nhyatt/putty-source
1
0
Fork 0
mirror of https://git.tartarus.org/simon/putty.git synced 2025-01-09 09:27:59 +00:00
Code Issues Projects Releases Wiki Activity
20a9912c7c
putty-source/ssh2kex-server.c
Simon Tatham ece788240c Introduce a vtable system for prime generation. 
The functions primegen() and primegen_add_progress_phase() are gone.
In their place is a small vtable system with two methods corresponding
to them, plus the usual admin of allocating and freeing contexts.

This API change is the starting point for being able to drop in
different prime generation algorithms at run time in response to user
configuration.
2020-03-01 20:09:01 +00:00

330 lines
12 KiB
C
Raw Blame History

/*
* Server side of key exchange for the SSH-2 transport protocol (RFC 4253).
*/
#include <assert.h>
#include "putty.h"
#include "ssh.h"
#include "sshbpp.h"
#include "sshppl.h"
#include "sshcr.h"
#include "sshserver.h"
#include "sshkeygen.h"
#include "storage.h"
#include "ssh2transport.h"
#include "mpint.h"
void ssh2_transport_provide_hostkeys(PacketProtocolLayer *ppl,
ssh_key *const *hostkeys, int nhostkeys)
{
struct ssh2_transport_state *s =
container_of(ppl, struct ssh2_transport_state, ppl);
s->hostkeys = hostkeys;
s->nhostkeys = nhostkeys;
}
static strbuf *finalise_and_sign_exhash(struct ssh2_transport_state *s)
{
strbuf *sb;
ssh2transport_finalise_exhash(s);
sb = strbuf_new();
ssh_key_sign(
s->hkey, make_ptrlen(s->exchange_hash, s->kex_alg->hash->hlen),
0, BinarySink_UPCAST(sb));
return sb;
}
void ssh2kex_coroutine(struct ssh2_transport_state *s, bool *aborted)
{
PacketProtocolLayer *ppl = &s->ppl; /* for ppl_logevent */
PktIn *pktin;
PktOut *pktout;
crBegin(s->crStateKex);
{
int i;
for (i = 0; i < s->nhostkeys; i++)
if (ssh_key_alg(s->hostkeys[i]) == s->hostkey_alg) {
s->hkey = s->hostkeys[i];
break;
}
assert(s->hkey);
}
strbuf_clear(s->hostkeyblob);
ssh_key_public_blob(s->hkey, BinarySink_UPCAST(s->hostkeyblob));
s->hostkeydata = ptrlen_from_strbuf(s->hostkeyblob);
put_stringpl(s->exhash, s->hostkeydata);
if (s->kex_alg->main_type == KEXTYPE_DH) {
/*
* If we're doing Diffie-Hellman group exchange, start by
* waiting for the group request.
*/
if (dh_is_gex(s->kex_alg)) {
ppl_logevent("Doing Diffie-Hellman group exchange");
s->ppl.bpp->pls->kctx = SSH2_PKTCTX_DHGEX;
crMaybeWaitUntilV((pktin = ssh2_transport_pop(s)) != NULL);
if (pktin->type != SSH2_MSG_KEX_DH_GEX_REQUEST &&
pktin->type != SSH2_MSG_KEX_DH_GEX_REQUEST_OLD) {
ssh_proto_error(s->ppl.ssh, "Received unexpected packet when "
"expecting Diffie-Hellman group exchange "
"request, type %d (%s)", pktin->type,
ssh2_pkt_type(s->ppl.bpp->pls->kctx,
s->ppl.bpp->pls->actx,
pktin->type));
*aborted = true;
return;
}
if (pktin->type != SSH2_MSG_KEX_DH_GEX_REQUEST_OLD) {
s->dh_got_size_bounds = true;
s->dh_min_size = get_uint32(pktin);
s->pbits = get_uint32(pktin);
s->dh_max_size = get_uint32(pktin);
} else {
s->dh_got_size_bounds = false;
s->pbits = get_uint32(pktin);
}
/*
* This is a hopeless strategy for making a secure DH
* group! It's good enough for testing a client against,
* but not for serious use.
*/
PrimeGenerationContext *pgc = primegen_new_context(
&primegen_probabilistic);
ProgressReceiver null_progress;
null_progress.vt = &null_progress_vt;
s->p = primegen_generate(pgc, pcs_new(s->pbits), &null_progress);
primegen_free_context(pgc);
s->g = mp_from_integer(2);
s->dh_ctx = dh_setup_gex(s->p, s->g);
s->kex_init_value = SSH2_MSG_KEX_DH_GEX_INIT;
s->kex_reply_value = SSH2_MSG_KEX_DH_GEX_REPLY;
pktout = ssh_bpp_new_pktout(s->ppl.bpp, SSH2_MSG_KEX_DH_GEX_GROUP);
put_mp_ssh2(pktout, s->p);
put_mp_ssh2(pktout, s->g);
pq_push(s->ppl.out_pq, pktout);
} else {
s->ppl.bpp->pls->kctx = SSH2_PKTCTX_DHGROUP;
s->dh_ctx = dh_setup_group(s->kex_alg);
s->kex_init_value = SSH2_MSG_KEXDH_INIT;
s->kex_reply_value = SSH2_MSG_KEXDH_REPLY;
ppl_logevent("Using Diffie-Hellman with standard group \"%s\"",
s->kex_alg->groupname);
}
ppl_logevent("Doing Diffie-Hellman key exchange with hash %s",
ssh_hash_alg(s->exhash)->text_name);
/*
* Generate e for Diffie-Hellman.
*/
s->e = dh_create_e(s->dh_ctx, s->nbits * 2);
/*
* Wait to receive f.
*/
crMaybeWaitUntilV((pktin = ssh2_transport_pop(s)) != NULL);
if (pktin->type != s->kex_init_value) {
ssh_proto_error(s->ppl.ssh, "Received unexpected packet when "
"expecting Diffie-Hellman initial packet, "
"type %d (%s)", pktin->type,
ssh2_pkt_type(s->ppl.bpp->pls->kctx,
s->ppl.bpp->pls->actx,
pktin->type));
*aborted = true;
return;
}
s->f = get_mp_ssh2(pktin);
if (get_err(pktin)) {
ssh_proto_error(s->ppl.ssh,
"Unable to parse Diffie-Hellman initial packet");
*aborted = true;
return;
}
{
const char *err = dh_validate_f(s->dh_ctx, s->f);
if (err) {
ssh_proto_error(s->ppl.ssh, "Diffie-Hellman initial packet "
"failed validation: %s", err);
*aborted = true;
return;
}
}
s->K = dh_find_K(s->dh_ctx, s->f);
if (dh_is_gex(s->kex_alg)) {
if (s->dh_got_size_bounds)
put_uint32(s->exhash, s->dh_min_size);
put_uint32(s->exhash, s->pbits);
if (s->dh_got_size_bounds)
put_uint32(s->exhash, s->dh_max_size);
put_mp_ssh2(s->exhash, s->p);
put_mp_ssh2(s->exhash, s->g);
}
put_mp_ssh2(s->exhash, s->f);
put_mp_ssh2(s->exhash, s->e);
pktout = ssh_bpp_new_pktout(s->ppl.bpp, s->kex_reply_value);
put_stringpl(pktout, s->hostkeydata);
put_mp_ssh2(pktout, s->e);
put_stringsb(pktout, finalise_and_sign_exhash(s));
pq_push(s->ppl.out_pq, pktout);
dh_cleanup(s->dh_ctx);
s->dh_ctx = NULL;
mp_free(s->f); s->f = NULL;
if (dh_is_gex(s->kex_alg)) {
mp_free(s->g); s->g = NULL;
mp_free(s->p); s->p = NULL;
}
} else if (s->kex_alg->main_type == KEXTYPE_ECDH) {
ppl_logevent("Doing ECDH key exchange with curve %s and hash %s",
ssh_ecdhkex_curve_textname(s->kex_alg),
ssh_hash_alg(s->exhash)->text_name);
s->ppl.bpp->pls->kctx = SSH2_PKTCTX_ECDHKEX;
s->ecdh_key = ssh_ecdhkex_newkey(s->kex_alg);
if (!s->ecdh_key) {
ssh_sw_abort(s->ppl.ssh, "Unable to generate key for ECDH");
*aborted = true;
return;
}
crMaybeWaitUntilV((pktin = ssh2_transport_pop(s)) != NULL);
if (pktin->type != SSH2_MSG_KEX_ECDH_INIT) {
ssh_proto_error(s->ppl.ssh, "Received unexpected packet when "
"expecting ECDH initial packet, type %d (%s)",
pktin->type,
ssh2_pkt_type(s->ppl.bpp->pls->kctx,
s->ppl.bpp->pls->actx,
pktin->type));
*aborted = true;
return;
}
{
ptrlen keydata = get_string(pktin);
put_stringpl(s->exhash, keydata);
s->K = ssh_ecdhkex_getkey(s->ecdh_key, keydata);
if (!get_err(pktin) && !s->K) {
ssh_proto_error(s->ppl.ssh, "Received invalid elliptic curve "
"point in ECDH initial packet");
*aborted = true;
return;
}
}
pktout = ssh_bpp_new_pktout(s->ppl.bpp, SSH2_MSG_KEX_ECDH_REPLY);
put_stringpl(pktout, s->hostkeydata);
{
strbuf *pubpoint = strbuf_new();
ssh_ecdhkex_getpublic(s->ecdh_key, BinarySink_UPCAST(pubpoint));
put_string(s->exhash, pubpoint->u, pubpoint->len);
put_stringsb(pktout, pubpoint);
}
put_stringsb(pktout, finalise_and_sign_exhash(s));
pq_push(s->ppl.out_pq, pktout);
ssh_ecdhkex_freekey(s->ecdh_key);
s->ecdh_key = NULL;
} else if (s->kex_alg->main_type == KEXTYPE_GSS) {
ssh_sw_abort(s->ppl.ssh, "GSS key exchange not supported in server");
} else {
assert(s->kex_alg->main_type == KEXTYPE_RSA);
ppl_logevent("Doing RSA key exchange with hash %s",
ssh_hash_alg(s->exhash)->text_name);
s->ppl.bpp->pls->kctx = SSH2_PKTCTX_RSAKEX;
const struct ssh_rsa_kex_extra *extra =
(const struct ssh_rsa_kex_extra *)s->kex_alg->extra;
if (s->ssc && s->ssc->rsa_kex_key) {
int klen = ssh_rsakex_klen(s->ssc->rsa_kex_key);
if (klen >= extra->minklen) {
ppl_logevent("Using configured %d-bit RSA key", klen);
s->rsa_kex_key = s->ssc->rsa_kex_key;
} else {
ppl_logevent("Configured %d-bit RSA key is too short (min %d)",
klen, extra->minklen);
}
}
if (!s->rsa_kex_key) {
ppl_logevent("Generating a %d-bit RSA key", extra->minklen);
s->rsa_kex_key = snew(RSAKey);
PrimeGenerationContext *pgc = primegen_new_context(
&primegen_probabilistic);
ProgressReceiver null_progress;
null_progress.vt = &null_progress_vt;
rsa_generate(s->rsa_kex_key, extra->minklen, pgc, &null_progress);
primegen_free_context(pgc);
s->rsa_kex_key->comment = NULL;
s->rsa_kex_key_needs_freeing = true;
}
pktout = ssh_bpp_new_pktout(s->ppl.bpp, SSH2_MSG_KEXRSA_PUBKEY);
put_stringpl(pktout, s->hostkeydata);
{
strbuf *pubblob = strbuf_new();
ssh_key_public_blob(&s->rsa_kex_key->sshk,
BinarySink_UPCAST(pubblob));
put_string(s->exhash, pubblob->u, pubblob->len);
put_stringsb(pktout, pubblob);
}
pq_push(s->ppl.out_pq, pktout);
crMaybeWaitUntilV((pktin = ssh2_transport_pop(s)) != NULL);
if (pktin->type != SSH2_MSG_KEXRSA_SECRET) {
ssh_proto_error(s->ppl.ssh, "Received unexpected packet when "
"expecting RSA kex secret, type %d (%s)",
pktin->type,
ssh2_pkt_type(s->ppl.bpp->pls->kctx,
s->ppl.bpp->pls->actx,
pktin->type));
*aborted = true;
return;
}
{
ptrlen encrypted_secret = get_string(pktin);
put_stringpl(s->exhash, encrypted_secret);
s->K = ssh_rsakex_decrypt(
s->rsa_kex_key, s->kex_alg->hash, encrypted_secret);
}
if (!s->K) {
ssh_proto_error(s->ppl.ssh, "Unable to decrypt RSA kex secret");
*aborted = true;
return;
}
if (s->rsa_kex_key_needs_freeing) {
ssh_rsakex_freekey(s->rsa_kex_key);
sfree(s->rsa_kex_key);
}
s->rsa_kex_key = NULL;
s->rsa_kex_key_needs_freeing = false;
pktout = ssh_bpp_new_pktout(s->ppl.bpp, SSH2_MSG_KEXRSA_DONE);
put_stringsb(pktout, finalise_and_sign_exhash(s));
pq_push(s->ppl.out_pq, pktout);
}
crFinishV;
}
Reference in New Issue View Git Blame Copy Permalink