/*
* Copyright (C) 2024 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., 51 Franklin Street, Fifth Floor, Boston, MA
* 02110-1301, USA.
*
* You can also choose to distribute this program under the terms of
* the Unmodified Binary Distribution Licence (as given in the file
* COPYING.UBDL), provided that you have satisfied its requirements.
*/
FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
/** @file
*
* MS-CHAPv2 authentication
*
* The algorithms used for MS-CHAPv2 authentication are defined in
* RFC 2759 section 8.
*/
#include <stdio.h>
#include <string.h>
#include <byteswap.h>
#include <ipxe/md4.h>
#include <ipxe/sha1.h>
#include <ipxe/des.h>
#include <ipxe/mschapv2.h>
/**
* MS-CHAPv2 context block
*
* For no particularly discernible reason, MS-CHAPv2 uses two
* different digest algorithms and one block cipher. The uses do not
* overlap, so share the context storage between these to reduce stack
* usage.
*/
union mschapv2_context {
/** SHA-1 digest context */
uint8_t sha1[SHA1_CTX_SIZE];
/** MD4 digest context */
uint8_t md4[MD4_CTX_SIZE];
/** DES cipher context */
uint8_t des[DES_CTX_SIZE];
};
/**
* MS-CHAPv2 challenge hash
*
* MS-CHAPv2 calculates the SHA-1 digest of the peer challenge, the
* authenticator challenge, and the username, and then uses only the
* first 8 bytes of the result (as a DES plaintext block).
*/
union mschapv2_challenge_hash {
/** SHA-1 digest */
uint8_t sha1[SHA1_DIGEST_SIZE];
/** DES plaintext block */
uint8_t des[DES_BLOCKSIZE];
};
/**
* MS-CHAPv2 password hash
*
* MS-CHAPv2 calculates the MD4 digest of an unspecified two-byte
* little-endian Unicode encoding (presumably either UCS-2LE or
* UTF-16LE) of the password.
*
* For constructing the challenge response, the MD4 digest is then
* zero-padded to 21 bytes and used as three separate 56-bit DES keys.
*
* For constructing the authenticator response, the MD4 digest is then
* used as an input to a SHA-1 digest along with the NT response and a
* magic constant.
*/
union mschapv2_password_hash {
/** MD4 digest */
uint8_t md4[MD4_DIGEST_SIZE];
/** SHA-1 digest */
uint8_t sha1[SHA1_DIGEST_SIZE];
/** DES keys */
uint8_t des[3][DES_BLOCKSIZE];
/** DES key expansion */
uint8_t expand[ 3 * DES_BLOCKSIZE ];
};
/** MS-CHAPv2 magic constant 1 */
static const char mschapv2_magic1[39] =
"Magic server to client signing constant";
/** MS-CHAPv2 magic constant 2 */
static const char mschapv2_magic2[41] =
"Pad to make it do more than one iteration";
/**
* Calculate MS-CHAPv2 challenge hash
*
* @v ctx Context block
* @v challenge Authenticator challenge
* @v peer Peer challenge
* @v username User name (or NULL to use empty string)
* @v chash Challenge hash to fill in
*
* This is the ChallengeHash() function as documented in RFC 2759
* section 8.2.
*/
static void
mschapv2_challenge_hash ( union mschapv2_context *ctx,
const struct mschapv2_challenge *challenge,
const struct mschapv2_challenge *peer,
const char *username,
union mschapv2_challenge_hash *chash ) {
struct digest_algorithm *sha1 = &sha1_algorithm;
/* Calculate SHA-1 hash of challenges and username */
digest_init ( sha1, ctx->sha1 );
digest_update ( sha1, ctx->sha1, peer, sizeof ( *peer ) );
digest_update ( sha1, ctx->sha1, challenge, sizeof ( *challenge ) );
if ( username ) {
digest_update ( sha1, ctx->sha1, username,
strlen ( username ) );
}
digest_final ( sha1, ctx->sha1, chash->sha1 );
DBGC ( ctx, "MSCHAPv2 authenticator challenge:\n" );
DBGC_HDA ( ctx, 0, challenge, sizeof ( *challenge ) );
DBGC ( ctx, "MSCHAPv2 peer challenge:\n" );
DBGC_HDA ( ctx, 0, peer, sizeof ( *peer ) );
DBGC ( ctx, "MSCHAPv2 challenge hash:\n" );
DBGC_HDA ( ctx, 0, chash->des, sizeof ( chash->des ) );
}
/**
* Calculate MS-CHAPv2 password hash
*
* @v ctx Context block
* @v password Password (or NULL to use empty string)
* @v phash Password hash to fill in
*
* This is the NtPasswordHash() function as documented in RFC 2759
* section 8.3.
*/
static void mschapv2_password_hash ( union mschapv2_context *ctx,
const char *password,
union mschapv2_password_hash *phash ) {
struct digest_algorithm *md4 = &md4_algorithm;
uint16_t wc;
uint8_t c;
/* Construct zero-padded MD4 hash of encoded password */
memset ( phash, 0, sizeof ( *phash ) );
digest_init ( md4, ctx->md4 );
if ( password ) {
while ( ( c = *(password++) ) ) {
wc = cpu_to_le16 ( c );
digest_update ( md4, ctx->md4, &wc, sizeof ( wc ) );
}
}
digest_final ( md4, ctx->md4, phash->md4 );
DBGC ( ctx, "MSCHAPv2 password hash:\n" );
DBGC_HDA ( ctx, 0, phash->md4, sizeof ( phash->md4 ) );
}
/**
* Hash the MS-CHAPv2 password hash
*
* @v ctx Context block
* @v phash Password hash to be rehashed
*
* This is the HashNtPasswordHash() function as documented in RFC 2759
* section 8.4.
*/
static void mschapv2_hash_hash ( union mschapv2_context *ctx,
union mschapv2_password_hash *phash ) {
struct digest_algorithm *md4 = &md4_algorithm;
/* Calculate MD4 hash of existing MD4 hash */
digest_init ( md4, ctx->md4 );
digest_update ( md4, ctx->md4, phash->md4, sizeof ( phash->md4 ) );
digest_final ( md4, ctx->md4, phash->md4 );
DBGC ( ctx, "MSCHAPv2 password hash hash:\n" );
DBGC_HDA ( ctx, 0, phash->md4, sizeof ( phash->md4 ) );
}
/**
* Expand MS-CHAPv2 password hash by inserting DES dummy parity bits
*
* @v ctx Context block
* @v phash Password hash to expand
*
* This is part of the DesEncrypt() function as documented in RFC 2759
* section 8.6.
*/
static void mschapv2_expand_hash ( union mschapv2_context *ctx,
union mschapv2_password_hash *phash ) {
uint8_t *dst;
uint8_t *src;
unsigned int i;
/* Expand password hash by inserting (unused) DES parity bits */
for ( i = ( sizeof ( phash->expand ) - 1 ) ; i > 0 ; i-- ) {
dst = &phash->expand[i];
src = ( dst - ( i / 8 ) );
*dst = ( ( ( src[-1] << 8 ) | src[0] ) >> ( i % 8 ) );
}
DBGC ( ctx, "MSCHAPv2 expanded password hash:\n" );
DBGC_HDA ( ctx, 0, phash->expand, sizeof ( phash->expand ) );
}
/**
* Calculate MS-CHAPv2 challenge response
*
* @v ctx Context block
* @v chash Challenge hash
* @v phash Password hash (after expansion)
* @v nt NT response to fill in
*
* This is the ChallengeResponse() function as documented in RFC 2759
* section 8.5.
*/
static void
mschapv2_challenge_response ( union mschapv2_context *ctx,
const union mschapv2_challenge_hash *chash,
const union mschapv2_password_hash *phash,
struct mschapv2_nt_response *nt ) {
struct cipher_algorithm *des = &des_algorithm;
unsigned int i;
int rc;
/* Construct response. The design of the algorithm here is
* interesting, suggesting that an intern at Microsoft had
* heard the phrase "Triple DES" and hazarded a blind guess at
* what it might mean.
*/
for ( i = 0 ; i < ( sizeof ( phash->des ) /
sizeof ( phash->des[0] ) ) ; i++ ) {
rc = cipher_setkey ( des, ctx->des, phash->des[i],
sizeof ( phash->des[i] ) );
assert ( rc == 0 ); /* no failure mode exists */
cipher_encrypt ( des, ctx->des, chash->des, nt->block[i],
sizeof ( chash->des ) );
}
DBGC ( ctx, "MSCHAPv2 NT response:\n" );
DBGC_HDA ( ctx, 0, nt, sizeof ( *nt ) );
}
/**
* Calculate MS-CHAPv2 challenge response
*
* @v username User name (or NULL to use empty string)
* @v password Password (or NULL to use empty string)
* @v challenge Authenticator challenge
* @v peer Peer challenge
* @v response Challenge response to fill in
*
* This is essentially the GenerateNTResponse() function as documented
* in RFC 2759 section 8.1.
*/
void mschapv2_response ( const char *username, const char *password,
const struct mschapv2_challenge *challenge,
const struct mschapv2_challenge *peer,
struct mschapv2_response *response ) {
union mschapv2_context ctx;
union mschapv2_challenge_hash chash;
union mschapv2_password_hash phash;
/* Zero reserved fields */
memset ( response, 0, sizeof ( *response ) );
/* Copy peer challenge to response */
memcpy ( &response->peer, peer, sizeof ( response->peer ) );
/* Construct challenge hash */
mschapv2_challenge_hash ( &ctx, challenge, peer, username, &chash );
/* Construct expanded password hash */
mschapv2_password_hash ( &ctx, password, &phash );
mschapv2_expand_hash ( &ctx, &phash );
/* Construct NT response */
mschapv2_challenge_response ( &ctx, &chash, &phash, &response->nt );
DBGC ( &ctx, "MSCHAPv2 challenge response:\n" );
DBGC_HDA ( &ctx, 0, response, sizeof ( *response ) );
}
/**
* Calculate MS-CHAPv2 authenticator response
*
* @v username User name (or NULL to use empty string)
* @v password Password (or NULL to use empty string)
* @v challenge Authenticator challenge
* @v response Challenge response
* @v auth Authenticator response to fill in
*
* This is essentially the GenerateAuthenticatorResponse() function as
* documented in RFC 2759 section 8.7.
*/
void mschapv2_auth ( const char *username, const char *password,
const struct mschapv2_challenge *challenge,
const struct mschapv2_response *response,
struct mschapv2_auth *auth ) {
struct digest_algorithm *sha1 = &sha1_algorithm;
union mschapv2_context ctx;
union mschapv2_challenge_hash chash;
union mschapv2_password_hash phash;
char tmp[3];
char *wtf;
unsigned int i;
/* Construct hash of password hash */
mschapv2_password_hash ( &ctx, password, &phash );
mschapv2_hash_hash ( &ctx, &phash );
/* Construct unnamed intermediate hash */
digest_init ( sha1, ctx.sha1 );
digest_update ( sha1, ctx.sha1, phash.md4, sizeof ( phash.md4 ) );
digest_update ( sha1, ctx.sha1, &response->nt,
sizeof ( response->nt ) );
digest_update ( sha1, ctx.sha1, mschapv2_magic1,
sizeof ( mschapv2_magic1 ) );
digest_final ( sha1, ctx.sha1, phash.sha1 );
DBGC ( &ctx, "MSCHAPv2 NT response:\n" );
DBGC_HDA ( &ctx, 0, &response->nt, sizeof ( response->nt ) );
DBGC ( &ctx, "MSCHAPv2 unnamed intermediate hash:\n" );
DBGC_HDA ( &ctx, 0, phash.sha1, sizeof ( phash.sha1 ) );
/* Construct challenge hash */
mschapv2_challenge_hash ( &ctx, challenge, &response->peer,
username, &chash );
/* Construct authenticator response hash */
digest_init ( sha1, ctx.sha1 );
digest_update ( sha1, ctx.sha1, phash.sha1, sizeof ( phash.sha1 ) );
digest_update ( sha1, ctx.sha1, chash.des, sizeof ( chash.des ) );
digest_update ( sha1, ctx.sha1, mschapv2_magic2,
sizeof ( mschapv2_magic2 ) );
digest_final ( sha1, ctx.sha1, phash.sha1 );
DBGC ( &ctx, "MSCHAPv2 authenticator response hash:\n" );
DBGC_HDA ( &ctx, 0, phash.sha1, sizeof ( phash.sha1 ) );
/* Encode authenticator response hash */
wtf = auth->wtf;
*(wtf++) = 'S';
*(wtf++) = '=';
DBGC ( &ctx, "MSCHAPv2 authenticator response: S=" );
for ( i = 0 ; i < sizeof ( phash.sha1 ) ; i++ ) {
snprintf ( tmp, sizeof ( tmp ), "%02X", phash.sha1[i] );
*(wtf++) = tmp[0];
*(wtf++) = tmp[1];
DBGC ( &ctx, "%s", tmp );
}
DBGC ( &ctx, "\n" );
}
