* Add remaining pieces of Kerberos support (closes: #275472):

  - Add GSSAPI key exchange support from
    http://www.sxw.org.uk/computing/patches/openssh.html (thanks, Stephen
    Frost).

19 files changed, 917 insertions, 18 deletions

diff --git a/Makefile.in b/Makefile.in
index 7d43562d9..947cef8c6 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -71,7 +71,7 @@ LIBSSH_OBJS=acss.o authfd.o authfile.o bufaux.o buffer.o \
         atomicio.o key.o dispatch.o kex.o mac.o uidswap.o uuencode.o misc.o \
         monitor_fdpass.o rijndael.o ssh-dss.o ssh-rsa.o dh.o kexdh.o \
         kexgex.o kexdhc.o kexgexc.o scard.o msg.o progressmeter.o dns.o \
-        entropy.o scard-opensc.o gss-genr.o
+        entropy.o scard-opensc.o gss-genr.o kexgssc.o
 
 SSHOBJS= ssh.o readconf.o clientloop.o sshtty.o \
         sshconnect.o sshconnect1.o sshconnect2.o
@@ -84,7 +84,7 @@ SSHDOBJS=sshd.o auth-rhosts.o auth-passwd.o auth-rsa.o auth-rh-rsa.o \
         auth2-none.o auth2-passwd.o auth2-pubkey.o \
         monitor_mm.o monitor.o monitor_wrap.o kexdhs.o kexgexs.o \
         auth-krb5.o \
-        auth2-gss.o gss-serv.o gss-serv-krb5.o \
+        auth2-gss.o gss-serv.o gss-serv-krb5.o kexgsss.o\
         loginrec.o auth-pam.o auth-shadow.o auth-sia.o md5crypt.o \
         audit.o audit-bsm.o
 
diff --git a/auth2-gss.c b/auth2-gss.c
index 4d468a0e8..9295d531b 100644
--- a/auth2-gss.c
+++ b/auth2-gss.c
@@ -47,6 +47,39 @@ static void input_gssapi_mic(int type, u_int32_t plen, void *ctxt);
 static void input_gssapi_exchange_complete(int type, u_int32_t plen, void *ctxt);
 static void input_gssapi_errtok(int, u_int32_t, void *);
 
+/* 
+ * The 'gssapi_keyex' userauth mechanism.
+ */
+static int
+userauth_gsskeyex(Authctxt *authctxt)
+{
+        int authenticated = 0;
+        Buffer b;
+        gss_buffer_desc mic, gssbuf;
+        u_int len;
+
+        mic.value = packet_get_string(&len);
+        mic.length = len;
+
+        packet_check_eom();
+
+        ssh_gssapi_buildmic(&b, authctxt->user, authctxt->service,
+            "gssapi-keyex");
+
+        gssbuf.value = buffer_ptr(&b);
+        gssbuf.length = buffer_len(&b);
+
+        /* gss_kex_context is NULL with privsep, so we can't check it here */
+        if (!GSS_ERROR(PRIVSEP(ssh_gssapi_checkmic(gss_kex_context, 
+            &gssbuf, &mic))))
+                authenticated = PRIVSEP(ssh_gssapi_userok(authctxt->user));
+        
+        buffer_free(&b);
+        xfree(mic.value);
+
+        return (authenticated);
+}
+
 /*
  * We only support those mechanisms that we know about (ie ones that we know
  * how to check local user kuserok and the like
@@ -285,6 +318,12 @@ input_gssapi_mic(int type, u_int32_t plen, void *ctxt)
         userauth_finish(authctxt, authenticated, "gssapi-with-mic");
 }
 
+Authmethod method_gsskeyex = {
+        "gssapi-keyx",
+        userauth_gsskeyex,
+        &options.gss_authentication
+};
+
 Authmethod method_gssapi = {
         "gssapi-with-mic",
         userauth_gssapi,
diff --git a/auth2.c b/auth2.c
index dfb284691..bb25597e7 100644
--- a/auth2.c
+++ b/auth2.c
@@ -55,6 +55,7 @@ extern Authmethod method_passwd;
 extern Authmethod method_kbdint;
 extern Authmethod method_hostbased;
 #ifdef GSSAPI
+extern Authmethod method_gsskeyex;
 extern Authmethod method_gssapi;
 #endif
 
@@ -62,6 +63,7 @@ Authmethod *authmethods[] = {
         &method_none,
         &method_pubkey,
 #ifdef GSSAPI
+        &method_gsskeyex,
         &method_gssapi,
 #endif
         &method_passwd,
diff --git a/debian/changelog b/debian/changelog
index 5859fd3de..5693ef352 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -1,6 +1,10 @@
 openssh (1:4.2p1-2) UNRELEASED; urgency=low
 
   * Annotate 1:4.1p1-1 changelog with CVE references.
+  * Add remaining pieces of Kerberos support (closes: #275472):
+    - Add GSSAPI key exchange support from
+      http://www.sxw.org.uk/computing/patches/openssh.html (thanks, Stephen
+      Frost).
 
  -- Colin Watson <cjwatson@debian.org>  Wed, 14 Sep 2005 15:48:57 +0100
 
diff --git a/gss-genr.c b/gss-genr.c
index 9bc31aa2a..743d4794f 100644
--- a/gss-genr.c
+++ b/gss-genr.c
@@ -34,12 +34,137 @@
 #include "log.h"
 #include "monitor_wrap.h"
 #include "ssh2.h"
+#include <openssl/evp.h>
 
 #include "ssh-gss.h"
 
 extern u_char *session_id2;
 extern u_int session_id2_len;
 
+typedef struct {
+        char *encoded;
+        gss_OID oid;
+} ssh_gss_kex_mapping;
+
+/*
+ * XXX - It would be nice to find a more elegant way of handling the
+ * XXX   passing of the key exchange context to the userauth routines
+ */
+
+Gssctxt *gss_kex_context = NULL;
+
+static ssh_gss_kex_mapping *gss_enc2oid = NULL;
+
+/*
+ * Return a list of the gss-group1-sha1 mechanisms supported by this program
+ *
+ * We test mechanisms to ensure that we can use them, to avoid starting
+ * a key exchange with a bad mechanism
+ */
+
+
+char *
+ssh_gssapi_client_mechanisms(char *host) {
+        gss_OID_set gss_supported;
+        OM_uint32 min_status;
+
+        gss_indicate_mechs(&min_status, &gss_supported);
+
+        return(ssh_gssapi_kex_mechs(gss_supported, ssh_gssapi_check_mechanism,
+            (void *)host));
+}
+
+char *
+ssh_gssapi_kex_mechs(gss_OID_set gss_supported, ssh_gssapi_check_fn *check,
+    void *data) {
+        Buffer buf;
+        int i, oidpos, enclen;
+        char *mechs, *encoded;
+        char digest[EVP_MAX_MD_SIZE];
+        char deroid[2];
+        const EVP_MD *evp_md = EVP_md5();
+        EVP_MD_CTX md;
+
+        evp_md = EVP_md5();
+
+        if (gss_enc2oid != NULL) {
+                for (i=0;gss_enc2oid[i].encoded!=NULL;i++)
+                        xfree(gss_enc2oid[i].encoded);
+                xfree(gss_enc2oid);
+        }
+
+        gss_enc2oid = xmalloc(sizeof(ssh_gss_kex_mapping)*
+            (gss_supported->count+1));
+
+        buffer_init(&buf);
+
+        oidpos = 0;
+        for (i=0;i<gss_supported->count;i++) {
+                if (gss_supported->elements[i].length<128 &&
+                    (*check)(&(gss_supported->elements[i]), data)) {
+
+                        deroid[0] = SSH_GSS_OIDTYPE;
+                        deroid[1] = gss_supported->elements[i].length;
+                        EVP_DigestInit(&md, evp_md);
+                        EVP_DigestUpdate(&md, deroid, 2);
+                        EVP_DigestUpdate(&md,
+                            gss_supported->elements[i].elements,
+                            gss_supported->elements[i].length);
+                        EVP_DigestFinal(&md, digest, NULL);
+
+                        encoded = xmalloc(EVP_MD_size(evp_md)*2);
+                        enclen = __b64_ntop(digest, EVP_MD_size(evp_md),
+                            encoded, EVP_MD_size(evp_md)*2);
+
+                        if (oidpos != 0)
+                            buffer_put_char(&buf,',');
+
+                        buffer_append(&buf, KEX_GSS_SHA1, 
+                            sizeof(KEX_GSS_SHA1)-1);
+                        buffer_append(&buf, encoded, enclen);
+
+                        gss_enc2oid[oidpos].oid = &(gss_supported->elements[i]);
+                        gss_enc2oid[oidpos].encoded = encoded;
+                        oidpos++;
+                }
+        }
+        gss_enc2oid[oidpos].oid = NULL;
+        gss_enc2oid[oidpos].encoded = NULL;
+
+        buffer_put_char(&buf,'\0');
+
+        mechs = xmalloc(buffer_len(&buf));
+        buffer_get(&buf, mechs, buffer_len(&buf));
+        buffer_free(&buf);
+
+        if (strlen(mechs) == 0) {
+                xfree(mechs);
+                mechs = NULL;
+        }
+        
+        return (mechs);
+}
+
+gss_OID
+ssh_gssapi_id_kex(Gssctxt *ctx, char *name) {
+        int i = 0;
+
+        if (strncmp(name, KEX_GSS_SHA1, sizeof(KEX_GSS_SHA1)-1) != 0) 
+                return NULL;
+
+        name+=sizeof(KEX_GSS_SHA1)-1; /* Skip ID string */
+
+        while (gss_enc2oid[i].encoded != NULL &&
+            strcmp(name,gss_enc2oid[i].encoded)!=0) {
+                i++;
+        }
+
+        if (gss_enc2oid[i].oid != NULL && ctx != NULL)
+                ssh_gssapi_set_oid(ctx,gss_enc2oid[i].oid);
+
+        return gss_enc2oid[i].oid;
+}
+
 /* Check that the OID in a data stream matches that in the context */
 int
 ssh_gssapi_check_oid(Gssctxt *ctx, void *data, size_t len)
@@ -250,6 +375,9 @@ ssh_gssapi_acquire_cred(Gssctxt *ctx)
 OM_uint32
 ssh_gssapi_sign(Gssctxt *ctx, gss_buffer_t buffer, gss_buffer_t hash)
 {
+        if (ctx == NULL) 
+                return -1;
+
         if ((ctx->major = gss_get_mic(&ctx->minor, ctx->context,
             GSS_C_QOP_DEFAULT, buffer, hash)))
                 ssh_gssapi_error(ctx);
@@ -257,6 +385,19 @@ ssh_gssapi_sign(Gssctxt *ctx, gss_buffer_t buffer, gss_buffer_t hash)
         return (ctx->major);
 }
 
+/* Priviledged when used by server */
+OM_uint32
+ssh_gssapi_checkmic(Gssctxt *ctx, gss_buffer_t gssbuf, gss_buffer_t gssmic)
+{
+        if (ctx == NULL)
+                return -1;
+
+        ctx->major = gss_verify_mic(&ctx->minor, ctx->context,
+            gssbuf, gssmic, NULL);
+
+        return (ctx->major);
+}
+
 void
 ssh_gssapi_buildmic(Buffer *b, const char *user, const char *service,
     const char *context)
@@ -278,4 +419,19 @@ ssh_gssapi_server_ctx(Gssctxt **ctx, gss_OID oid) {
         return (ssh_gssapi_acquire_cred(*ctx));
 }
 
+int
+ssh_gssapi_check_mechanism(gss_OID oid, void *host) {
+        Gssctxt * ctx = NULL;
+        gss_buffer_desc token;
+        OM_uint32 major, minor;
+        
+        ssh_gssapi_build_ctx(&ctx);
+        ssh_gssapi_set_oid(ctx, oid);
+        ssh_gssapi_import_name(ctx, host);
+        major = ssh_gssapi_init_ctx(ctx, 0, GSS_C_NO_BUFFER, &token, NULL);
+        gss_release_buffer(&minor, &token);
+        ssh_gssapi_delete_ctx(&ctx);
+        return (!GSS_ERROR(major));
+}
+
 #endif /* GSSAPI */
diff --git a/gss-serv.c b/gss-serv.c
index 117130459..05ae54e97 100644
--- a/gss-serv.c
+++ b/gss-serv.c
@@ -62,6 +62,28 @@ ssh_gssapi_mech* supported_mechs[]= {
 };
 
 /* Unpriviledged */
+char *
+ssh_gssapi_server_mechanisms() {
+        gss_OID_set     supported;
+
+        ssh_gssapi_supported_oids(&supported);
+        return (ssh_gssapi_kex_mechs(supported, &ssh_gssapi_server_check_mech,
+            NULL));
+}
+
+/* Unpriviledged */
+int
+ssh_gssapi_server_check_mech(gss_OID oid, void *data) {
+        Gssctxt * ctx = NULL;
+        int res;
+
+        res = !GSS_ERROR(PRIVSEP(ssh_gssapi_server_ctx(&ctx, oid)));
+        ssh_gssapi_delete_ctx(&ctx);
+
+        return (res);
+}
+
+/* Unpriviledged */
 void
 ssh_gssapi_supported_oids(gss_OID_set *oidset)
 {
@@ -298,14 +320,4 @@ ssh_gssapi_userok(char *user)
         return (0);
 }
 
-/* Priviledged */
-OM_uint32
-ssh_gssapi_checkmic(Gssctxt *ctx, gss_buffer_t gssbuf, gss_buffer_t gssmic)
-{
-        ctx->major = gss_verify_mic(&ctx->minor, ctx->context,
-            gssbuf, gssmic, NULL);
-
-        return (ctx->major);
-}
-
 #endif
diff --git a/kex.c b/kex.c
index 5dce335fe..e7147ae74 100644
--- a/kex.c
+++ b/kex.c
@@ -42,6 +42,10 @@ RCSID("$OpenBSD: kex.c,v 1.64 2005/07/25 11:59:39 markus Exp $");
 #include "dispatch.h"
 #include "monitor.h"
 
+#ifdef GSSAPI
+#include "ssh-gss.h"
+#endif
+
 #define KEX_COOKIE_LEN  16
 
 /* prototype */
@@ -298,6 +302,11 @@ choose_kex(Kex *k, char *client, char *server)
                 k->kex_type = KEX_DH_GRP14_SHA1;
         } else if (strcmp(k->name, KEX_DHGEX) == 0) {
                 k->kex_type = KEX_DH_GEX_SHA1;
+#ifdef GSSAPI
+        } else if (strncmp(k->name, KEX_GSS_SHA1, 
+            sizeof(KEX_GSS_SHA1)-1) == 0) {
+                k->kex_type = KEX_GSS_GRP1_SHA1;
+#endif
         } else
                 fatal("bad kex alg %s", k->name);
 }
diff --git a/kex.h b/kex.h
index 3024a2717..25720dff8 100644
--- a/kex.h
+++ b/kex.h
@@ -63,6 +63,7 @@ enum kex_exchange {
         KEX_DH_GRP1_SHA1,
         KEX_DH_GRP14_SHA1,
         KEX_DH_GEX_SHA1,
+        KEX_GSS_GRP1_SHA1,
         KEX_MAX
 };
 
@@ -114,6 +115,9 @@ struct Kex {
         Buffer  peer;
         int     done;
         int     flags;
+#ifdef GSSAPI
+        int     gss_deleg_creds;
+#endif
         char    *client_version_string;
         char    *server_version_string;
         int     (*verify_host_key)(Key *);
@@ -136,6 +140,11 @@ void	 kexdh_server(Kex *);
 void     kexgex_client(Kex *);
 void     kexgex_server(Kex *);
 
+#ifdef GSSAPI
+void    kexgss_client(Kex *);
+void    kexgss_server(Kex *);
+#endif
+
 u_char *
 kex_dh_hash(char *, char *, char *, int, char *, int, u_char *, int,
     BIGNUM *, BIGNUM *, BIGNUM *);
diff --git a/kexgssc.c b/kexgssc.c
new file mode 100644
index 000000000..eee96dd23
--- /dev/null
+++ b/kexgssc.c
@@ -0,0 +1,242 @@
+/*
+ * Copyright (c) 2001-2004 Simon Wilkinson. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR `AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "includes.h"
+
+#ifdef GSSAPI
+
+#include <openssl/crypto.h>
+#include <openssl/bn.h>
+
+#include "xmalloc.h"
+#include "buffer.h"
+#include "bufaux.h"
+#include "kex.h"
+#include "log.h"
+#include "packet.h"
+#include "dh.h"
+#include "canohost.h"
+#include "ssh2.h"
+#include "ssh-gss.h"
+
+void
+kexgss_client(Kex *kex) {
+        gss_buffer_desc gssbuf, send_tok, recv_tok, msg_tok, *token_ptr;
+        Gssctxt *ctxt;
+        OM_uint32 maj_status, min_status, ret_flags;
+        unsigned int klen, kout;
+        DH *dh; 
+        BIGNUM *dh_server_pub = 0;
+        BIGNUM *shared_secret = 0;      
+        unsigned char *kbuf;
+        unsigned char *hash;
+        unsigned char *serverhostkey;
+        char *msg;
+        char *lang;
+        int type = 0;
+        int first = 1;
+        int slen = 0;
+        u_int strlen;
+        
+        ssh_gssapi_build_ctx(&ctxt);
+        if (ssh_gssapi_id_kex(ctxt,kex->name) == NULL)
+                fatal("Couldn't identify host exchange");
+
+        if (ssh_gssapi_import_name(ctxt,get_canonical_hostname(1)))
+                fatal("Couldn't import hostname ");
+        
+        /* This code should match that in ssh_dh1_client */
+                
+        /* Step 1 - e is dh->pub_key */
+        dh = dh_new_group1();
+        dh_gen_key(dh, kex->we_need * 8);
+
+        /* This is f, we initialise it now to make life easier */
+        dh_server_pub = BN_new();
+        if (dh_server_pub == NULL)
+                fatal("dh_server_pub == NULL");
+
+        token_ptr = GSS_C_NO_BUFFER;
+                         
+        do {
+                debug("Calling gss_init_sec_context");
+                
+                maj_status = ssh_gssapi_init_ctx(ctxt,
+                    kex->gss_deleg_creds, token_ptr, &send_tok,
+                    &ret_flags);
+
+                if (GSS_ERROR(maj_status)) {
+                        if (send_tok.length != 0) {
+                                packet_start(SSH2_MSG_KEXGSS_CONTINUE);
+                                packet_put_string(send_tok.value,
+                                    send_tok.length);
+                        }
+                        fatal("gss_init_context failed");
+                }
+
+                /* If we've got an old receive buffer get rid of it */
+                if (token_ptr != GSS_C_NO_BUFFER)
+                        (void) gss_release_buffer(&min_status, &recv_tok);
+
+                if (maj_status == GSS_S_COMPLETE) {
+                        /* If mutual state flag is not true, kex fails */
+                        if (!(ret_flags & GSS_C_MUTUAL_FLAG))
+                                fatal("Mutual authentication failed");
+
+                        /* If integ avail flag is not true kex fails */
+                        if (!(ret_flags & GSS_C_INTEG_FLAG))
+                                fatal("Integrity check failed");
+                }
+
+                /* 
+                 * If we have data to send, then the last message that we
+                 * received cannot have been a 'complete'. 
+                 */
+                if (send_tok.length != 0) {
+                        if (first) {
+                                packet_start(SSH2_MSG_KEXGSS_INIT);
+                                packet_put_string(send_tok.value,
+                                    send_tok.length);
+                                packet_put_bignum2(dh->pub_key);
+                                first = 0;
+                        } else {
+                                packet_start(SSH2_MSG_KEXGSS_CONTINUE);
+                                packet_put_string(send_tok.value,
+                                    send_tok.length);
+                        }
+                        packet_send();
+
+                        /* If we've sent them data, they should reply */
+                
+                        type = packet_read();
+                        switch (type) {
+                        case SSH2_MSG_KEXGSS_HOSTKEY:
+                                debug("Received KEXGSS_HOSTKEY");
+                                serverhostkey = packet_get_string(&slen);
+                                break;
+                        case SSH2_MSG_KEXGSS_CONTINUE:
+                                debug("Received GSSAPI_CONTINUE");
+                                if (maj_status == GSS_S_COMPLETE) 
+                                        fatal("GSSAPI Continue received from server when complete");
+                                recv_tok.value = packet_get_string(&strlen);
+                                recv_tok.length = strlen; 
+                                break;
+                        case SSH2_MSG_KEXGSS_COMPLETE:
+                                debug("Received GSSAPI_COMPLETE");
+                                packet_get_bignum2(dh_server_pub);
+                                msg_tok.value = packet_get_string(&strlen);
+                                msg_tok.length = strlen; 
+
+                                /* Is there a token included? */
+                                if (packet_get_char()) {
+                                        recv_tok.value=
+                                            packet_get_string(&strlen);
+                                        recv_tok.length = strlen;
+                                        /* If we're already complete - protocol error */
+                                        if (maj_status == GSS_S_COMPLETE)
+                                                packet_disconnect("Protocol error: received token when complete");
+                                } else {
+                                        /* No token included */
+                                        if (maj_status != GSS_S_COMPLETE)
+                                                packet_disconnect("Protocol error: did not receive final token");
+                                }
+                                break;
+                        case SSH2_MSG_KEXGSS_ERROR:
+                                debug("Received Error");
+                                maj_status = packet_get_int();
+                                min_status = packet_get_int();
+                                msg = packet_get_string(NULL);
+                                lang = packet_get_string(NULL);
+                                fprintf(stderr,"GSSAPI Error: \n%s",msg);
+                        default:
+                                packet_disconnect("Protocol error: didn't expect packet type %d",
+                                type);
+                        }
+                        token_ptr = &recv_tok;
+                } else {
+                        /* No data, and not complete */
+                        if (maj_status != GSS_S_COMPLETE)
+                                fatal("Not complete, and no token output");
+                }
+        } while (maj_status & GSS_S_CONTINUE_NEEDED);
+
+        /* 
+         * We _must_ have received a COMPLETE message in reply from the 
+         * server, which will have set dh_server_pub and msg_tok 
+         */
+
+        if (type!=SSH2_MSG_KEXGSS_COMPLETE)
+                fatal("Didn't receive a SSH2_MSG_KEXGSS_COMPLETE when I expected it");
+
+        /* Check f in range [1, p-1] */
+        if (!dh_pub_is_valid(dh, dh_server_pub))
+                packet_disconnect("bad server public DH value");
+
+        /* compute K=f^x mod p */
+        klen = DH_size(dh);
+        kbuf = xmalloc(klen);
+        kout = DH_compute_key(kbuf, dh_server_pub, dh);
+
+        shared_secret = BN_new();
+        BN_bin2bn(kbuf,kout, shared_secret);
+        memset(kbuf, 0, klen);
+        xfree(kbuf);
+
+        /* The GSS hash is identical to the DH one */
+        hash = kex_dh_hash( kex->client_version_string, 
+            kex->server_version_string,
+            buffer_ptr(&kex->my), buffer_len(&kex->my),
+            buffer_ptr(&kex->peer), buffer_len(&kex->peer),
+            serverhostkey, slen, /* server host key */
+            dh->pub_key,        /* e */
+            dh_server_pub,      /* f */
+            shared_secret       /* K */
+        );
+        
+        gssbuf.value = hash;
+        gssbuf.length = 20;
+
+        /* Verify that the hash matches the MIC we just got. */
+        if (GSS_ERROR(ssh_gssapi_checkmic(ctxt, &gssbuf, &msg_tok)))
+                packet_disconnect("Hash's MIC didn't verify");
+        
+        DH_free(dh);
+        /* save session id */
+        if (kex->session_id == NULL) {
+                kex->session_id_len = 20;
+                kex->session_id = xmalloc(kex->session_id_len);
+                memcpy(kex->session_id, hash, kex->session_id_len);
+        }
+
+        if (gss_kex_context == NULL)
+                gss_kex_context = ctxt;
+        else
+                ssh_gssapi_delete_ctx(&ctxt);
+
+        kex_derive_keys(kex, hash, shared_secret);
+        BN_clear_free(shared_secret);
+        kex_finish(kex);
+}
+
+#endif /* GSSAPI */
diff --git a/kexgsss.c b/kexgsss.c
new file mode 100644
index 000000000..80c133ac9
--- /dev/null
+++ b/kexgsss.c
@@ -0,0 +1,204 @@
+/*
+ * Copyright (c) 2001-2004 Simon Wilkinson. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR `AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include "includes.h"
+
+#ifdef GSSAPI
+
+#include <openssl/crypto.h>
+#include <openssl/bn.h>
+
+#include "xmalloc.h"
+#include "buffer.h"
+#include "bufaux.h"
+#include "kex.h"
+#include "log.h"
+#include "packet.h"
+#include "dh.h"
+#include "ssh2.h"
+#include "ssh-gss.h"
+#include "monitor_wrap.h"
+
+void
+kexgss_server(Kex *kex)
+{
+        OM_uint32 maj_status, min_status;
+        
+        /* 
+         * Some GSSAPI implementations use the input value of ret_flags (an
+         * output variable) as a means of triggering mechanism specific 
+         * features. Initializing it to zero avoids inadvertently 
+         * activating this non-standard behaviour.
+         */
+
+        OM_uint32 ret_flags = 0;
+        gss_buffer_desc gssbuf, send_tok, recv_tok, msg_tok;
+        Gssctxt *ctxt = NULL;
+        unsigned int klen, kout;
+        unsigned char *kbuf, *hash;
+        DH *dh;
+        BIGNUM *shared_secret = NULL;
+        BIGNUM *dh_client_pub = NULL;
+        int type =0;
+        u_int slen;
+        gss_OID oid;
+        
+        /* Initialise GSSAPI */
+
+        debug2("%s: Identifying %s", __func__, kex->name);
+        oid = ssh_gssapi_id_kex(NULL, kex->name);
+        if (oid == NULL)
+           fatal("Unknown gssapi mechanism");
+
+        debug2("%s: Acquiring credentials", __func__);
+
+        if (GSS_ERROR(PRIVSEP(ssh_gssapi_server_ctx(&ctxt, oid))))
+                fatal("Unable to acquire credentials for the server");
+
+        do {
+                debug("Wait SSH2_MSG_GSSAPI_INIT");
+                type = packet_read();
+                switch(type) {
+                case SSH2_MSG_KEXGSS_INIT:
+                        if (dh_client_pub != NULL) 
+                                fatal("Received KEXGSS_INIT after initialising");
+                        recv_tok.value = packet_get_string(&slen);
+                        recv_tok.length = slen; 
+
+                        dh_client_pub = BN_new();
+
+                        if (dh_client_pub == NULL)
+                                fatal("dh_client_pub == NULL");
+                        packet_get_bignum2(dh_client_pub);
+
+                        /* Send SSH_MSG_KEXGSS_HOSTKEY here, if we want */
+                        break;
+                case SSH2_MSG_KEXGSS_CONTINUE:
+                        recv_tok.value = packet_get_string(&slen);
+                        recv_tok.length = slen; 
+                        break;
+                default:
+                        packet_disconnect(
+                            "Protocol error: didn't expect packet type %d",
+                            type);
+                }
+
+                maj_status = PRIVSEP(ssh_gssapi_accept_ctx(ctxt, &recv_tok, 
+                    &send_tok, &ret_flags));
+
+                gss_release_buffer(&min_status, &recv_tok);
+                
+                if (maj_status != GSS_S_COMPLETE && send_tok.length == 0)
+                        fatal("Zero length token output when incomplete");
+
+                if (dh_client_pub == NULL)
+                        fatal("No client public key");
+                
+                if (maj_status & GSS_S_CONTINUE_NEEDED) {
+                        debug("Sending GSSAPI_CONTINUE");
+                        packet_start(SSH2_MSG_KEXGSS_CONTINUE);
+                        packet_put_string(send_tok.value, send_tok.length);
+                        packet_send();
+                        gss_release_buffer(&min_status, &send_tok);
+                }
+        } while (maj_status & GSS_S_CONTINUE_NEEDED);
+
+        if (GSS_ERROR(maj_status)) {
+                if (send_tok.length>0) {
+                        packet_start(SSH2_MSG_KEXGSS_CONTINUE);
+                        packet_put_string(send_tok.value, send_tok.length);
+                        packet_send();
+                }
+                fatal("accept_ctx died");
+        }
+
+        if (!(ret_flags & GSS_C_MUTUAL_FLAG))
+                fatal("Mutual Authentication flag wasn't set");
+
+        if (!(ret_flags & GSS_C_INTEG_FLAG))
+                fatal("Integrity flag wasn't set");
+        
+        dh = dh_new_group1();
+        dh_gen_key(dh, kex->we_need * 8);
+
+        if (!dh_pub_is_valid(dh, dh_client_pub))
+                packet_disconnect("bad client public DH value");
+
+        klen = DH_size(dh);
+        kbuf = xmalloc(klen); 
+        kout = DH_compute_key(kbuf, dh_client_pub, dh);
+
+        shared_secret = BN_new();
+        BN_bin2bn(kbuf, kout, shared_secret);
+        memset(kbuf, 0, klen);
+        xfree(kbuf);
+
+        /* The GSSAPI hash is identical to the Diffie Helman one */
+        hash = kex_dh_hash(
+            kex->client_version_string, kex->server_version_string,
+            buffer_ptr(&kex->peer), buffer_len(&kex->peer),
+            buffer_ptr(&kex->my), buffer_len(&kex->my),
+            NULL, 0, /* Change this if we start sending host keys */
+            dh_client_pub, dh->pub_key, shared_secret
+        );
+        BN_free(dh_client_pub);
+
+        if (kex->session_id == NULL) {
+                kex->session_id_len = 20;
+                kex->session_id = xmalloc(kex->session_id_len);
+                memcpy(kex->session_id, hash, kex->session_id_len);
+        }
+
+        gssbuf.value = hash;
+        gssbuf.length = 20; /* Hashlen appears to always be 20 */
+
+        if (GSS_ERROR(PRIVSEP(ssh_gssapi_sign(ctxt,&gssbuf,&msg_tok))))
+                fatal("Couldn't get MIC");
+
+        packet_start(SSH2_MSG_KEXGSS_COMPLETE);
+        packet_put_bignum2(dh->pub_key);
+        packet_put_string((char *)msg_tok.value,msg_tok.length);
+
+        if (send_tok.length!=0) {
+                packet_put_char(1); /* true */
+                packet_put_string((char *)send_tok.value, send_tok.length);
+        } else {
+                packet_put_char(0); /* false */
+        }
+        packet_send();
+
+        gss_release_buffer(&min_status, &send_tok);     
+
+        if (gss_kex_context == NULL)
+                gss_kex_context = ctxt;
+        else 
+                ssh_gssapi_delete_ctx(&ctxt);
+
+        DH_free(dh);
+
+        kex_derive_keys(kex, hash, shared_secret);
+        BN_clear_free(shared_secret);
+        kex_finish(kex);
+}
+#endif /* GSSAPI */
diff --git a/key.c b/key.c
index 08c158b59..239a35919 100644
--- a/key.c
+++ b/key.c
@@ -650,6 +650,8 @@ key_type_from_name(char *name)
                 return KEY_RSA;
         } else if (strcmp(name, "ssh-dss") == 0) {
                 return KEY_DSA;
+        } else if (strcmp(name, "null") == 0) {
+                return KEY_NULL;
         }
         debug2("key_type_from_name: unknown key type '%s'", name);
         return KEY_UNSPEC;
diff --git a/key.h b/key.h
index 50df8500b..6358e955f 100644
--- a/key.h
+++ b/key.h
@@ -34,6 +34,7 @@ enum types {
         KEY_RSA1,
         KEY_RSA,
         KEY_DSA,
+        KEY_NULL,
         KEY_UNSPEC
 };
 enum fp_type {
diff --git a/monitor.c b/monitor.c
index 081aabbdc..0d100ab56 100644
--- a/monitor.c
+++ b/monitor.c
@@ -141,6 +141,7 @@ int mm_answer_gss_setup_ctx(int, Buffer *);
 int mm_answer_gss_accept_ctx(int, Buffer *);
 int mm_answer_gss_userok(int, Buffer *);
 int mm_answer_gss_checkmic(int, Buffer *);
+int mm_answer_gss_sign(int, Buffer *);
 #endif
 
 #ifdef SSH_AUDIT_EVENTS
@@ -209,11 +210,17 @@ struct mon_table mon_dispatch_proto20[] = {
     {MONITOR_REQ_GSSSTEP, MON_ISAUTH, mm_answer_gss_accept_ctx},
     {MONITOR_REQ_GSSUSEROK, MON_AUTH, mm_answer_gss_userok},
     {MONITOR_REQ_GSSCHECKMIC, MON_ISAUTH, mm_answer_gss_checkmic},
+    {MONITOR_REQ_GSSSIGN, MON_ONCE, mm_answer_gss_sign},
 #endif
     {0, 0, NULL}
 };
 
 struct mon_table mon_dispatch_postauth20[] = {
+#ifdef GSSAPI
+    {MONITOR_REQ_GSSSETUP, 0, mm_answer_gss_setup_ctx},
+    {MONITOR_REQ_GSSSTEP, 0, mm_answer_gss_accept_ctx},
+    {MONITOR_REQ_GSSSIGN, 0, mm_answer_gss_sign},
+#endif
     {MONITOR_REQ_MODULI, 0, mm_answer_moduli},
     {MONITOR_REQ_SIGN, 0, mm_answer_sign},
     {MONITOR_REQ_PTY, 0, mm_answer_pty},
@@ -318,6 +325,10 @@ monitor_child_preauth(Authctxt *_authctxt, struct monitor *pmonitor)
                 /* Permit requests for moduli and signatures */
                 monitor_permit(mon_dispatch, MONITOR_REQ_MODULI, 1);
                 monitor_permit(mon_dispatch, MONITOR_REQ_SIGN, 1);
+#ifdef GSSAPI
+                /* and for the GSSAPI key exchange */
+                monitor_permit(mon_dispatch, MONITOR_REQ_GSSSETUP, 1);
+#endif
         } else {
                 mon_dispatch = mon_dispatch_proto15;
 
@@ -391,6 +402,10 @@ monitor_child_postauth(struct monitor *pmonitor)
                 monitor_permit(mon_dispatch, MONITOR_REQ_MODULI, 1);
                 monitor_permit(mon_dispatch, MONITOR_REQ_SIGN, 1);
                 monitor_permit(mon_dispatch, MONITOR_REQ_TERM, 1);
+#ifdef GSSAPI
+                /* and for the GSSAPI key exchange */
+                monitor_permit(mon_dispatch, MONITOR_REQ_GSSSETUP, 1);
+#endif          
         } else {
                 mon_dispatch = mon_dispatch_postauth15;
                 monitor_permit(mon_dispatch, MONITOR_REQ_TERM, 1);
@@ -1629,6 +1644,9 @@ mm_get_kex(Buffer *m)
         kex->kex[KEX_DH_GRP1_SHA1] = kexdh_server;
         kex->kex[KEX_DH_GRP14_SHA1] = kexdh_server;
         kex->kex[KEX_DH_GEX_SHA1] = kexgex_server;
+#ifdef GSSAPI
+        kex->kex[KEX_GSS_GRP1_SHA1] = kexgss_server;
+#endif
         kex->server = 1;
         kex->hostkey_type = buffer_get_int(m);
         kex->kex_type = buffer_get_int(m);
@@ -1871,6 +1889,7 @@ mm_answer_gss_accept_ctx(int sock, Buffer *m)
                 monitor_permit(mon_dispatch, MONITOR_REQ_GSSSTEP, 0);
                 monitor_permit(mon_dispatch, MONITOR_REQ_GSSUSEROK, 1);
                 monitor_permit(mon_dispatch, MONITOR_REQ_GSSCHECKMIC, 1);
+                monitor_permit(mon_dispatch, MONITOR_REQ_GSSSIGN, 1);
         }
         return (0);
 }
@@ -1921,4 +1940,39 @@ mm_answer_gss_userok(int sock, Buffer *m)
         /* Monitor loop will terminate if authenticated */
         return (authenticated);
 }
+
+int 
+mm_answer_gss_sign(int socket, Buffer *m)
+{
+        gss_buffer_desc data, hash;
+        OM_uint32 major, minor;
+
+        data.value = buffer_get_string(m, &data.length);
+        if (data.length != 20) 
+                fatal("%s: data length incorrect: %d", __func__, data.length);
+
+        /* Save the session ID on the first time around */
+        if (session_id2_len == 0) {
+                session_id2_len = data.length;
+                session_id2 = xmalloc(session_id2_len);
+                memcpy(session_id2, data.value, session_id2_len);
+        }
+        major = ssh_gssapi_sign(gsscontext, &data, &hash);
+
+        xfree(data.value);
+
+        buffer_clear(m);
+        buffer_put_int(m, major);
+        buffer_put_string(m, hash.value, hash.length);
+
+        mm_request_send(socket, MONITOR_ANS_GSSSIGN, m);
+
+        gss_release_buffer(&minor, &hash);
+
+        /* Turn on getpwnam permissions */
+        monitor_permit(mon_dispatch, MONITOR_REQ_PWNAM, 1);
+
+        return (0);
+}
+
 #endif /* GSSAPI */
diff --git a/monitor.h b/monitor.h
index 13ce3e1ca..7b306b4af 100644
--- a/monitor.h
+++ b/monitor.h
@@ -53,6 +53,7 @@ enum monitor_reqtype {
         MONITOR_REQ_GSSSTEP, MONITOR_ANS_GSSSTEP,
         MONITOR_REQ_GSSUSEROK, MONITOR_ANS_GSSUSEROK,
         MONITOR_REQ_GSSCHECKMIC, MONITOR_ANS_GSSCHECKMIC,
+        MONITOR_REQ_GSSSIGN, MONITOR_ANS_GSSSIGN,
         MONITOR_REQ_PAM_START,
         MONITOR_REQ_PAM_ACCOUNT, MONITOR_ANS_PAM_ACCOUNT,
         MONITOR_REQ_PAM_INIT_CTX, MONITOR_ANS_PAM_INIT_CTX,
diff --git a/monitor_wrap.c b/monitor_wrap.c
index d8814682a..63d158b67 100644
--- a/monitor_wrap.c
+++ b/monitor_wrap.c
@@ -1217,4 +1217,25 @@ mm_ssh_gssapi_userok(char *user)
         debug3("%s: user %sauthenticated",__func__, authenticated ? "" : "not ");
         return (authenticated);
 }
+
+OM_uint32
+mm_ssh_gssapi_sign(Gssctxt *ctx, gss_buffer_desc *data, gss_buffer_desc *hash)
+{
+        Buffer m;
+        OM_uint32 major;
+
+        buffer_init(&m);
+        buffer_put_string(&m, data->value, data->length);
+
+        mm_request_send(pmonitor->m_recvfd, MONITOR_REQ_GSSSIGN, &m);
+        mm_request_receive_expect(pmonitor->m_recvfd, MONITOR_ANS_GSSSIGN, &m);
+
+        major = buffer_get_int(&m);
+        hash->value = buffer_get_string(&m, &hash->length);
+
+        buffer_free(&m);
+
+        return(major);
+}
+
 #endif /* GSSAPI */
diff --git a/monitor_wrap.h b/monitor_wrap.h
index 5e8d4bf5a..c52f6e153 100644
--- a/monitor_wrap.h
+++ b/monitor_wrap.h
@@ -63,6 +63,7 @@ OM_uint32 mm_ssh_gssapi_accept_ctx(Gssctxt *,
    gss_buffer_desc *, gss_buffer_desc *, OM_uint32 *);
 int mm_ssh_gssapi_userok(char *user);
 OM_uint32 mm_ssh_gssapi_checkmic(Gssctxt *, gss_buffer_t, gss_buffer_t);
+OM_uint32 mm_ssh_gssapi_sign(Gssctxt *, gss_buffer_t, gss_buffer_t);
 #endif
 
 #ifdef USE_PAM
diff --git a/ssh-gss.h b/ssh-gss.h
index 52fb49a6f..74ce6f8bc 100644
--- a/ssh-gss.h
+++ b/ssh-gss.h
@@ -62,6 +62,13 @@
 
 #define SSH_GSS_OIDTYPE 0x06
 
+#define SSH2_MSG_KEXGSS_INIT                           30
+#define SSH2_MSG_KEXGSS_CONTINUE                       31
+#define SSH2_MSG_KEXGSS_COMPLETE                       32
+#define SSH2_MSG_KEXGSS_HOSTKEY                                33
+#define SSH2_MSG_KEXGSS_ERROR                          34
+#define KEX_GSS_SHA1                                   "gss-group1-sha1-"
+
 typedef struct {
         char *filename;
         char *envvar;
@@ -99,6 +106,7 @@ typedef struct {
 } Gssctxt;
 
 extern ssh_gssapi_mech *supported_mechs[];
+extern Gssctxt *gss_kex_context;
 
 int  ssh_gssapi_check_oid(Gssctxt *, void *, size_t);
 void ssh_gssapi_set_oid_data(Gssctxt *, void *, size_t);
@@ -121,7 +129,13 @@ OM_uint32 ssh_gssapi_sign(Gssctxt *, gss_buffer_t, gss_buffer_t);
 OM_uint32 ssh_gssapi_server_ctx(Gssctxt **, gss_OID);
 void ssh_gssapi_buildmic(Buffer *, const char *, const char *, const char *);
 
-/* In the server */
+typedef int ssh_gssapi_check_fn(gss_OID, void *);
+char *ssh_gssapi_client_mechanisms(char *host);
+char *ssh_gssapi_kex_mechs(gss_OID_set, ssh_gssapi_check_fn *, void *);
+int ssh_gssapi_check_mechanism(gss_OID, void *);
+gss_OID ssh_gssapi_id_kex(Gssctxt *, char *);
+
+int ssh_gssapi_server_check_mech(gss_OID, void *);
 int ssh_gssapi_userok(char *name);
 OM_uint32 ssh_gssapi_checkmic(Gssctxt *, gss_buffer_t, gss_buffer_t);
 void ssh_gssapi_do_child(char ***, u_int *);
diff --git a/sshconnect2.c b/sshconnect2.c
index ee7932d68..e40786f87 100644
--- a/sshconnect2.c
+++ b/sshconnect2.c
@@ -84,9 +84,26 @@ ssh_kex2(char *host, struct sockaddr *hostaddr)
 {
         Kex *kex;
 
+#ifdef GSSAPI
+        char *orig, *gss;
+        int len;
+#endif
+
         xxx_host = host;
         xxx_hostaddr = hostaddr;
 
+#ifdef GSSAPI
+        orig = myproposal[PROPOSAL_KEX_ALGS];
+        gss = ssh_gssapi_client_mechanisms(get_canonical_hostname(1));
+        debug("Offering GSSAPI proposal: %s",gss);
+        if (gss) {
+                len = strlen(orig) + strlen(gss) + 2;
+                myproposal[PROPOSAL_KEX_ALGS] = xmalloc(len);
+                snprintf(myproposal[PROPOSAL_KEX_ALGS], len, "%s,%s", gss, 
+                    orig);
+        }
+#endif
+
         if (options.ciphers == (char *)-1) {
                 logit("No valid ciphers for protocol version 2 given, using defaults.");
                 options.ciphers = NULL;
@@ -114,6 +131,16 @@ ssh_kex2(char *host, struct sockaddr *hostaddr)
                 myproposal[PROPOSAL_SERVER_HOST_KEY_ALGS] =
                     options.hostkeyalgorithms;
 
+#ifdef GSSAPI
+        if (gss) {
+                orig = myproposal[PROPOSAL_SERVER_HOST_KEY_ALGS];
+                len = strlen(orig) + sizeof(",null");
+                myproposal[PROPOSAL_SERVER_HOST_KEY_ALGS] = xmalloc(len);
+                snprintf(myproposal[PROPOSAL_SERVER_HOST_KEY_ALGS], len, 
+                    "%s,null", orig);
+        }
+#endif
+
         if (options.rekey_limit)
                 packet_set_rekey_limit(options.rekey_limit);
 
@@ -122,10 +149,17 @@ ssh_kex2(char *host, struct sockaddr *hostaddr)
         kex->kex[KEX_DH_GRP1_SHA1] = kexdh_client;
         kex->kex[KEX_DH_GRP14_SHA1] = kexdh_client;
         kex->kex[KEX_DH_GEX_SHA1] = kexgex_client;
+#ifdef GSSAPI
+        kex->kex[KEX_GSS_GRP1_SHA1] = kexgss_client;
+#endif
         kex->client_version_string=client_version_string;
         kex->server_version_string=server_version_string;
         kex->verify_host_key=&verify_host_key_callback;
 
+#ifdef GSSAPI
+        kex->gss_deleg_creds = options.gss_deleg_creds;
+#endif
+
         xxx_kex = kex;
 
         dispatch_run(DISPATCH_BLOCK, &kex->done, kex);
@@ -208,6 +242,7 @@ void	input_gssapi_token(int type, u_int32_t, void *);
 void    input_gssapi_hash(int type, u_int32_t, void *);
 void    input_gssapi_error(int, u_int32_t, void *);
 void    input_gssapi_errtok(int, u_int32_t, void *);
+int     userauth_gsskeyx(Authctxt *authctxt);
 #endif
 
 void    userauth(Authctxt *, char *);
@@ -223,6 +258,10 @@ static char *authmethods_get(void);
 
 Authmethod authmethods[] = {
 #ifdef GSSAPI
+        {"gssapi-keyx",
+                userauth_gsskeyx,
+                &options.gss_authentication,
+                NULL},
         {"gssapi-with-mic",
                 userauth_gssapi,
                 &options.gss_authentication,
@@ -706,6 +745,47 @@ input_gssapi_error(int type, u_int32_t plen, void *ctxt)
         xfree(msg);
         xfree(lang);
 }
+
+int
+userauth_gsskeyx(Authctxt *authctxt)
+{
+        Buffer b;
+        gss_buffer_desc gssbuf, mic;
+        OM_uint32 ms;
+
+        static int attempt = 0;
+        if (attempt++ >= 1)
+                return (0);
+
+        if (gss_kex_context == NULL) {
+                debug("No valid Key exchange context"); 
+                return (0);
+        }
+
+        ssh_gssapi_buildmic(&b, authctxt->server_user, authctxt->service,
+            "gssapi-keyex");
+
+        gssbuf.value = buffer_ptr(&b);
+        gssbuf.length = buffer_len(&b);
+
+        if (GSS_ERROR(ssh_gssapi_sign(gss_kex_context, &gssbuf, &mic))) {
+                buffer_free(&b);
+                return (0);
+        }
+
+        packet_start(SSH2_MSG_USERAUTH_REQUEST);
+        packet_put_cstring(authctxt->server_user);
+        packet_put_cstring(authctxt->service);
+        packet_put_cstring(authctxt->method->name);
+        packet_put_string(mic.value, mic.length);
+        packet_send();
+
+        buffer_free(&b);
+        gss_release_buffer(&ms, &mic);
+
+        return (1);
+}
+
 #endif /* GSSAPI */
 
 int
diff --git a/sshd.c b/sshd.c
index 86468318e..967f5e7f0 100644
--- a/sshd.c
+++ b/sshd.c
@@ -1122,10 +1122,12 @@ main(int ac, char **av)
                 logit("Disabling protocol version 1. Could not load host key");
                 options.protocol &= ~SSH_PROTO_1;
         }
+#ifndef GSSAPI
         if ((options.protocol & SSH_PROTO_2) && !sensitive_data.have_ssh2_key) {
                 logit("Disabling protocol version 2. Could not load host key");
                 options.protocol &= ~SSH_PROTO_2;
         }
+#endif
         if (!(options.protocol & (SSH_PROTO_1|SSH_PROTO_2))) {
                 logit("sshd: no hostkeys available -- exiting.");
                 exit(1);
@@ -2011,13 +2013,59 @@ do_ssh2_kex(void)
         myproposal[PROPOSAL_SERVER_HOST_KEY_ALGS] = list_hostkey_types();
 
         /* start key exchange */
-        kex = kex_setup(myproposal);
-        kex->kex[KEX_DH_GRP1_SHA1] = kexdh_server;
+  
+#ifdef GSSAPI
+        {
+        char *orig;
+        char *gss = NULL;
+        char *newstr = NULL;
+        orig = myproposal[PROPOSAL_KEX_ALGS];
+
+        /* 
+         * If we don't have a host key, then there's no point advertising
+         * the other key exchange algorithms
+         */
+
+        if (strlen(myproposal[PROPOSAL_SERVER_HOST_KEY_ALGS]) == 0)
+                orig = NULL;
+
+        gss = ssh_gssapi_server_mechanisms();
+
+        if (gss && orig) {
+                int len = strlen(orig) + strlen(gss) + 2;
+                newstr = xmalloc(len);
+                snprintf(newstr, len, "%s,%s", gss, orig);
+        } else if (gss) {
+                newstr = gss;
+        } else if (orig) {
+                newstr = orig;
+        }
+        /* 
+         * If we've got GSSAPI mechanisms, then we've got the 'null' host
+         * key alg, but we can't tell people about it unless its the only
+         * host key algorithm we support
+         */
+        if (gss && (strlen(myproposal[PROPOSAL_SERVER_HOST_KEY_ALGS])) == 0)
+                myproposal[PROPOSAL_SERVER_HOST_KEY_ALGS] = "null";
+
+        if (newstr)
+                myproposal[PROPOSAL_KEX_ALGS] = newstr;
+        else
+                fatal("No supported key exchange algorithms");
+        }
+#endif
+
+        /* start key exchange */
+        kex = kex_setup(myproposal);
+        kex->kex[KEX_DH_GRP1_SHA1] = kexdh_server;
         kex->kex[KEX_DH_GRP14_SHA1] = kexdh_server;
         kex->kex[KEX_DH_GEX_SHA1] = kexgex_server;
-        kex->server = 1;
-        kex->client_version_string=client_version_string;
-        kex->server_version_string=server_version_string;
+#ifdef GSSAPI
+        kex->kex[KEX_GSS_GRP1_SHA1] = kexgss_server;
+#endif
+        kex->server = 1;
+        kex->client_version_string=client_version_string;
+        kex->server_version_string=server_version_string;
         kex->load_host_key=&get_hostkey_by_type;
         kex->host_key_index=&get_hostkey_index;