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https://git.tartarus.org/simon/putty.git
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e103ab1fb6
Until now, every kex method has represented the output as an mp_int. So we were storing it in the mp_int field s->K, and adding it to the exchange hash and key derivation hashes via put_mp_ssh2. But there's now going to be the first kex method that represents the output as a string (so that it might have the top bit set, or multiple leading zero bytes, without its length varying). So we now need to be more general. The most general thing it's sensible to do is to replace s->K with a strbuf containing _already-encoded_ data to become part of the hash, including length fields if necessary. So every existing kex method still derives an mp_int, but then immediately puts it into that strbuf using put_mp_ssh2 and frees it.
339 lines
12 KiB
C
339 lines
12 KiB
C
/*
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* Server side of key exchange for the SSH-2 transport protocol (RFC 4253).
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*/
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#include <assert.h>
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#include "putty.h"
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#include "ssh.h"
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#include "bpp.h"
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#include "ppl.h"
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#include "sshcr.h"
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#include "server.h"
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#include "sshkeygen.h"
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#include "storage.h"
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#include "transport2.h"
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#include "mpint.h"
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void ssh2_transport_provide_hostkeys(PacketProtocolLayer *ppl,
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ssh_key *const *hostkeys, int nhostkeys)
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{
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struct ssh2_transport_state *s =
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container_of(ppl, struct ssh2_transport_state, ppl);
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s->hostkeys = hostkeys;
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s->nhostkeys = nhostkeys;
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}
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static strbuf *finalise_and_sign_exhash(struct ssh2_transport_state *s)
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{
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strbuf *sb;
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ssh2transport_finalise_exhash(s);
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sb = strbuf_new();
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ssh_key_sign(
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s->hkey, make_ptrlen(s->exchange_hash, s->kex_alg->hash->hlen),
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s->hkflags, BinarySink_UPCAST(sb));
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return sb;
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}
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void ssh2kex_coroutine(struct ssh2_transport_state *s, bool *aborted)
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{
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PacketProtocolLayer *ppl = &s->ppl; /* for ppl_logevent */
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PktIn *pktin;
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PktOut *pktout;
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crBegin(s->crStateKex);
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{
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int i;
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for (i = 0; i < s->nhostkeys; i++)
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if (ssh_key_alg(s->hostkeys[i]) == s->hostkey_alg) {
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s->hkey = s->hostkeys[i];
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break;
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}
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assert(s->hkey);
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}
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strbuf_clear(s->hostkeyblob);
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ssh_key_public_blob(s->hkey, BinarySink_UPCAST(s->hostkeyblob));
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s->hostkeydata = ptrlen_from_strbuf(s->hostkeyblob);
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put_stringpl(s->exhash, s->hostkeydata);
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if (s->kex_alg->main_type == KEXTYPE_DH) {
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/*
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* If we're doing Diffie-Hellman group exchange, start by
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* waiting for the group request.
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*/
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if (dh_is_gex(s->kex_alg)) {
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ppl_logevent("Doing Diffie-Hellman group exchange");
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s->ppl.bpp->pls->kctx = SSH2_PKTCTX_DHGEX;
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crMaybeWaitUntilV((pktin = ssh2_transport_pop(s)) != NULL);
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if (pktin->type != SSH2_MSG_KEX_DH_GEX_REQUEST &&
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pktin->type != SSH2_MSG_KEX_DH_GEX_REQUEST_OLD) {
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ssh_proto_error(s->ppl.ssh, "Received unexpected packet when "
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"expecting Diffie-Hellman group exchange "
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"request, type %d (%s)", pktin->type,
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ssh2_pkt_type(s->ppl.bpp->pls->kctx,
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s->ppl.bpp->pls->actx,
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pktin->type));
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*aborted = true;
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return;
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}
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if (pktin->type != SSH2_MSG_KEX_DH_GEX_REQUEST_OLD) {
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s->dh_got_size_bounds = true;
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s->dh_min_size = get_uint32(pktin);
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s->pbits = get_uint32(pktin);
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s->dh_max_size = get_uint32(pktin);
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} else {
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s->dh_got_size_bounds = false;
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s->pbits = get_uint32(pktin);
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}
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/*
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* This is a hopeless strategy for making a secure DH
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* group! It's good enough for testing a client against,
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* but not for serious use.
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*/
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PrimeGenerationContext *pgc = primegen_new_context(
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&primegen_probabilistic);
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ProgressReceiver null_progress;
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null_progress.vt = &null_progress_vt;
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s->p = primegen_generate(pgc, pcs_new(s->pbits), &null_progress);
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primegen_free_context(pgc);
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s->g = mp_from_integer(2);
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s->dh_ctx = dh_setup_gex(s->p, s->g);
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s->kex_init_value = SSH2_MSG_KEX_DH_GEX_INIT;
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s->kex_reply_value = SSH2_MSG_KEX_DH_GEX_REPLY;
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pktout = ssh_bpp_new_pktout(s->ppl.bpp, SSH2_MSG_KEX_DH_GEX_GROUP);
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put_mp_ssh2(pktout, s->p);
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put_mp_ssh2(pktout, s->g);
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pq_push(s->ppl.out_pq, pktout);
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} else {
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s->ppl.bpp->pls->kctx = SSH2_PKTCTX_DHGROUP;
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s->dh_ctx = dh_setup_group(s->kex_alg);
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s->kex_init_value = SSH2_MSG_KEXDH_INIT;
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s->kex_reply_value = SSH2_MSG_KEXDH_REPLY;
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ppl_logevent("Using Diffie-Hellman with standard group \"%s\"",
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s->kex_alg->groupname);
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}
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ppl_logevent("Doing Diffie-Hellman key exchange with hash %s",
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ssh_hash_alg(s->exhash)->text_name);
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/*
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* Generate e for Diffie-Hellman.
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*/
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s->e = dh_create_e(s->dh_ctx);
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/*
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* Wait to receive f.
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*/
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crMaybeWaitUntilV((pktin = ssh2_transport_pop(s)) != NULL);
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if (pktin->type != s->kex_init_value) {
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ssh_proto_error(s->ppl.ssh, "Received unexpected packet when "
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"expecting Diffie-Hellman initial packet, "
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"type %d (%s)", pktin->type,
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ssh2_pkt_type(s->ppl.bpp->pls->kctx,
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s->ppl.bpp->pls->actx,
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pktin->type));
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*aborted = true;
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return;
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}
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s->f = get_mp_ssh2(pktin);
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if (get_err(pktin)) {
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ssh_proto_error(s->ppl.ssh,
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"Unable to parse Diffie-Hellman initial packet");
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*aborted = true;
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return;
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}
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{
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const char *err = dh_validate_f(s->dh_ctx, s->f);
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if (err) {
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ssh_proto_error(s->ppl.ssh, "Diffie-Hellman initial packet "
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"failed validation: %s", err);
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*aborted = true;
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return;
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}
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}
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mp_int *K = dh_find_K(s->dh_ctx, s->f);
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put_mp_ssh2(s->kex_shared_secret, K);
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mp_free(K);
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if (dh_is_gex(s->kex_alg)) {
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if (s->dh_got_size_bounds)
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put_uint32(s->exhash, s->dh_min_size);
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put_uint32(s->exhash, s->pbits);
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if (s->dh_got_size_bounds)
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put_uint32(s->exhash, s->dh_max_size);
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put_mp_ssh2(s->exhash, s->p);
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put_mp_ssh2(s->exhash, s->g);
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}
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put_mp_ssh2(s->exhash, s->f);
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put_mp_ssh2(s->exhash, s->e);
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pktout = ssh_bpp_new_pktout(s->ppl.bpp, s->kex_reply_value);
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put_stringpl(pktout, s->hostkeydata);
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put_mp_ssh2(pktout, s->e);
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put_stringsb(pktout, finalise_and_sign_exhash(s));
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pq_push(s->ppl.out_pq, pktout);
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dh_cleanup(s->dh_ctx);
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s->dh_ctx = NULL;
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mp_free(s->f); s->f = NULL;
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if (dh_is_gex(s->kex_alg)) {
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mp_free(s->g); s->g = NULL;
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mp_free(s->p); s->p = NULL;
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}
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} else if (s->kex_alg->main_type == KEXTYPE_ECDH) {
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ppl_logevent("Doing ECDH key exchange with curve %s and hash %s",
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ssh_ecdhkex_curve_textname(s->kex_alg),
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ssh_hash_alg(s->exhash)->text_name);
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s->ppl.bpp->pls->kctx = SSH2_PKTCTX_ECDHKEX;
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s->ecdh_key = ssh_ecdhkex_newkey(s->kex_alg);
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if (!s->ecdh_key) {
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ssh_sw_abort(s->ppl.ssh, "Unable to generate key for ECDH");
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*aborted = true;
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return;
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}
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crMaybeWaitUntilV((pktin = ssh2_transport_pop(s)) != NULL);
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if (pktin->type != SSH2_MSG_KEX_ECDH_INIT) {
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ssh_proto_error(s->ppl.ssh, "Received unexpected packet when "
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"expecting ECDH initial packet, type %d (%s)",
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pktin->type,
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ssh2_pkt_type(s->ppl.bpp->pls->kctx,
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s->ppl.bpp->pls->actx,
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pktin->type));
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*aborted = true;
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return;
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}
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{
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ptrlen keydata = get_string(pktin);
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put_stringpl(s->exhash, keydata);
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mp_int *K = ssh_ecdhkex_getkey(s->ecdh_key, keydata);
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if (!get_err(pktin) && !K) {
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ssh_proto_error(s->ppl.ssh, "Received invalid elliptic curve "
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"point in ECDH initial packet");
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*aborted = true;
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return;
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}
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put_mp_ssh2(s->kex_shared_secret, K);
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mp_free(K);
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}
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pktout = ssh_bpp_new_pktout(s->ppl.bpp, SSH2_MSG_KEX_ECDH_REPLY);
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put_stringpl(pktout, s->hostkeydata);
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{
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strbuf *pubpoint = strbuf_new();
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ssh_ecdhkex_getpublic(s->ecdh_key, BinarySink_UPCAST(pubpoint));
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put_string(s->exhash, pubpoint->u, pubpoint->len);
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put_stringsb(pktout, pubpoint);
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}
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put_stringsb(pktout, finalise_and_sign_exhash(s));
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pq_push(s->ppl.out_pq, pktout);
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ssh_ecdhkex_freekey(s->ecdh_key);
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s->ecdh_key = NULL;
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} else if (s->kex_alg->main_type == KEXTYPE_GSS) {
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ssh_sw_abort(s->ppl.ssh, "GSS key exchange not supported in server");
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} else {
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assert(s->kex_alg->main_type == KEXTYPE_RSA);
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ppl_logevent("Doing RSA key exchange with hash %s",
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ssh_hash_alg(s->exhash)->text_name);
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s->ppl.bpp->pls->kctx = SSH2_PKTCTX_RSAKEX;
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const struct ssh_rsa_kex_extra *extra =
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(const struct ssh_rsa_kex_extra *)s->kex_alg->extra;
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if (s->ssc && s->ssc->rsa_kex_key) {
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int klen = ssh_rsakex_klen(s->ssc->rsa_kex_key);
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if (klen >= extra->minklen) {
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ppl_logevent("Using configured %d-bit RSA key", klen);
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s->rsa_kex_key = s->ssc->rsa_kex_key;
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} else {
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ppl_logevent("Configured %d-bit RSA key is too short (min %d)",
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klen, extra->minklen);
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}
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}
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if (!s->rsa_kex_key) {
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ppl_logevent("Generating a %d-bit RSA key", extra->minklen);
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s->rsa_kex_key = snew(RSAKey);
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PrimeGenerationContext *pgc = primegen_new_context(
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&primegen_probabilistic);
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ProgressReceiver null_progress;
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null_progress.vt = &null_progress_vt;
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rsa_generate(s->rsa_kex_key, extra->minklen, false,
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pgc, &null_progress);
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primegen_free_context(pgc);
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s->rsa_kex_key->comment = NULL;
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s->rsa_kex_key_needs_freeing = true;
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}
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pktout = ssh_bpp_new_pktout(s->ppl.bpp, SSH2_MSG_KEXRSA_PUBKEY);
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put_stringpl(pktout, s->hostkeydata);
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{
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strbuf *pubblob = strbuf_new();
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ssh_key_public_blob(&s->rsa_kex_key->sshk,
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BinarySink_UPCAST(pubblob));
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put_string(s->exhash, pubblob->u, pubblob->len);
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put_stringsb(pktout, pubblob);
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}
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pq_push(s->ppl.out_pq, pktout);
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crMaybeWaitUntilV((pktin = ssh2_transport_pop(s)) != NULL);
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if (pktin->type != SSH2_MSG_KEXRSA_SECRET) {
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ssh_proto_error(s->ppl.ssh, "Received unexpected packet when "
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"expecting RSA kex secret, type %d (%s)",
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pktin->type,
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ssh2_pkt_type(s->ppl.bpp->pls->kctx,
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s->ppl.bpp->pls->actx,
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pktin->type));
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*aborted = true;
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return;
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}
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mp_int *K;
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{
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ptrlen encrypted_secret = get_string(pktin);
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put_stringpl(s->exhash, encrypted_secret);
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K = ssh_rsakex_decrypt(
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s->rsa_kex_key, s->kex_alg->hash, encrypted_secret);
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}
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if (!K) {
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ssh_proto_error(s->ppl.ssh, "Unable to decrypt RSA kex secret");
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*aborted = true;
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return;
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}
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put_mp_ssh2(s->kex_shared_secret, K);
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mp_free(K);
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if (s->rsa_kex_key_needs_freeing) {
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ssh_rsakex_freekey(s->rsa_kex_key);
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sfree(s->rsa_kex_key);
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}
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s->rsa_kex_key = NULL;
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s->rsa_kex_key_needs_freeing = false;
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pktout = ssh_bpp_new_pktout(s->ppl.bpp, SSH2_MSG_KEXRSA_DONE);
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put_stringsb(pktout, finalise_and_sign_exhash(s));
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pq_push(s->ppl.out_pq, pktout);
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}
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crFinishV;
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}
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