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putty-source/ssh2kex-server.c
Simon Tatham 9285c1b93c Identify hash function implementations in the Event Log. 
Similarly to the 'AES (unaccelerated)' naming scheme I added in the
AES rewrite, the hash functions that have multiple implementations now
each come with an annotation saying which one they are.

This was more tricky for hashes than for ciphers, because the
annotation for a hash has to be a separate string literal from the
base text name, so that it can propagate into the name field for each
HMAC wrapper without looking silly.
2019-01-23 22:36:17 +00:00

301 lines
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C
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/*
* 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 "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;
}
static void no_progress(void *param, int action, int phase, int iprogress)
{
}
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);
}
s->hostkeyblob->len = 0;
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.
*/
s->p = primegen(s->pbits, 2, 2, NULL, 1, no_progress, NULL, 1);
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;
s->rsa_kex_key = snew(RSAKey);
rsa_generate(s->rsa_kex_key, extra->minklen, no_progress, NULL);
s->rsa_kex_key->comment = NULL;
}
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;
}
ssh_rsakex_freekey(s->rsa_kex_key);
s->rsa_kex_key = NULL;
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;
}
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