[Openvpn-devel,v3] Require AEAD support in the crypto library

  All supported crypto libraries have AEAD support and with our
ncp/de facto default cipher AES-256-GCM we do not want to support
the obscure corner case of a library with disabled AEAD.

Signed-off-by: Arne Schwabe <arne@rfc2549.org>

Patch V2: Remove three instances of (harmless) #ifdef Steffan spotted
          that can be removed now too.
---
 config-msvc.h                |  1 -
 configure.ac                 |  7 ++-----
 src/openvpn/crypto.c         | 11 -----------
 src/openvpn/crypto_mbedtls.c | 14 --------------
 src/openvpn/crypto_openssl.c | 26 ++------------------------
 src/openvpn/crypto_openssl.h |  4 ----
 src/openvpn/options.c        |  6 ------
 7 files changed, 4 insertions(+), 65 deletions(-)
  

Hi,

On 20-07-2020 14:17, Arne Schwabe wrote:
> All supported crypto libraries have AEAD support and with our
> ncp/de facto default cipher AES-256-GCM we do not want to support
> the obscure corner case of a library with disabled AEAD.
> 
> Signed-off-by: Arne Schwabe <arne@rfc2549.org>
> 
> Patch V2: Remove three instances of (harmless) #ifdef Steffan spotted
>           that can be removed now too.
> ---
>  config-msvc.h                |  1 -
>  configure.ac                 |  7 ++-----
>  src/openvpn/crypto.c         | 11 -----------
>  src/openvpn/crypto_mbedtls.c | 14 --------------
>  src/openvpn/crypto_openssl.c | 26 ++------------------------
>  src/openvpn/crypto_openssl.h |  4 ----
>  src/openvpn/options.c        |  6 ------
>  7 files changed, 4 insertions(+), 65 deletions(-)
> 
> diff --git a/config-msvc.h b/config-msvc.h
> index 875da4a6..8ef48979 100644
> --- a/config-msvc.h
> +++ b/config-msvc.h
> @@ -5,7 +5,6 @@
>  #define ENABLE_DEF_AUTH 1
>  #define ENABLE_PF 1
>  #define ENABLE_CRYPTO_OPENSSL 1
> -#define HAVE_AEAD_CIPHER_MODES 1
>  #define ENABLE_DEBUG 1
>  #define ENABLE_EUREPHIA 1
>  #define ENABLE_FRAGMENT 1
> diff --git a/configure.ac b/configure.ac
> index d1db0a21..43f78fb7 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -907,11 +907,10 @@ if test "${with_crypto_library}" = "openssl"; then
>  		AC_DEFINE([HAVE_OPENSSL_ENGINE], [1], [OpenSSL engine support available])
>  	fi
>  
> -	have_crypto_aead_modes="yes"
>  	AC_CHECK_FUNC(
>  		[EVP_aes_256_gcm],
>  		,
> -		[have_crypto_aead_modes="no"]
> +		[AC_MSG_ERROR([OpenSSL check for AES-256-GCM support failed])]
>  	)
>  
>      # All supported OpenSSL version (>= 1.0.2)
> @@ -1005,14 +1004,13 @@ elif test "${with_crypto_library}" = "mbedtls"; then
>  		[AC_MSG_ERROR([mbed TLS 2.y.z required])]
>  	)
>  
> -	have_crypto_aead_modes="yes"
>  	AC_CHECK_FUNCS(
>  		[ \
>  			mbedtls_cipher_write_tag \
>  			mbedtls_cipher_check_tag \
>  		],
>  		,
> -		[have_crypto_aead_modes="no"; break]
> +		[AC_MSG_ERROR([mbed TLS check for AEAD support failed])]
>  	)
>  
>  	have_export_keying_material="yes"
> @@ -1227,7 +1225,6 @@ test "${enable_pf}" = "yes" && AC_DEFINE([ENABLE_PF], [1], [Enable internal pack
>  test "${enable_strict_options}" = "yes" && AC_DEFINE([ENABLE_STRICT_OPTIONS_CHECK], [1], [Enable strict options check between peers])
>  
>  test "${enable_crypto_ofb_cfb}" = "yes" && AC_DEFINE([ENABLE_OFB_CFB_MODE], [1], [Enable OFB and CFB cipher modes])
> -test "${have_crypto_aead_modes}" = "yes" && AC_DEFINE([HAVE_AEAD_CIPHER_MODES], [1], [Use crypto library])
>  if test "${have_export_keying_material}" = "yes"; then
>  	AC_DEFINE(
>  		[HAVE_EXPORT_KEYING_MATERIAL], [1],
> diff --git a/src/openvpn/crypto.c b/src/openvpn/crypto.c
> index bbf47ef7..e92a0dc1 100644
> --- a/src/openvpn/crypto.c
> +++ b/src/openvpn/crypto.c
> @@ -64,7 +64,6 @@ static void
>  openvpn_encrypt_aead(struct buffer *buf, struct buffer work,
>                       struct crypto_options *opt)
>  {
> -#ifdef HAVE_AEAD_CIPHER_MODES
>      struct gc_arena gc;
>      int outlen = 0;
>      const struct key_ctx *ctx = &opt->key_ctx_bi.encrypt;
> @@ -152,9 +151,6 @@ err:
>      buf->len = 0;
>      gc_free(&gc);
>      return;
> -#else /* HAVE_AEAD_CIPHER_MODES */
> -    ASSERT(0);
> -#endif /* ifdef HAVE_AEAD_CIPHER_MODES */
>  }
>  
>  static void
> @@ -361,7 +357,6 @@ openvpn_decrypt_aead(struct buffer *buf, struct buffer work,
>                       struct crypto_options *opt, const struct frame *frame,
>                       const uint8_t *ad_start)
>  {
> -#ifdef HAVE_AEAD_CIPHER_MODES
>      static const char error_prefix[] = "AEAD Decrypt error";
>      struct packet_id_net pin = { 0 };
>      const struct key_ctx *ctx = &opt->key_ctx_bi.decrypt;
> @@ -482,10 +477,6 @@ error_exit:
>      buf->len = 0;
>      gc_free(&gc);
>      return false;
> -#else /* HAVE_AEAD_CIPHER_MODES */
> -    ASSERT(0);
> -    return false;
> -#endif /* ifdef HAVE_AEAD_CIPHER_MODES */
>  }
>  
>  /*
> @@ -1104,7 +1095,6 @@ test_crypto(struct crypto_options *co, struct frame *frame)
>      /* init work */
>      ASSERT(buf_init(&work, FRAME_HEADROOM(frame)));
>  
> -#ifdef HAVE_AEAD_CIPHER_MODES
>      /* init implicit IV */
>      {
>          const cipher_kt_t *cipher =
> @@ -1126,7 +1116,6 @@ test_crypto(struct crypto_options *co, struct frame *frame)
>              co->key_ctx_bi.decrypt.implicit_iv_len = impl_iv_len;
>          }
>      }
> -#endif /* ifdef HAVE_AEAD_CIPHER_MODES */
>  
>      msg(M_INFO, "Entering " PACKAGE_NAME " crypto self-test mode.");
>      for (i = 1; i <= TUN_MTU_SIZE(frame); ++i)
> diff --git a/src/openvpn/crypto_mbedtls.c b/src/openvpn/crypto_mbedtls.c
> index bb752557..19a87eb4 100644
> --- a/src/openvpn/crypto_mbedtls.c
> +++ b/src/openvpn/crypto_mbedtls.c
> @@ -530,12 +530,10 @@ cipher_kt_block_size(const mbedtls_cipher_info_t *cipher_kt)
>  int
>  cipher_kt_tag_size(const mbedtls_cipher_info_t *cipher_kt)
>  {
> -#ifdef HAVE_AEAD_CIPHER_MODES
>      if (cipher_kt && cipher_kt_mode_aead(cipher_kt))
>      {
>          return OPENVPN_AEAD_TAG_LENGTH;
>      }
> -#endif
>      return 0;
>  }
>  
> @@ -632,7 +630,6 @@ cipher_ctx_iv_length(const mbedtls_cipher_context_t *ctx)
>  int
>  cipher_ctx_get_tag(cipher_ctx_t *ctx, uint8_t *tag, int tag_len)
>  {
> -#ifdef HAVE_AEAD_CIPHER_MODES
>      if (tag_len > SIZE_MAX)
>      {
>          return 0;
> @@ -644,9 +641,6 @@ cipher_ctx_get_tag(cipher_ctx_t *ctx, uint8_t *tag, int tag_len)
>      }
>  
>      return 1;
> -#else  /* ifdef HAVE_AEAD_CIPHER_MODES */
> -    ASSERT(0);
> -#endif /* HAVE_AEAD_CIPHER_MODES */
>  }
>  
>  int
> @@ -688,7 +682,6 @@ cipher_ctx_reset(mbedtls_cipher_context_t *ctx, const uint8_t *iv_buf)
>  int
>  cipher_ctx_update_ad(cipher_ctx_t *ctx, const uint8_t *src, int src_len)
>  {
> -#ifdef HAVE_AEAD_CIPHER_MODES
>      if (src_len > SIZE_MAX)
>      {
>          return 0;
> @@ -700,9 +693,6 @@ cipher_ctx_update_ad(cipher_ctx_t *ctx, const uint8_t *src, int src_len)
>      }
>  
>      return 1;
> -#else  /* ifdef HAVE_AEAD_CIPHER_MODES */
> -    ASSERT(0);
> -#endif /* HAVE_AEAD_CIPHER_MODES */
>  }
>  
>  int
> @@ -741,7 +731,6 @@ int
>  cipher_ctx_final_check_tag(mbedtls_cipher_context_t *ctx, uint8_t *dst,
>                             int *dst_len, uint8_t *tag, size_t tag_len)
>  {
> -#ifdef HAVE_AEAD_CIPHER_MODES
>      size_t olen = 0;
>  
>      if (MBEDTLS_DECRYPT != ctx->operation)
> @@ -773,9 +762,6 @@ cipher_ctx_final_check_tag(mbedtls_cipher_context_t *ctx, uint8_t *dst,
>      }
>  
>      return 1;
> -#else  /* ifdef HAVE_AEAD_CIPHER_MODES */
> -    ASSERT(0);
> -#endif /* HAVE_AEAD_CIPHER_MODES */
>  }
>  
>  void
> diff --git a/src/openvpn/crypto_openssl.c b/src/openvpn/crypto_openssl.c
> index 161a189e..c47c2f3c 100644
> --- a/src/openvpn/crypto_openssl.c
> +++ b/src/openvpn/crypto_openssl.c
> @@ -301,9 +301,7 @@ show_available_ciphers(void)
>  #ifdef ENABLE_OFB_CFB_MODE
>                         || cipher_kt_mode_ofb_cfb(cipher)
>  #endif
> -#ifdef HAVE_AEAD_CIPHER_MODES
>                         || cipher_kt_mode_aead(cipher)
> -#endif
>                         ))
>          {
>              cipher_list[num_ciphers++] = cipher;
> @@ -710,11 +708,8 @@ bool
>  cipher_kt_mode_cbc(const cipher_kt_t *cipher)
>  {
>      return cipher && cipher_kt_mode(cipher) == OPENVPN_MODE_CBC
> -#ifdef EVP_CIPH_FLAG_AEAD_CIPHER
>             /* Exclude AEAD cipher modes, they require a different API */
> -           && !(EVP_CIPHER_flags(cipher) & EVP_CIPH_FLAG_AEAD_CIPHER)
> -#endif
> -    ;
> +           && !(EVP_CIPHER_flags(cipher) & EVP_CIPH_FLAG_AEAD_CIPHER);
>  }
>  
>  bool
> @@ -722,17 +717,13 @@ cipher_kt_mode_ofb_cfb(const cipher_kt_t *cipher)
>  {
>      return cipher && (cipher_kt_mode(cipher) == OPENVPN_MODE_OFB
>                        || cipher_kt_mode(cipher) == OPENVPN_MODE_CFB)
> -#ifdef EVP_CIPH_FLAG_AEAD_CIPHER
>             /* Exclude AEAD cipher modes, they require a different API */
> -           && !(EVP_CIPHER_flags(cipher) & EVP_CIPH_FLAG_AEAD_CIPHER)
> -#endif
> -    ;
> +           && !(EVP_CIPHER_flags(cipher) & EVP_CIPH_FLAG_AEAD_CIPHER);
>  }
>  
>  bool
>  cipher_kt_mode_aead(const cipher_kt_t *cipher)
>  {
> -#ifdef HAVE_AEAD_CIPHER_MODES
>      if (cipher)
>      {
>          switch (EVP_CIPHER_nid(cipher))
> @@ -746,7 +737,6 @@ cipher_kt_mode_aead(const cipher_kt_t *cipher)
>                  return true;
>          }
>      }
> -#endif
>  
>      return false;
>  }
> @@ -806,11 +796,7 @@ cipher_ctx_iv_length(const EVP_CIPHER_CTX *ctx)
>  int
>  cipher_ctx_get_tag(EVP_CIPHER_CTX *ctx, uint8_t *tag_buf, int tag_size)
>  {
> -#ifdef HAVE_AEAD_CIPHER_MODES
>      return EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_GET_TAG, tag_size, tag_buf);
> -#else
> -    ASSERT(0);
> -#endif
>  }
>  
>  int
> @@ -841,16 +827,12 @@ cipher_ctx_reset(EVP_CIPHER_CTX *ctx, const uint8_t *iv_buf)
>  int
>  cipher_ctx_update_ad(EVP_CIPHER_CTX *ctx, const uint8_t *src, int src_len)
>  {
> -#ifdef HAVE_AEAD_CIPHER_MODES
>      int len;
>      if (!EVP_CipherUpdate(ctx, NULL, &len, src, src_len))
>      {
>          crypto_msg(M_FATAL, "%s: EVP_CipherUpdate() failed", __func__);
>      }
>      return 1;
> -#else  /* ifdef HAVE_AEAD_CIPHER_MODES */
> -    ASSERT(0);
> -#endif
>  }
>  
>  int
> @@ -874,7 +856,6 @@ int
>  cipher_ctx_final_check_tag(EVP_CIPHER_CTX *ctx, uint8_t *dst, int *dst_len,
>                             uint8_t *tag, size_t tag_len)
>  {
> -#ifdef HAVE_AEAD_CIPHER_MODES
>      ASSERT(tag_len < SIZE_MAX);
>      if (!EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_GCM_SET_TAG, tag_len, tag))
>      {
> @@ -882,9 +863,6 @@ cipher_ctx_final_check_tag(EVP_CIPHER_CTX *ctx, uint8_t *dst, int *dst_len,
>      }
>  
>      return cipher_ctx_final(ctx, dst, dst_len);
> -#else  /* ifdef HAVE_AEAD_CIPHER_MODES */
> -    ASSERT(0);
> -#endif
>  }
>  
>  void
> diff --git a/src/openvpn/crypto_openssl.h b/src/openvpn/crypto_openssl.h
> index 4694ee08..e6f8f537 100644
> --- a/src/openvpn/crypto_openssl.h
> +++ b/src/openvpn/crypto_openssl.h
> @@ -61,13 +61,9 @@ typedef HMAC_CTX hmac_ctx_t;
>  /** Cipher is in CFB mode */
>  #define OPENVPN_MODE_CFB        EVP_CIPH_CFB_MODE
>  
> -#ifdef HAVE_AEAD_CIPHER_MODES
> -
>  /** Cipher is in GCM mode */
>  #define OPENVPN_MODE_GCM        EVP_CIPH_GCM_MODE
>  
> -#endif /* HAVE_AEAD_CIPHER_MODES */
> -
>  /** Cipher should encrypt */
>  #define OPENVPN_OP_ENCRYPT      1
>  
> diff --git a/src/openvpn/options.c b/src/openvpn/options.c
> index 04518bf5..94308a8e 100644
> --- a/src/openvpn/options.c
> +++ b/src/openvpn/options.c
> @@ -104,9 +104,7 @@ const char title_string[] =
>      " [MH/RECVDA]"
>  #endif
>  #endif
> -#ifdef HAVE_AEAD_CIPHER_MODES
>      " [AEAD]"
> -#endif
>      " built on " __DATE__
>  ;
>  
> @@ -871,11 +869,7 @@ init_options(struct options *o, const bool init_gc)
>      o->scheduled_exit_interval = 5;
>  #endif
>      o->ciphername = "BF-CBC";
> -#ifdef HAVE_AEAD_CIPHER_MODES /* IV_NCP=2 requires GCM support */
>      o->ncp_enabled = true;
> -#else
> -    o->ncp_enabled = false;
> -#endif
>      o->ncp_ciphers = "AES-256-GCM:AES-128-GCM";
>      o->authname = "SHA1";
>      o->prng_hash = "SHA1";
> 

Thanks. This looks good to me now, and passes travis and basic local tests.

Acked-by: Steffan Karger <steffan.karger@foxcrypto.com>

-Steffan
  

Quick sanity check on FreeBSD/1.0.2s, Linux/1.1.1g, Linux/mbedTLS
(client side only).  All good.

Your patch has been applied to the master branch.

commit 94edc7c5dd3cf8988df15fe4d7bd6cba9486b2a6
Author: Arne Schwabe
Date:   Mon Jul 20 14:17:04 2020 +0200

     Require AEAD support in the crypto library

     Signed-off-by: Arne Schwabe <arne@rfc2549.org>
     Acked-by: Steffan Karger <steffan.karger@foxcrypto.com>
     Message-Id: <20200720121704.20333-1-arne@rfc2549.org>
     URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg20506.html
     Signed-off-by: Gert Doering <gert@greenie.muc.de>


--
kind regards,

Gert Doering