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ESNI: initial build/setup

Closes #4011
This commit is contained in:
Niall 2019-06-04 15:53:02 +01:00 committed by Daniel Stenberg
parent 475324b272
commit 0f48055c40
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8 changed files with 220 additions and 1 deletions

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@ -49,6 +49,7 @@ CURL_CHECK_OPTION_CURLDEBUG
CURL_CHECK_OPTION_SYMBOL_HIDING
CURL_CHECK_OPTION_ARES
CURL_CHECK_OPTION_RT
CURL_CHECK_OPTION_ESNI
XC_CHECK_PATH_SEPARATOR
@ -4497,6 +4498,36 @@ if test "$enable_altsvc" = "yes"; then
experimental="$experimental alt-svc"
fi
dnl *************************************************************
dnl check whether ESNI support, if desired, is actually available
dnl
if test "x$want_esni" != "xno"; then
AC_MSG_CHECKING([whether ESNI support is available])
dnl assume NOT and look for sufficient condition
ESNI_ENABLED=0
ESNI_SUPPORT=''
dnl OpenSSL with a chosen ESNI function should be enough
dnl so more exhaustive checking seems unnecessary for now
if test "x$OPENSSL_ENABLED" == "x1"; then
AC_CHECK_FUNCS(SSL_get_esni_status,
ESNI_SUPPORT="ESNI support available (OpenSSL with SSL_get_esni_status)"
ESNI_ENABLED=1)
dnl add 'elif' chain here for additional implementations
fi
dnl now deal with whatever we found
if test "x$ESNI_ENABLED" == "x1"; then
AC_DEFINE(USE_ESNI, 1, [if ESNI support is available])
AC_MSG_RESULT($ESNI_SUPPORT)
experimental="$experimental ESNI"
else
AC_MSG_ERROR([--enable-esni ignored: No ESNI support found])
fi
fi
dnl ************************************************************
dnl hiding of library internal symbols
dnl
@ -4618,6 +4649,10 @@ if test "x$OPENSSL_ENABLED" = "x1" -o "x$GNUTLS_ENABLED" = "x1" \
SUPPORT_FEATURES="$SUPPORT_FEATURES HTTPS-proxy"
fi
if test "x$ESNI_ENABLED" = "x1"; then
SUPPORT_FEATURES="$SUPPORT_FEATURES ESNI"
fi
AC_SUBST(SUPPORT_FEATURES)
dnl For supported protocols in pkg-config file
@ -4801,6 +4836,7 @@ AC_MSG_NOTICE([Configured to build curl/libcurl:
Alt-svc: ${curl_altsvc_msg}
HTTP2: ${curl_h2_msg}
HTTP3: ${curl_h3_msg}
ESNI: ${curl_esni_msg}
Protocols: ${SUPPORT_PROTOCOLS}
Features: ${SUPPORT_FEATURES}
])

139
docs/ESNI.md Normal file
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@ -0,0 +1,139 @@
# TLS: ESNI support in curl and libcurl
## Summary
**ESNI** means **Encrypted Server Name Indication**, a TLS 1.3
extension which is currently the subject of an
[IETF Draft][tlsesni].
This file is intended to show the latest current state of ESNI support
in **curl** and **libcurl**.
At end of August 2019, an [experimental fork of curl][niallorcurl],
built using an [experimental fork of OpenSSL][sftcdopenssl], which in
turn provided an implementation of ESNI, was demonstrated
interoperating with a server belonging to the [DEfO
Project][defoproj].
Further sections here describe
- resources needed for building and demonstrating **curl** support
for ESNI,
- progress to date,
- TODO items, and
- additional details of specific stages of the progress.
## Resources needed
To build and demonstrate ESNI support in **curl** and/or **libcurl**,
you will need
- a TLS library, supported by **libcurl**, which implements ESNI;
- an edition of **curl** and/or **libcurl** which supports the ESNI
implementation of the chosen TLS library;
- an environment for building and running **curl**, and at least
building **OpenSSL**;
- a server, supporting ESNI, against which to run a demonstration
and perhaps a specific target URL;
- some instructions.
The following set of resources is currently known to be available.
| Set | Component | Location | Remarks |
|:-----|:-------------|:------------------------------|:-------------------------------------------|
| DEfO | TLS library | [sftcd/openssl][sftcdopenssl] | Tag *esni-2019-08-30* avoids bleeding edge |
| | curl fork | [niallor/curl][niallorcurl] | Tag *esni-2019-08-30* likewise |
| | instructions | [ESNI-README][niallorreadme] | |
## Progress
### PR 4011 (Jun 2019) expected in curl release 7.67.0 (Oct 2019)
- Details [below](#pr4011);
- New **curl** feature: `CURL_VERSION_ESNI`;
- New configuration option: `--enable-esni`;
- Build-time check for availability of resources needed for ESNI
support;
- Pre-processor symbol `USE_ESNI` for conditional compilation of
ESNI support code, subject to configuration option and
availability of needed resources.
## TODO
- (next PR) Add libcurl options to set ESNI parameters.
- (next PR) Add curl tool command line options to set ESNI parameters.
- (WIP) Extend DoH functions so that published ESNI parameters can be
retrieved from DNS instead of being required as options.
- (WIP) Work with OpenSSL community to finalize ESNI API.
- Track OpenSSL ESNI API in libcurl
- Identify and implement any changes needed for CMake.
- Optimize build-time checking of available resources.
- Encourage ESNI support work on other TLS/SSL backends.
## Additional detail
### PR 4011
**TLS: Provide ESNI support framework for curl and libcurl**
The proposed change provides a framework to facilitate work to
implement ESNI support in curl and libcurl. It is not intended
either to provide ESNI functionality or to favour any particular
TLS-providing backend. Specifically, the change reserves a
feature bit for ESNI support (symbol `CURL_VERSION_ESNI`),
implements setting and reporting of this bit, includes dummy
book-keeping for the symbol, adds a build-time configuration
option (`--enable-esni`), provides an extensible check for
resources available to provide ESNI support, and defines a
compiler pre-processor symbol (`USE_ESNI`) accordingly.
Proposed-by: @niallor (Niall O'Reilly)\
Encouraged-by: @sftcd (Stephen Farrell)\
See-also: [this message](https://curl.haxx.se/mail/lib-2019-05/0108.html)
Limitations:
- Book-keeping (symbols-in-versions) needs real release number, not 'DUMMY'.
- Framework is incomplete, as it covers autoconf, but not CMake.
- Check for available resources, although extensible, refers only to
specific work in progress ([described
here](https://github.com/sftcd/openssl/tree/master/esnistuff)) to
implement ESNI for OpenSSL, as this is the immediate motivation
for the proposed change.
## References
CloudFlare blog: [Encrypting SNI: Fixing One of the Core Internet Bugs][corebug]
Cloudflare blog: [Encrypt it or lose it: how encrypted SNI works][esniworks]
IETF Draft: [Encrypted Server Name Indication for TLS 1.3][tlsesni]
---
[tlsesni]: https://datatracker.ietf.org/doc/draft-ietf-tls-esni/
[esniworks]: https://blog.cloudflare.com/encrypted-sni/
[corebug]: https://blog.cloudflare.com/esni/
[defoproj]: https://defo.ie/
[sftcdopenssl]: https://github.com/sftcd/openssl/
[niallorcurl]: https://github.com/niallor/curl/
[niallorreadme]: https://github.com/niallor/curl/blob/master/ESNI-README.md

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@ -53,6 +53,7 @@ EXTRA_DIST = \
CODE_STYLE.md \
CONTRIBUTE.md \
DEPRECATE.md \
ESNI.md \
EXPERIMENTAL.md \
FAQ \
FEATURES \

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@ -927,6 +927,7 @@ CURL_VERSION_BROTLI 7.57.0
CURL_VERSION_CONV 7.15.4
CURL_VERSION_CURLDEBUG 7.19.6
CURL_VERSION_DEBUG 7.10.6
CURL_VERSION_ESNI 7.67.0
CURL_VERSION_GSSAPI 7.38.0
CURL_VERSION_GSSNEGOTIATE 7.10.6 7.38.0
CURL_VERSION_HTTP2 7.33.0

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@ -2800,6 +2800,8 @@ typedef struct {
#define CURL_VERSION_ALTSVC (1<<24) /* Alt-Svc handling built-in */
#define CURL_VERSION_HTTP3 (1<<25) /* HTTP3 support built-in */
#define CURL_VERSION_ESNI (1<<26) /* ESNI support */
/*
* NAME curl_version_info()
*

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@ -366,6 +366,9 @@ static curl_version_info_data version_info = {
#endif
#if defined(USE_ALTSVC)
| CURL_VERSION_ALTSVC
#endif
#ifdef USE_ESNI
| CURL_VERSION_ESNI
#endif
,
NULL, /* ssl_version */

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@ -5,7 +5,7 @@
# | (__| |_| | _ <| |___
# \___|\___/|_| \_\_____|
#
# Copyright (C) 1998 - 2018, Daniel Stenberg, <daniel@haxx.se>, et al.
# Copyright (C) 1998 - 2019, Daniel Stenberg, <daniel@haxx.se>, et al.
#
# This software is licensed as described in the file COPYING, which
# you should have received as part of this distribution. The terms
@ -648,3 +648,39 @@ AC_DEFUN([CURL_CHECK_NTLM_WB], [
NTLM_WB_ENABLED=1
fi
])
dnl CURL_CHECK_OPTION_ESNI
dnl -----------------------------------------------------
dnl Verify whether configure has been invoked with option
dnl --enable-esni or --disable-esni, and set
dnl shell variable want_esni as appropriate.
AC_DEFUN([CURL_CHECK_OPTION_ESNI], [
AC_MSG_CHECKING([whether to enable ESNI support])
OPT_ESNI="default"
AC_ARG_ENABLE(esni,
AC_HELP_STRING([--enable-esni],[Enable ESNI support])
AC_HELP_STRING([--disable-esni],[Disable ESNI support]),
OPT_ESNI=$enableval)
case "$OPT_ESNI" in
no)
dnl --disable-esni option used
want_esni="no"
curl_esni_msg="no (--enable-esni)"
AC_MSG_RESULT([no])
;;
default)
dnl configure option not specified
want_esni="no"
curl_esni_msg="no (--enable-esni)"
AC_MSG_RESULT([no])
;;
*)
dnl --enable-esni option used
want_esni="yes"
curl_esni_msg="enabled (--disable-esni)"
experimental="esni"
AC_MSG_RESULT([yes])
;;
esac
])

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@ -540,6 +540,7 @@ static const struct feat feats[] = {
{"MultiSSL", CURL_VERSION_MULTI_SSL},
{"PSL", CURL_VERSION_PSL},
{"alt-svc", CURL_VERSION_ALTSVC},
{"ESNI", CURL_VERSION_ESNI},
};
void tool_help(void)