/* $OpenBSD: mac.c,v 1.37 2025/09/05 10:01:35 dtucker Exp $ */

/*

 * Copyright (c) 2001 Markus Friedl.  All rights reserved.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * are met:

 * 1. Redistributions of source code must retain the above copyright

 *    notice, this list of conditions and the following disclaimer.

 * 2. Redistributions in binary form must reproduce the above copyright

 *    notice, this list of conditions and the following disclaimer in the

 *    documentation and/or other materials provided with the distribution.

 *

 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR

 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES

 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.

 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,

 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT

 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,

 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY

 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF

 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

 */

#include "includes.h"

#include <sys/types.h>

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include "digest.h"

#include "hmac.h"

#include "umac.h"

#include "mac.h"

#include "misc.h"

#include "ssherr.h"

#include "sshbuf.h"

#include "openbsd-compat/openssl-compat.h"

#define SSH_DIGEST  1  /* SSH_DIGEST_XXX */

#define SSH_UMAC  2  /* UMAC (not integrated with OpenSSL) */

#define SSH_UMAC128 3

struct macalg {

  char    *name;

  int   type;

  int   alg;

  int   truncatebits; /* truncate digest if != 0 */

  int   key_len;  /* just for UMAC */

  int   len;    /* just for UMAC */

  int   etm;    /* Encrypt-then-MAC */

};

static const struct macalg macs[] = {

  /* Encrypt-and-MAC (encrypt-and-authenticate) variants */

  { "hmac-sha1",        SSH_DIGEST, SSH_DIGEST_SHA1, 0, 0, 0, 0 },

  { "hmac-sha1-96",     SSH_DIGEST, SSH_DIGEST_SHA1, 96, 0, 0, 0 },

  { "hmac-sha2-256",      SSH_DIGEST, SSH_DIGEST_SHA256, 0, 0, 0, 0 },

  { "hmac-sha2-512",      SSH_DIGEST, SSH_DIGEST_SHA512, 0, 0, 0, 0 },

  { "hmac-md5",       SSH_DIGEST, SSH_DIGEST_MD5, 0, 0, 0, 0 },

  { "hmac-md5-96",      SSH_DIGEST, SSH_DIGEST_MD5, 96, 0, 0, 0 },

  { "none",                               SSH_DIGEST, SSH_DIGEST_NULL, 0, 0, 0, 0 },

  { "umac-64@openssh.com",    SSH_UMAC, 0, 0, 128, 64, 0 },

  { "umac-128@openssh.com",   SSH_UMAC128, 0, 0, 128, 128, 0 },

  /* Encrypt-then-MAC variants */

  { "hmac-sha1-etm@openssh.com",    SSH_DIGEST, SSH_DIGEST_SHA1, 0, 0, 0, 1 },

  { "hmac-sha1-96-etm@openssh.com", SSH_DIGEST, SSH_DIGEST_SHA1, 96, 0, 0, 1 },

  { "hmac-sha2-256-etm@openssh.com",  SSH_DIGEST, SSH_DIGEST_SHA256, 0, 0, 0, 1 },

  { "hmac-sha2-512-etm@openssh.com",  SSH_DIGEST, SSH_DIGEST_SHA512, 0, 0, 0, 1 },

  { "hmac-md5-etm@openssh.com",   SSH_DIGEST, SSH_DIGEST_MD5, 0, 0, 0, 1 },

  { "hmac-md5-96-etm@openssh.com",  SSH_DIGEST, SSH_DIGEST_MD5, 96, 0, 0, 1 },

  { "umac-64-etm@openssh.com",    SSH_UMAC, 0, 0, 128, 64, 1 },

  { "umac-128-etm@openssh.com",   SSH_UMAC128, 0, 0, 128, 128, 1 },

  { NULL,         0, 0, 0, 0, 0, 0 }

};

/* Returns a list of supported MACs separated by the specified char. */

char *

mac_alg_list(char sep)

{

  char *ret = NULL;

  const struct macalg *m;

  char sep_str[2] = {sep, '\0'};

  for (m = macs; m->name != NULL; m++)

    xextendf(&ret, sep_str, "%s", m->name);

  return ret;

}

static int

mac_setup_by_alg(struct sshmac *mac, const struct macalg *macalg)

{

  mac->type = macalg->type;

  if (mac->type == SSH_DIGEST) {

    if ((mac->hmac_ctx = ssh_hmac_start(macalg->alg)) == NULL)

      return SSH_ERR_ALLOC_FAIL;

    mac->key_len = mac->mac_len = ssh_hmac_bytes(macalg->alg);

  } else {

    mac->mac_len = macalg->len / 8;

    mac->key_len = macalg->key_len / 8;

    mac->umac_ctx = NULL;

  }

  if (macalg->truncatebits != 0)

    mac->mac_len = macalg->truncatebits / 8;

  mac->etm = macalg->etm;

  return 0;

}

int

mac_setup(struct sshmac *mac, char *name)

{

  const struct macalg *m;

  for (m = macs; m->name != NULL; m++) {

    if (strcmp(name, m->name) != 0)

      continue;

    if (mac != NULL)

      return mac_setup_by_alg(mac, m);

    return 0;

  }

  return SSH_ERR_INVALID_ARGUMENT;

}

int

mac_init(struct sshmac *mac)

{

  if (mac->key == NULL)

    return SSH_ERR_INVALID_ARGUMENT;

  switch (mac->type) {

  case SSH_DIGEST:

    if (mac->hmac_ctx == NULL ||

        ssh_hmac_init(mac->hmac_ctx, mac->key, mac->key_len) < 0)

      return SSH_ERR_INVALID_ARGUMENT;

    return 0;

  case SSH_UMAC:

    if ((mac->umac_ctx = umac_new(mac->key)) == NULL)

      return SSH_ERR_ALLOC_FAIL;

    return 0;

  case SSH_UMAC128:

    if ((mac->umac_ctx = umac128_new(mac->key)) == NULL)

      return SSH_ERR_ALLOC_FAIL;

    return 0;

  default:

    return SSH_ERR_INVALID_ARGUMENT;

  }

}

int

mac_compute(struct sshmac *mac, u_int32_t seqno,

    const u_char *data, int datalen,

    u_char *digest, size_t dlen)

{

  static union {

    u_char m[SSH_DIGEST_MAX_LENGTH];

    u_int64_t for_align;

  } u;

  u_char b[4];

  u_char nonce[8];

  if (mac->mac_len > sizeof(u))

    return SSH_ERR_INTERNAL_ERROR;

  switch (mac->type) {

  case SSH_DIGEST:

    put_u32(b, seqno);

    /* reset HMAC context */

    if (ssh_hmac_init(mac->hmac_ctx, NULL, 0) < 0 ||

        ssh_hmac_update(mac->hmac_ctx, b, sizeof(b)) < 0 ||

        ssh_hmac_update(mac->hmac_ctx, data, datalen) < 0 ||

        ssh_hmac_final(mac->hmac_ctx, u.m, sizeof(u.m)) < 0)

      return SSH_ERR_LIBCRYPTO_ERROR;

    break;

  case SSH_UMAC:

    POKE_U64(nonce, seqno);

    umac_update(mac->umac_ctx, data, datalen);

    umac_final(mac->umac_ctx, u.m, nonce);

    break;

  case SSH_UMAC128:

    put_u64(nonce, seqno);

    umac128_update(mac->umac_ctx, data, datalen);

    umac128_final(mac->umac_ctx, u.m, nonce);

    break;

  default:

    return SSH_ERR_INVALID_ARGUMENT;

  }

  if (digest != NULL) {

    if (dlen > mac->mac_len)

      dlen = mac->mac_len;

    memcpy(digest, u.m, dlen);

  }

  return 0;

}

int

mac_check(struct sshmac *mac, u_int32_t seqno,

    const u_char *data, size_t dlen,

    const u_char *theirmac, size_t mlen)

{

  u_char ourmac[SSH_DIGEST_MAX_LENGTH];

  int r;

  if (mac->mac_len > mlen)

    return SSH_ERR_INVALID_ARGUMENT;

  if ((r = mac_compute(mac, seqno, data, dlen,

      ourmac, sizeof(ourmac))) != 0)

    return r;

  if (timingsafe_bcmp(ourmac, theirmac, mac->mac_len) != 0)

    return SSH_ERR_MAC_INVALID;

  return 0;

}

void

mac_clear(struct sshmac *mac)

{

  if (mac->type == SSH_UMAC) {

    if (mac->umac_ctx != NULL)

      umac_delete(mac->umac_ctx);

  } else if (mac->type == SSH_UMAC128) {

    if (mac->umac_ctx != NULL)

      umac128_delete(mac->umac_ctx);

  } else if (mac->hmac_ctx != NULL)

    ssh_hmac_free(mac->hmac_ctx);

  mac->hmac_ctx = NULL;

  mac->umac_ctx = NULL;

}

/* XXX copied from ciphers_valid */

#define MAC_SEP ","

int

mac_valid(const char *names)

{

  char *maclist, *cp, *p;

  if (names == NULL || strcmp(names, "") == 0)

    return 0;

  if ((maclist = cp = strdup(names)) == NULL)

    return 0;

  for ((p = strsep(&cp, MAC_SEP)); p && *p != '\0';

      (p = strsep(&cp, MAC_SEP))) {

    if (mac_setup(NULL, p) < 0) {

      free(maclist);

      return 0;

    }

  }

  free(maclist);

  return 1;

}