &ctx, &chash, &phash, &response->nt );
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DBGC ( &ctx, "MSCHAPv2 challenge response:\n" );
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DBGC_HDA ( &ctx, 0, response, sizeof ( *response ) );
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}
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/**
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* Calculate MS-CHAPv2 authenticator response
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*
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* @v username User name (or NULL to use empty string)
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* @v password Password (or NULL to use empty string)
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* @v challenge Authenticator challenge
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* @v response Challenge response
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* @v auth Authenticator response to fill in
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*
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* This is essentially the GenerateAuthenticatorResponse() function as
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* documented in RFC 2759 section 8.7.
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*/
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void mschapv2_auth ( const char *username, const char *password,
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const struct mschapv2_challenge *challenge,
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const struct mschapv2_response *response,
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struct mschapv2_auth *auth ) {
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struct digest_algorithm *sha1 = &sha1_algorithm;
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union mschapv2_context ctx;
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union mschapv2_challenge_hash chash;
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union mschapv2_password_hash phash;
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char tmp[3];
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char *wtf;
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unsigned int i;
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/* Construct hash of password hash */
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mschapv2_password_hash ( &ctx, password, &phash );
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mschapv2_hash_hash ( &ctx, &phash );
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/* Construct unnamed intermediate hash */
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digest_init ( sha1, ctx.sha1 );
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digest_update ( sha1, ctx.sha1, phash.md4, sizeof ( phash.md4 ) );
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digest_update ( sha1, ctx.sha1, &response->nt,
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sizeof ( response->nt ) );
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digest_update ( sha1, ctx.sha1, mschapv2_magic1,
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sizeof ( mschapv2_magic1 ) );
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digest_final ( sha1, ctx.sha1, phash.sha1 );
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DBGC ( &ctx, "MSCHAPv2 NT response:\n" );
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DBGC_HDA ( &ctx, 0, &response->nt, sizeof ( response->nt ) );
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DBGC ( &ctx, "MSCHAPv2 unnamed intermediate hash:\n" );
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DBGC_HDA ( &ctx, 0, phash.sha1, sizeof ( phash.sha1 ) );
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/* Construct challenge hash */
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mschapv2_challenge_hash ( &ctx, challenge, &response->peer,
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username, &chash );
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/* Construct authenticator response hash */
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digest_init ( sha1, ctx.sha1 );
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digest_update ( sha1, ctx.sha1, phash.sha1, sizeof ( phash.sha1 ) );
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digest_update ( sha1, ctx.sha1, chash.des, sizeof ( chash.des ) );
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digest_update ( sha1, ctx.sha1, mschapv2_magic2,
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sizeof ( mschapv2_magic2 ) );
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digest_final ( sha1, ctx.sha1, phash.sha1 );
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DBGC ( &ctx, "MSCHAPv2 authenticator response hash:\n" );
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DBGC_HDA ( &ctx, 0, phash.sha1, sizeof ( phash.sha1 ) );
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/* Encode authenticator response hash */
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wtf = auth->wtf;
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*(wtf++) = 'S';
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*(wtf++) = '=';
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DBGC ( &ctx, "MSCHAPv2 authenticator response: S=" );
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for ( i = 0 ; i < sizeof ( phash.sha1 ) ; i++ ) {
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snprintf ( tmp, sizeof ( tmp ), "%02X", phash.sha1[i] );
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*(wtf++) = tmp[0];
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*(wtf++) = tmp[1];
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DBGC ( &ctx, "%s", tmp );
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}
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DBGC ( &ctx, "\n" );
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}
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