/* $OpenBSD: cipher.c,v 1.125 2025/09/02 11:08:34 djm Exp $ */

/*

 * Author: Tatu Ylonen <ylo@cs.hut.fi>

 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland

 *                    All rights reserved

 *

 * As far as I am concerned, the code I have written for this software

 * can be used freely for any purpose.  Any derived versions of this

 * software must be clearly marked as such, and if the derived work is

 * incompatible with the protocol description in the RFC file, it must be

 * called by a name other than "ssh" or "Secure Shell".

 *

 *

 * Copyright (c) 1999 Niels Provos.  All rights reserved.

 * Copyright (c) 1999, 2000 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 <string.h>

#include <stdarg.h>

#include <stdio.h>

#include "cipher.h"

#include "misc.h"

#include "sshbuf.h"

#include "ssherr.h"

#include "digest.h"

#include "log.h"

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

/* for provider functions */

#ifdef WITH_OPENSSL3

#include <openssl/err.h>

#include <openssl/params.h>

#include <openssl/provider.h>

#endif

#ifndef WITH_OPENSSL

#define EVP_CIPHER_CTX void

#define EVP_CIPHER void

#else

/* for multi-threaded aes-ctr cipher */

extern const EVP_CIPHER *evp_aes_ctr_mt(void);

#endif

struct sshcipher_ctx {

  int plaintext;

  int encrypt;

  EVP_CIPHER_CTX *evp;

  const EVP_CIPHER *meth_ptr; /*used to free memory in aes_ctr_mt */

  struct chachapoly_ctx *cp_ctx;

#ifdef WITH_OPENSSL

  struct chachapoly_ctx_mt *cp_ctx_mt;

#endif

  struct aesctr_ctx ac_ctx; /* XXX union with evp? */

  const struct sshcipher *cipher;

};

struct sshcipher {

  char  *name;

  u_int block_size;

  u_int key_len;

  u_int iv_len;   /* defaults to block_size */

  u_int auth_len;

  u_int flags;

#define CFLAG_CBC   (1<<0)

#define CFLAG_CHACHAPOLY  (1<<1)

#define CFLAG_AESCTR    (1<<2)

#define CFLAG_NONE    (1<<3)

#define CFLAG_INTERNAL 0

#ifdef WITH_OPENSSL

#define CFLAG_MT    (1<<4)

  const EVP_CIPHER  *(*evptype)(void);

#else

  void  *ignored;

#endif

};

static struct sshcipher ciphers[] = {

#ifdef WITH_OPENSSL

#ifndef OPENSSL_NO_DES

  { "3des-cbc",   8, 24, 0, 0, CFLAG_CBC, EVP_des_ede3_cbc },

#endif

  { "aes128-cbc",   16, 16, 0, 0, CFLAG_CBC, EVP_aes_128_cbc },

  { "aes192-cbc",   16, 24, 0, 0, CFLAG_CBC, EVP_aes_192_cbc },

  { "aes256-cbc",   16, 32, 0, 0, CFLAG_CBC, EVP_aes_256_cbc },

  { "aes128-ctr",   16, 16, 0, 0, 0, EVP_aes_128_ctr },

  { "aes192-ctr",   16, 24, 0, 0, 0, EVP_aes_192_ctr },

  { "aes256-ctr",   16, 32, 0, 0, 0, EVP_aes_256_ctr },

  { "aes128-gcm@openssh.com",

        16, 16, 12, 16, 0, EVP_aes_128_gcm },

  { "aes256-gcm@openssh.com",

        16, 32, 12, 16, 0, EVP_aes_256_gcm },

#else

  { "aes128-ctr",   16, 16, 0, 0, CFLAG_AESCTR, NULL },

  { "aes192-ctr",   16, 24, 0, 0, CFLAG_AESCTR, NULL },

  { "aes256-ctr",   16, 32, 0, 0, CFLAG_AESCTR, NULL },

#endif

  { "chacha20-poly1305@openssh.com",

        8, 64, 0, 16, CFLAG_CHACHAPOLY, NULL },

#ifdef WITH_OPENSSL

  { "chacha20-poly1305-mt@hpnssh.org",

        8, 64, 0, 16, CFLAG_CHACHAPOLY|CFLAG_MT, NULL },

#endif

  { "none",               8, 0, 0, 0, CFLAG_NONE, NULL },

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

};

/*--*/

/* Returns a comma-separated list of supported ciphers. */

char *

cipher_alg_list(char sep, int auth_only)

{

  char *ret = NULL;

  const struct sshcipher *c;

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

  for (c = ciphers; c->name != NULL; c++) {

    if ((c->flags & CFLAG_INTERNAL) != 0)

      continue;

    if (auth_only && c->auth_len == 0)

      continue;

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

  }

  return ret;

}

const char *

compression_alg_list(int compression)

{

#ifdef WITH_ZLIB

  return compression ? "zlib@openssh.com,none" :

      "none,zlib@openssh.com";

#else

  return "none";

#endif

}

/* used to get the cipher name when we are testing to

 * see if we can move from a serial to parallel cipher

 * only called in cipher-switch.c

 */

const char *

cipher_ctx_name(const struct sshcipher_ctx *cc)

{

        return cc->cipher->name;

}

u_int

cipher_blocksize(const struct sshcipher *c)

{

  return (c->block_size);

}

uint64_t

cipher_rekey_blocks(const struct sshcipher *c)

{

  /*

   * Chacha20-Poly1305 does not benefit from data-based rekeying,

   * per "The Security of ChaCha20-Poly1305 in the Multi-user Setting",

   * Degabriele, J. P., Govinden, J, Gunther, F. and Paterson K.

   * ACM CCS 2021; https://eprint.iacr.org/2023/085.pdf

   *

   * Cryptanalysis aside, we do still want do need to prevent the SSH

   * sequence number wrapping and also to rekey to provide some

   * protection for long lived sessions against key disclosure at the

   * endpoints, so arrange for rekeying every 2**32 blocks as the

   * 128-bit block ciphers do (i.e. every 32GB data).

   */

  if ((c->flags & CFLAG_CHACHAPOLY) != 0)

    return (uint64_t)1 << 32;

  /* there is no actual need to rekey the NULL cipher but

   * rekeying is a necessary step. In part, as mentioned above,

   * to keep the seqnr from wrapping. So we set it to the

   * maximum possible -cjr 4/10/23 */

  if ((c->flags & CFLAG_NONE) != 0)

    return (uint64_t)1 << 32;

  /*

   * The 2^(blocksize*2) limit is too expensive for 3DES,

   * so enforce a 1GB data limit for small blocksizes.

   * See discussion in RFC4344 section 3.2.

   */

  if (c->block_size < 16)

    return ((uint64_t)1 << 30) / c->block_size;

  /*

   * Otherwise, use the RFC4344 s3.2 recommendation of 2**(L/4) blocks

   * before rekeying where L is the blocksize in bits.

   * Most other ciphers have a 128 bit blocksize, so this equates to

   * 2**32 blocks / 64GB data.

   */

  return (uint64_t)1 << (c->block_size * 2);

}

u_int

cipher_keylen(const struct sshcipher *c)

{

  return (c->key_len);

}

u_int

cipher_seclen(const struct sshcipher *c)

{

  if (strcmp("3des-cbc", c->name) == 0)

    return 14;

  return cipher_keylen(c);

}

u_int

cipher_authlen(const struct sshcipher *c)

{

  return (c->auth_len);

}

u_int

cipher_ivlen(const struct sshcipher *c)

{

  /*

   * Default is cipher block size, except for chacha20+poly1305 that

   * needs no IV. XXX make iv_len == -1 default?

   */

  return (c->iv_len != 0 || (c->flags & CFLAG_CHACHAPOLY) != 0) ?

      c->iv_len : c->block_size;

}

u_int

cipher_is_cbc(const struct sshcipher *c)

{

  return (c->flags & CFLAG_CBC) != 0;

}

u_int

cipher_ctx_is_plaintext(struct sshcipher_ctx *cc)

{

  return cc->plaintext;

}

struct sshcipher *

cipher_by_name(const char *name)

{

  struct sshcipher *c;

  for (c = ciphers; c->name != NULL; c++)

    if (strcmp(c->name, name) == 0)

      return c;

  return NULL;

}

#define CIPHER_SEP  ","

int

ciphers_valid(const char *names)

{

  const struct sshcipher *c;

  char *cipher_list, *cp;

  char *p;

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

    return 0;

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

    return 0;

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

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

    c = cipher_by_name(p);

      if (c == NULL || ((c->flags & CFLAG_INTERNAL) != 0 &&

            (c->flags & CFLAG_NONE) != 0)) {

      free(cipher_list);

      return 0;

    }

  }

  free(cipher_list);

  return 1;

}

const char *

cipher_warning_message(const struct sshcipher_ctx *cc)

{

  if (cc == NULL || cc->cipher == NULL)

    return NULL;

  /* XXX repurpose for CBC warning */

  return NULL;

}

int

cipher_init(struct sshcipher_ctx **ccp, const struct sshcipher *cipher,

    const u_char *key, u_int keylen, const u_char *iv, u_int ivlen,

    u_int seqnr, int do_encrypt, int enable_threads)

{

  struct sshcipher_ctx *cc = NULL;

  int ret = SSH_ERR_INTERNAL_ERROR;

#ifdef WITH_OPENSSL

  const EVP_CIPHER *type;

  int klen;

#endif

  *ccp = NULL;

  if ((cc = calloc(1, sizeof(*cc))) == NULL)

    return SSH_ERR_ALLOC_FAIL;

  cc->plaintext = (cipher->flags & CFLAG_NONE) != 0;

  cc->encrypt = do_encrypt;

  cc->meth_ptr = NULL;

  if (keylen < cipher->key_len ||

      (iv != NULL && ivlen < cipher_ivlen(cipher))) {

    ret = SSH_ERR_INVALID_ARGUMENT;

    goto out;

  }

  cc->cipher = cipher;

  if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {

#ifdef WITH_OPENSSL

    if ((cc->cipher->flags & CFLAG_MT) != 0) {

      cc->cp_ctx_mt = chachapoly_new_mt(seqnr, key, keylen);

      ret = cc->cp_ctx_mt != NULL ? 0 :

          SSH_ERR_INVALID_ARGUMENT;

    } else {

      cc->cp_ctx = chachapoly_new(key, keylen);

      ret = cc->cp_ctx != NULL ? 0 : SSH_ERR_INVALID_ARGUMENT;

    }

#else

    cc->cp_ctx = chachapoly_new(key, keylen);

    ret = cc->cp_ctx != NULL ? 0 : SSH_ERR_INVALID_ARGUMENT;

#endif

    goto out;

  }

  if ((cc->cipher->flags & CFLAG_NONE) != 0) {

    ret = 0;

    goto out;

  }

#ifndef WITH_OPENSSL

  if ((cc->cipher->flags & CFLAG_AESCTR) != 0) {

    aesctr_keysetup(&cc->ac_ctx, key, 8 * keylen, 8 * ivlen);

    aesctr_ivsetup(&cc->ac_ctx, iv);

    ret = 0;

    goto out;

  }

  ret = SSH_ERR_INVALID_ARGUMENT;

  goto out;

#else /* WITH_OPENSSL */

  type = (*cipher->evptype)();

  if ((cc->evp = EVP_CIPHER_CTX_new()) == NULL) {

    ret = SSH_ERR_ALLOC_FAIL;

    goto out;

  }

  /* the following block is for AES-CTR-MT cipher switching

   * if we are using the ctr cipher and we are post-auth then

   * start the threaded cipher. If OSSL supports providers (OSSL 3.0+) then

   * we load our hpnssh provider. If it doesn't (OSSL < 1.1) then we use the

   * _meth_new process found in cipher-ctr-mt.c */

  if (strstr(cc->cipher->name, "ctr") && enable_threads) {

#ifdef WITH_OPENSSL3

    /* this version of openssl uses providers */

    OSSL_LIB_CTX *aes_lib = NULL; /* probably not needed */

    OSSL_PROVIDER *aes_mt_provider = NULL;

    type = NULL;

    if (OSSL_PROVIDER_add_builtin(aes_lib, "hpnssh",

                OSSL_provider_init) != 1) {

      fatal("Failed to add HPNSSH provider for AES-CTR");

    }

    aes_mt_provider = OSSL_PROVIDER_load(aes_lib, "hpnssh");

    if (aes_mt_provider != NULL) {

      /* use the previous key length to determine which cipher to load */

      if (cipher->key_len == 32)

        type = EVP_CIPHER_fetch(aes_lib, "aes_ctr_mt_256", NULL);

      if (cipher->key_len == 24)

        type = EVP_CIPHER_fetch(aes_lib, "aes_ctr_mt_192", NULL);

      if (cipher->key_len == 16)

        type = EVP_CIPHER_fetch(aes_lib, "aes_ctr_mt_128", NULL);

      if (type == NULL) {

        ERR_print_errors_fp(stderr);

        fatal("FAILED TO LOAD aes_ctr_mt");

      } else {

        debug("LOADED aes_ctr_mt");

      }

    }

    else {

      ERR_print_errors_fp(stderr);

      fatal("Failed to load HPN-SSH AES-CTR-MT provider.");

    }

#else

    type = (*evp_aes_ctr_mt)(); /* see cipher-ctr-mt.c */

    /* we need to free this later if using aes_ctr_mt

     * under OSSL 1.1. Honestly, we could avoid this by making

     * it a global in cipher-ctr_mt.c and exporting it here

     * then we'd only have to call EVP_CIPHER_meth once but this

     * works for now. TODO: This. cjr 02.22.2023 */

    cc->meth_ptr = type;

#endif /* WITH_OPENSSL3 */

  } /* if (strstr()) */

  if (EVP_CipherInit(cc->evp, type, NULL, (u_char *)iv,

      (do_encrypt == CIPHER_ENCRYPT)) == 0) {

    ret = SSH_ERR_LIBCRYPTO_ERROR;

    goto out;

  }

  if (cipher_authlen(cipher) &&

      EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_SET_IV_FIXED,

      -1, (u_char *)iv) <= 0) {

    ret = SSH_ERR_LIBCRYPTO_ERROR;

    goto out;

  }

  klen = EVP_CIPHER_CTX_key_length(cc->evp);

  if (klen > 0 && keylen != (u_int)klen) {

    if (EVP_CIPHER_CTX_set_key_length(cc->evp, keylen) == 0) {

      ret = SSH_ERR_LIBCRYPTO_ERROR;

      goto out;

    }

  }

  if (EVP_CipherInit(cc->evp, NULL, (u_char *)key, NULL, -1) == 0) {

    ret = SSH_ERR_LIBCRYPTO_ERROR;

    goto out;

  }

  ret = 0;

#endif /* WITH_OPENSSL */

 out:

  if (ret == 0) {

    /* success */

    *ccp = cc;

  } else {

    if (cc != NULL) {

#ifdef WITH_OPENSSL

      EVP_CIPHER_CTX_free(cc->evp);

#endif /* WITH_OPENSSL */

      freezero(cc, sizeof(*cc));

    }

  }

  return ret;

}

/*

 * cipher_crypt() operates as following:

 * Copy 'aadlen' bytes (without en/decryption) from 'src' to 'dest'.

 * These bytes are treated as additional authenticated data for

 * authenticated encryption modes.

 * En/Decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'.

 * Use 'authlen' bytes at offset 'len'+'aadlen' as the authentication tag.

 * This tag is written on encryption and verified on decryption.

 * Both 'aadlen' and 'authlen' can be set to 0.

 */

int

cipher_crypt(struct sshcipher_ctx *cc, u_int seqnr, u_char *dest,

   const u_char *src, u_int len, u_int aadlen, u_int authlen)

{

  if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {

#ifdef WITH_OPENSSL

    if ((cc->cipher->flags & CFLAG_MT) != 0) {

      return chachapoly_crypt_mt(cc->cp_ctx_mt, seqnr, dest,

          src, len, aadlen, authlen, cc->encrypt);

    }

#endif

    return chachapoly_crypt(cc->cp_ctx, seqnr, dest, src,

        len, aadlen, authlen, cc->encrypt);

  }

  if ((cc->cipher->flags & CFLAG_NONE) != 0) {

    memcpy(dest, src, aadlen + len);

    return 0;

  }

#ifndef WITH_OPENSSL

  if ((cc->cipher->flags & CFLAG_AESCTR) != 0) {

    if (aadlen)

      memcpy(dest, src, aadlen);

    aesctr_encrypt_bytes(&cc->ac_ctx, src + aadlen, dest + aadlen,

        len);

    return 0;

  }

  return SSH_ERR_INVALID_ARGUMENT;

#else

  if (authlen) {

    u_char lastiv[1];

    if (authlen != cipher_authlen(cc->cipher))

      return SSH_ERR_INVALID_ARGUMENT;

    /* increment IV */

    if (EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_IV_GEN,

        1, lastiv) <= 0)

      return SSH_ERR_LIBCRYPTO_ERROR;

    /* set tag on decryption */

    if (!cc->encrypt &&

        EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_SET_TAG,

        authlen, (u_char *)src + aadlen + len) <= 0)

      return SSH_ERR_LIBCRYPTO_ERROR;

  }

  if (aadlen) {

    if (authlen &&

        EVP_Cipher(cc->evp, NULL, (u_char *)src, aadlen) < 0)

      return SSH_ERR_LIBCRYPTO_ERROR;

    memcpy(dest, src, aadlen);

  }

  if (len % cc->cipher->block_size)

    return SSH_ERR_INVALID_ARGUMENT;

  if (EVP_Cipher(cc->evp, dest + aadlen, (u_char *)src + aadlen,

      len) < 0)

    return SSH_ERR_LIBCRYPTO_ERROR;

  if (authlen) {

    /* compute tag (on encrypt) or verify tag (on decrypt) */

    if (EVP_Cipher(cc->evp, NULL, NULL, 0) < 0)

      return cc->encrypt ?

          SSH_ERR_LIBCRYPTO_ERROR : SSH_ERR_MAC_INVALID;

    if (cc->encrypt &&

        EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_GET_TAG,

        authlen, dest + aadlen + len) <= 0)

      return SSH_ERR_LIBCRYPTO_ERROR;

  }

  return 0;

#endif

}

/* Extract the packet length, including any decryption necessary beforehand */

int

cipher_get_length(struct sshcipher_ctx *cc, u_int *plenp, u_int seqnr,

    const u_char *cp, u_int len)

{

  if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {

#ifdef WITH_OPENSSL

    if ((cc->cipher->flags & CFLAG_MT) != 0) {

      return chachapoly_get_length_mt(cc->cp_ctx_mt, plenp,

          seqnr, cp, len);

    }

#endif

    return chachapoly_get_length(cc->cp_ctx, plenp, seqnr,

        cp, len);

  }

  if (len < 4)

    return SSH_ERR_MESSAGE_INCOMPLETE;

  *plenp = PEEK_U32(cp);

  return 0;

}

void

cipher_free(struct sshcipher_ctx *cc)

{

  if (cc == NULL)

    return;

  if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {

#ifdef WITH_OPENSSL

    if ((cc->cipher->flags & CFLAG_MT) != 0) {

      chachapoly_free_mt(cc->cp_ctx_mt);

      cc->cp_ctx_mt = NULL;

    } else {

      chachapoly_free(cc->cp_ctx);

      cc->cp_ctx = NULL;

    }

#else

    chachapoly_free(cc->cp_ctx);

    cc->cp_ctx = NULL;

#endif

  } else if ((cc->cipher->flags & CFLAG_AESCTR) != 0)

    explicit_bzero(&cc->ac_ctx, sizeof(cc->ac_ctx));

#ifdef WITH_OPENSSL

  EVP_CIPHER_CTX_free(cc->evp);

  cc->evp = NULL;

  /* if meth_ptr isn't null then we are using the aes_ctr_mt

   * evp_cipher_meth_new() in cipher-ctr-mt.c under OSSL 1.1

   * if we don't explicitly free it then, even though we free

   * the ctx it is a part of it doesn't get freed. So...

   * cjr 2/7/2023

   */

  if (cc->meth_ptr != NULL) {

    EVP_CIPHER_meth_free((void *)(EVP_CIPHER *)cc->meth_ptr);

    cc->meth_ptr = NULL;

  }

#endif

  freezero(cc, sizeof(*cc));

}

int

cipher_get_keyiv(struct sshcipher_ctx *cc, u_char *iv, size_t len)

{

#ifdef WITH_OPENSSL

  const struct sshcipher *c = cc->cipher;

  int evplen;

#endif

  if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0) {

    if (len != 0)

      return SSH_ERR_INVALID_ARGUMENT;

    return 0;

  }

  if ((cc->cipher->flags & CFLAG_AESCTR) != 0) {

    if (len != sizeof(cc->ac_ctx.ctr))

      return SSH_ERR_INVALID_ARGUMENT;

    memcpy(iv, cc->ac_ctx.ctr, len);

    return 0;

  }

  if ((cc->cipher->flags & CFLAG_NONE) != 0)

    return 0;

#ifdef WITH_OPENSSL

  evplen = EVP_CIPHER_CTX_iv_length(cc->evp);

  if (evplen == 0)

    return 0;

  else if (evplen < 0)

    return SSH_ERR_LIBCRYPTO_ERROR;

  if ((size_t)evplen != len)

    return SSH_ERR_INVALID_ARGUMENT;

  if (cipher_authlen(c)) {

    if (EVP_CIPHER_CTX_ctrl(cc->evp, EVP_CTRL_GCM_IV_GEN, len,

        iv) <= 0)

      return SSH_ERR_LIBCRYPTO_ERROR;

  } else if (EVP_CIPHER_CTX_get_iv(cc->evp, iv, len) <= 0)

    return SSH_ERR_LIBCRYPTO_ERROR;

#endif

  return 0;

}

int

cipher_set_keyiv(struct sshcipher_ctx *cc, const u_char *iv, size_t len)

{

#ifdef WITH_OPENSSL

  const struct sshcipher *c = cc->cipher;

  int evplen = 0;

#endif

  if ((cc->cipher->flags & CFLAG_CHACHAPOLY) != 0)

    return 0;

  if ((cc->cipher->flags & CFLAG_NONE) != 0)

    return 0;

#ifdef WITH_OPENSSL

  evplen = EVP_CIPHER_CTX_iv_length(cc->evp);

  if (evplen <= 0)

    return SSH_ERR_LIBCRYPTO_ERROR;

  if ((size_t)evplen != len)

    return SSH_ERR_INVALID_ARGUMENT;

  if (cipher_authlen(c)) {

    /* XXX iv arg is const, but EVP_CIPHER_CTX_ctrl isn't */

    if (EVP_CIPHER_CTX_ctrl(cc->evp,

        EVP_CTRL_GCM_SET_IV_FIXED, -1, (void *)iv) <= 0)

      return SSH_ERR_LIBCRYPTO_ERROR;

  } else if (!EVP_CIPHER_CTX_set_iv(cc->evp, iv, evplen))

    return SSH_ERR_LIBCRYPTO_ERROR;

#endif

  return 0;

}