/* $NetBSD: tls_dh.c,v 1.4 2022/10/08 16:12:50 christos Exp $ */
/*++
/* NAME
/* tls_dh
/* SUMMARY
/* Diffie-Hellman parameter support
/* SYNOPSIS
/* #define TLS_INTERNAL
/* #include <tls.h>
/*
/* void tls_set_dh_from_file(path)
/* const char *path;
/*
/* void tls_auto_eecdh_curves(ctx, configured)
/* SSL_CTX *ctx;
/* char *configured;
/*
/* void tls_tmp_dh(ctx, useauto)
/* SSL_CTX *ctx;
/* int useauto;
/* DESCRIPTION
/* This module maintains parameters for Diffie-Hellman key generation.
/*
/* tls_tmp_dh() returns the configured or compiled-in FFDHE
/* group parameters.
/*
/* tls_set_dh_from_file() overrides compiled-in DH parameters
/* with those specified in the named files. The file format
/* is as expected by the PEM_read_DHparams() routine.
/*
/* tls_auto_eecdh_curves() enables negotiation of the most preferred curve
/* among the curves specified by the "configured" argument. The useauto
/* argument enables OpenSSL-builtin group selection in preference to our
/* own compiled-in group. This may interoperate better with overly strict
/* peers that accept only "standard" groups (bogus threat model).
/* DIAGNOSTICS
/* In case of error, tls_set_dh_from_file() logs a warning and
/* ignores the request.
/* LICENSE
/* .ad
/* .fi
/* This software is free. You can do with it whatever you want.
/* The original author kindly requests that you acknowledge
/* the use of his software.
/* AUTHOR(S)
/* Originally written by:
/* Lutz Jaenicke
/* BTU Cottbus
/* Allgemeine Elektrotechnik
/* Universitaetsplatz 3-4
/* D-03044 Cottbus, Germany
/*
/* Updated by:
/* Wietse Venema
/* IBM T.J. Watson Research
/* P.O. Box 704
/* Yorktown Heights, NY 10598, USA
/*--*/
/* System library. */
#include <sys_defs.h>
#ifdef USE_TLS
#include <stdio.h>
/* Utility library. */
#include <msg.h>
#include <mymalloc.h>
#include <stringops.h>
/*
* Global library
*/
#include <mail_params.h>
/* TLS library. */
#define TLS_INTERNAL
#include <tls.h>
#include <openssl/dh.h>
#ifndef OPENSSL_NO_ECDH
#include <openssl/ec.h>
#endif
#if OPENSSL_VERSION_PREREQ(3,0)
#include <openssl/decoder.h>
#endif
/* Application-specific. */
/*
* Compiled-in FFDHE (finite-field ephemeral Diffie-Hellman) parameters.
* Used when no parameters are explicitly loaded from a site-specific file.
*
* With OpenSSL 3.0 and later when no explicit parameter file is specified by
* the administrator (or the setting is "auto"), we delegate group selection
* to OpenSSL via SSL_CTX_set_dh_auto(3).
*
* Using an ASN.1 DER encoding avoids the need to explicitly manipulate the
* internal representation of DH parameter objects.
*
* The FFDHE group is now 2048-bit, as 1024 bits is increasingly considered to
* weak by clients. When greater security is required, use EECDH.
*/
/*-
* Generated via:
* $ openssl dhparam -2 -outform DER 2048 2>/dev/null |
* hexdump -ve '/1 "0x%02x, "' | fmt -73
* TODO: generate at compile-time. But that is no good for the majority of
* sites that install pre-compiled binaries, and breaks reproducible builds.
* Instead, generate at installation time and use main.cf configuration.
*/
static unsigned char builtin_der[] = {
0x30, 0x82, 0x01, 0x08, 0x02, 0x82, 0x01, 0x01, 0x00, 0xec, 0x02, 0x7b,
0x74, 0xc6, 0xd4, 0xb4, 0x89, 0x68, 0xfd, 0xbc, 0xe0, 0x82, 0xae, 0xd6,
0xf1, 0x4d, 0x93, 0xaa, 0x47, 0x07, 0x84, 0x3d, 0x86, 0xf8, 0x47, 0xf7,
0xdf, 0x08, 0x7b, 0xca, 0x04, 0xa4, 0x72, 0xec, 0x11, 0xe2, 0x38, 0x43,
0xb7, 0x94, 0xab, 0xaf, 0xe2, 0x85, 0x59, 0x43, 0x4e, 0x71, 0x85, 0xfe,
0x52, 0x0c, 0xe0, 0x1c, 0xb6, 0xc7, 0xb0, 0x1b, 0x06, 0xb3, 0x4d, 0x1b,
0x4f, 0xf6, 0x4b, 0x45, 0xbd, 0x1d, 0xb8, 0xe4, 0xa4, 0x48, 0x09, 0x28,
0x19, 0xd7, 0xce, 0xb1, 0xe5, 0x9a, 0xc4, 0x94, 0x55, 0xde, 0x4d, 0x86,
0x0f, 0x4c, 0x5e, 0x25, 0x51, 0x6c, 0x96, 0xca, 0xfa, 0xe3, 0x01, 0x69,
0x82, 0x6c, 0x8f, 0xf5, 0xe7, 0x0e, 0xb7, 0x8e, 0x52, 0xf1, 0xcf, 0x0b,
0x67, 0x10, 0xd0, 0xb3, 0x77, 0x79, 0xa4, 0xc1, 0xd0, 0x0f, 0x3f, 0xf5,
0x5c, 0x35, 0xf9, 0x46, 0xd2, 0xc7, 0xfb, 0x97, 0x6d, 0xd5, 0xbe, 0xe4,
0x8b, 0x5a, 0xf2, 0x88, 0xfa, 0x47, 0xdc, 0xc2, 0x4a, 0x4d, 0x69, 0xd3,
0x2a, 0xdf, 0x55, 0x6c, 0x5f, 0x71, 0x11, 0x1e, 0x87, 0x03, 0x68, 0xe1,
0xf4, 0x21, 0x06, 0x63, 0xd9, 0x65, 0xd4, 0x0c, 0x4d, 0xa7, 0x1f, 0x15,
0x53, 0x3a, 0x50, 0x1a, 0xf5, 0x9b, 0x50, 0x35, 0xe0, 0x16, 0xa1, 0xd7,
0xe6, 0xbf, 0xd7, 0xd9, 0xd9, 0x53, 0xe5, 0x8b, 0xf8, 0x7b, 0x45, 0x46,
0xb6, 0xac, 0x50, 0x16, 0x46, 0x42, 0xca, 0x76, 0x38, 0x4b, 0x8e, 0x83,
0xc6, 0x73, 0x13, 0x9c, 0x03, 0xd1, 0x7a, 0x3d, 0x8d, 0x99, 0x34, 0x10,
0x79, 0x67, 0x21, 0x23, 0xf9, 0x6f, 0x48, 0x9a, 0xa6, 0xde, 0xbf, 0x7f,
0x9c, 0x16, 0x53, 0xff, 0xf7, 0x20, 0x96, 0xeb, 0x34, 0xcb, 0x5b, 0x85,
0x2b, 0x7c, 0x98, 0x00, 0x23, 0x47, 0xce, 0xc2, 0x58, 0x12, 0x86, 0x2c,
0x57, 0x02, 0x01, 0x02,
};
#if OPENSSL_VERSION_PREREQ(3,0)
/* ------------------------------------- 3.0 API */
static EVP_PKEY *dhp = 0;
/* load_builtin - load compile-time FFDHE group */
static void load_builtin(void)
{
EVP_PKEY *tmp = 0;
OSSL_DECODER_CTX *d;
const unsigned char *endp = builtin_der;
size_t dlen = sizeof(builtin_der);
d = OSSL_DECODER_CTX_new_for_pkey(&tmp, "DER", NULL, "DH",
OSSL_KEYMGMT_SELECT_DOMAIN_PARAMETERS,
NULL, NULL);
/* Check decode succeeds and consumes all data (final dlen == 0) */
if (d && OSSL_DECODER_from_data(d, &endp, &dlen) && tmp && !dlen) {
dhp = tmp;
} else {
EVP_PKEY_free(tmp);
msg_warn("error loading compiled-in DH parameters");
tls_print_errors();
}
OSSL_DECODER_CTX_free(d);
}
/* tls_set_dh_from_file - set Diffie-Hellman parameters from file */
void tls_set_dh_from_file(const char *path)
{
FILE *fp;
EVP_PKEY *tmp = 0;
OSSL_DECODER_CTX *d;
/*
* This function is the first to set the DH parameters, but free any
* prior value just in case the call sequence changes some day.
*/
if (dhp) {
EVP_PKEY_free(dhp);
dhp = 0;
}
if (strcmp(path, "auto") == 0)
return;
if ((fp = fopen(path, "r")) == 0) {
msg_warn("error opening DH parameter file \"%s\": %m"
" -- using compiled-in defaults", path);
return;
}
d = OSSL_DECODER_CTX_new_for_pkey(&tmp, "PEM", NULL, "DH",
OSSL_KEYMGMT_SELECT_DOMAIN_PARAMETERS,
NULL, NULL);
if (!d || !OSSL_DECODER_from_fp(d, fp) || !tmp) {
msg_warn("error decoding DH parameters from file \"%s\""
" -- using compiled-in defaults", path);
tls_print_errors();
} else {
dhp = tmp;
}
OSSL_DECODER_CTX_free(d);
(void) fclose(fp);
}
/* tls_tmp_dh - configure FFDHE group */
void tls_tmp_dh(SSL_CTX *ctx, int useauto)
{
if (!dhp && !useauto)
load_builtin();
if (!ctx)
return;
if (dhp) {
EVP_PKEY *tmp = EVP_PKEY_dup(dhp);
if (tmp && SSL_CTX_set0_tmp_dh_pkey(ctx, tmp) > 0)
return;
EVP_PKEY_free(tmp);
msg_warn("error configuring explicit DH parameters");
tls_print_errors();
} else {
if (SSL_CTX_set_dh_auto(ctx, 1) > 0)
return;
msg_warn("error configuring auto DH parameters");
tls_print_errors();
}
}
#else /* OPENSSL_VERSION_PREREQ(3,0) */
/* ------------------------------------- 1.1.1 API */
static DH *dhp = 0;
static void load_builtin(void)
{
DH *tmp = 0;
const unsigned char *endp = builtin_der;
if (d2i_DHparams(&tmp, &endp, sizeof(builtin_der))
&& sizeof(builtin_der) == endp - builtin_der) {
dhp = tmp;
} else {
DH_free(tmp);
msg_warn("error loading compiled-in DH parameters");
tls_print_errors();
}
}
/* tls_set_dh_from_file - set Diffie-Hellman parameters from file */
void tls_set_dh_from_file(const char *path)
{
FILE *fp;
/*
* This function is the first to set the DH parameters, but free any
* prior value just in case the call sequence changes some day.
*/
if (dhp) {
DH_free(dhp);
dhp = 0;
}
/*
* Forwards compatibility, support "auto" by using the builtin group when
* OpenSSL is < 3.0 and does not support automatic FFDHE group selection.
*/
if (strcmp(path, "auto") == 0)
return;
if ((fp = fopen(path, "r")) == 0) {
msg_warn("cannot load DH parameters from file %s: %m"
" -- using compiled-in defaults", path);
return;
}
if ((dhp = PEM_read_DHparams(fp, 0, 0, 0)) == 0) {
msg_warn("cannot load DH parameters from file %s"
" -- using compiled-in defaults", path);
tls_print_errors();
}
(void) fclose(fp);
}
/* tls_tmp_dh - configure FFDHE group */
void tls_tmp_dh(SSL_CTX *ctx, int useauto)
{
if (!dhp)
load_builtin();
if (!ctx || !dhp || SSL_CTX_set_tmp_dh(ctx, dhp) > 0)
return;
msg_warn("error configuring explicit DH parameters");
tls_print_errors();
}
#endif /* OPENSSL_VERSION_PREREQ(3,0) */
/* ------------------------------------- Common API */
void tls_auto_eecdh_curves(SSL_CTX *ctx, const char *configured)
{
#ifndef OPENSSL_NO_ECDH
SSL_CTX *tmpctx;
int *nids;
int space = 5;
int n = 0;
int unknown = 0;
char *save;
char *curves;
char *curve;
if ((tmpctx = SSL_CTX_new(TLS_method())) == 0) {
msg_warn("cannot allocate temp SSL_CTX, using default ECDHE curves");
tls_print_errors();
return;
}
nids = mymalloc(space * sizeof(int));
curves = save = mystrdup(configured);
#define RETURN do { \
myfree(save); \
myfree(nids); \
SSL_CTX_free(tmpctx); \
return; \
} while (0)
while ((curve = mystrtok(&curves, CHARS_COMMA_SP)) != 0) {
int nid = EC_curve_nist2nid(curve);
if (nid == NID_undef)
nid = OBJ_sn2nid(curve);
if (nid == NID_undef)
nid = OBJ_ln2nid(curve);
if (nid == NID_undef) {
msg_warn("ignoring unknown ECDHE curve \"%s\"",
curve);
continue;
}
/*
* Validate the NID by trying it as the sole EC curve for a
* throw-away SSL context. Silently skip unsupported code points.
* This way, we can list X25519 and X448 as soon as the nids are
* assigned, and before the supporting code is implemented. They'll
* be silently skipped when not yet supported.
*/
if (SSL_CTX_set1_curves(tmpctx, &nid, 1) <= 0) {
++unknown;
continue;
}
if (++n > space) {
space *= 2;
nids = myrealloc(nids, space * sizeof(int));
}
nids[n - 1] = nid;
}
if (n == 0) {
if (unknown > 0)
msg_warn("none of the configured ECDHE curves are supported");
RETURN;
}
if (SSL_CTX_set1_curves(ctx, nids, n) <= 0) {
msg_warn("failed to configure ECDHE curves");
tls_print_errors();
RETURN;
}
RETURN;
#endif
}
#ifdef TEST
int main(int unused_argc, char **unused_argv)
{
tls_tmp_dh(0, 0);
return (dhp == 0);
}
#endif
#endif