kex: implement curve25519-sha256@libssh.org

2025-08-08 19:02:06 +03:00 · 2013-09-21 23:34:50 +02:00
parent 391bd88355
commit 666db37e21
9 changed files with 404 additions and 6 deletions
--- a/include/libssh/crypto.h
+++ b/include/libssh/crypto.h
@@ -44,6 +44,7 @@
 #endif
 #include "libssh/ecdh.h"
 #include "libssh/kex.h"
+#include "libssh/curve25519.h"

 enum ssh_key_exchange_e {
  /* diffie-hellman-group1-sha1 */
@@ -51,7 +52,9 @@ enum ssh_key_exchange_e {
  /* diffie-hellman-group14-sha1 */
  SSH_KEX_DH_GROUP14_SHA1,
  /* ecdh-sha2-nistp256 */
-  SSH_KEX_ECDH_SHA2_NISTP256
+  SSH_KEX_ECDH_SHA2_NISTP256,
+  /* curve25519-sha256@libssh.org */
+  SSH_KEX_CURVE25519_SHA256_LIBSSH_ORG
 };

 struct ssh_crypto_struct {
@@ -60,6 +63,11 @@ struct ssh_crypto_struct {
    EC_KEY *ecdh_privkey;
    ssh_string ecdh_client_pubkey;
    ssh_string ecdh_server_pubkey;
+#endif
+#ifdef HAVE_CURVE25519
+    ssh_curve25519_privkey curve25519_privkey;
+    ssh_curve25519_pubkey curve25519_client_pubkey;
+    ssh_curve25519_pubkey curve25519_server_pubkey;
 #endif
    ssh_string dh_server_signature; /* information used by dh_handshake. */
    size_t digest_len; /* len of all the fields below */
--- a/include/libssh/curve25519.h
+++ b/include/libssh/curve25519.h
@@ -0,0 +1,46 @@
+/*
+ * This file is part of the SSH Library
+ *
+ * Copyright (c) 2013 by Aris Adamantiadis <aris@badcode.be>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation,
+ * version 2.1 of the License.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef CURVE25519_H_
+#define CURVE25519_H_
+
+#include "config.h"
+#include "libssh.h"
+
+#ifdef WITH_NACL
+
+#define HAVE_CURVE25519
+#include <nacl/crypto_scalarmult_curve25519.h>
+#define CURVE25519_PUBKEY_SIZE crypto_scalarmult_curve25519_BYTES
+#define CURVE25519_PRIVKEY_SIZE crypto_scalarmult_curve25519_SCALARBYTES
+
+typedef unsigned char ssh_curve25519_pubkey[CURVE25519_PUBKEY_SIZE];
+typedef unsigned char ssh_curve25519_privkey[CURVE25519_PRIVKEY_SIZE];
+
+#endif /* WITH_NACL */
+
+int ssh_client_curve25519_init(ssh_session session);
+int ssh_client_curve25519_reply(ssh_session session, ssh_buffer packet);
+
+#ifdef WITH_SERVER
+int ssh_server_curve25519_init(ssh_session session, ssh_buffer packet);
+#endif /* WITH_SERVER */
+
+#endif /* CURVE25519_H_ */
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -76,6 +76,18 @@ if (WITH_GSSAPI AND GSSAPI_FOUND)
  )
 endif (WITH_GSSAPI AND GSSAPI_FOUND)

+if (WITH_NACL AND NACL_FOUND)
+  set(LIBSSH_PRIVATE_INCLUDE_DIRS
+    ${LIBSSH_PRIVATE_INCLUDE_DIRS}
+    ${NACL_INCLUDE_DIR}
+  )
+
+  set(LIBSSH_LINK_LIBRARIES
+    ${LIBSSH_LINK_LIBRARIES}
+    ${NACL_LIBRARY}
+  )
+endif (WITH_NACL AND NACL_FOUND)
+
 set(LIBSSH_LINK_LIBRARIES
  ${LIBSSH_LINK_LIBRARIES}
  CACHE INTERNAL "libssh link libraries"
@@ -192,6 +204,13 @@ if (WITH_GSSAPI AND GSSAPI_FOUND)
  )
 endif (WITH_GSSAPI AND GSSAPI_FOUND)

+if (WITH_NACL)
+  set(libssh_SRCS
+    ${libssh_SRCS}
+    curve25519.c
+  )
+endif (WITH_NACL)
+
 include_directories(
  ${LIBSSH_PUBLIC_INCLUDE_DIRS}
  ${LIBSSH_PRIVATE_INCLUDE_DIRS}
--- a/src/client.c
+++ b/src/client.c
@@ -196,6 +196,11 @@ static int dh_handshake(ssh_session session) {
        case SSH_KEX_ECDH_SHA2_NISTP256:
          rc = ssh_client_ecdh_init(session);
          break;
+#endif
+#ifdef HAVE_CURVE25519
+        case SSH_KEX_CURVE25519_SHA256_LIBSSH_ORG:
+          rc = ssh_client_curve25519_init(session);
+          break;
 #endif
        default:
          rc = SSH_ERROR;
--- a/src/curve25519.c
+++ b/src/curve25519.c
@@ -0,0 +1,285 @@
+/*
+ * curve25519.c - Curve25519 ECDH functions for key exchange
+ * curve25519-sha256@libssh.org
+ *
+ * This file is part of the SSH Library
+ *
+ * Copyright (c) 2013      by Aris Adamantiadis <aris@badcode.be>
+ *
+ * The SSH Library is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, version 2.1 of the License.
+ *
+ * The SSH Library is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
+ * License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with the SSH Library; see the file COPYING.  If not, write to
+ * the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
+ * MA 02111-1307, USA.
+ */
+
+#include "config.h"
+
+#include "libssh/curve25519.h"
+#ifdef HAVE_CURVE25519
+
+#include "nacl/crypto_scalarmult_curve25519.h"
+#include "libssh/ssh2.h"
+#include "libssh/buffer.h"
+#include "libssh/priv.h"
+#include "libssh/session.h"
+#include "libssh/crypto.h"
+#include "libssh/dh.h"
+#include "libssh/pki.h"
+
+/** @internal
+ * @brief Starts curve25519-sha256@libssh.org key exchange
+ */
+int ssh_client_curve25519_init(ssh_session session){
+  ssh_string client_pubkey;
+  int rc;
+
+  rc = buffer_add_u8(session->out_buffer, SSH2_MSG_KEX_ECDH_INIT);
+  if (rc < 0) {
+      return SSH_ERROR;
+  }
+
+  rc = ssh_get_random(session->next_crypto->curve25519_privkey, CURVE25519_PRIVKEY_SIZE, 1);
+  if (rc == 0){
+	  ssh_set_error(session, SSH_FATAL, "PRNG error");
+	  return SSH_ERROR;
+  }
+
+  crypto_scalarmult_curve25519_base(session->next_crypto->curve25519_client_pubkey,
+		  session->next_crypto->curve25519_privkey);
+  client_pubkey = ssh_string_new(CURVE25519_PUBKEY_SIZE);
+  if (client_pubkey == NULL) {
+      return SSH_ERROR;
+  }
+  ssh_string_fill(client_pubkey, session->next_crypto->curve25519_client_pubkey,
+		  CURVE25519_PUBKEY_SIZE);
+  rc = buffer_add_ssh_string(session->out_buffer,client_pubkey);
+  if (rc < 0) {
+      ssh_string_free(client_pubkey);
+      return SSH_ERROR;
+  }
+
+  rc = packet_send(session);
+
+  return rc;
+}
+
+static int ssh_curve25519_build_k(ssh_session session) {
+  ssh_curve25519_pubkey k;
+  session->next_crypto->k = bignum_new();
+
+  if (session->next_crypto->k == NULL) {
+    return SSH_ERROR;
+  }
+
+  if (session->server)
+	  crypto_scalarmult_curve25519(k, session->next_crypto->curve25519_privkey,
+			  session->next_crypto->curve25519_client_pubkey);
+  else
+	  crypto_scalarmult_curve25519(k, session->next_crypto->curve25519_privkey,
+			  session->next_crypto->curve25519_server_pubkey);
+
+  BN_bin2bn(k, CURVE25519_PUBKEY_SIZE, session->next_crypto->k);
+
+#ifdef DEBUG_CRYPTO
+    ssh_print_hexa("Session server cookie",
+                   session->next_crypto->server_kex.cookie, 16);
+    ssh_print_hexa("Session client cookie",
+                   session->next_crypto->client_kex.cookie, 16);
+    ssh_print_bignum("Shared secret key", session->next_crypto->k);
+#endif
+
+  return 0;
+}
+
+/** @internal
+ * @brief parses a SSH_MSG_KEX_ECDH_REPLY packet and sends back
+ * a SSH_MSG_NEWKEYS
+ */
+int ssh_client_curve25519_reply(ssh_session session, ssh_buffer packet){
+  ssh_string q_s_string = NULL;
+  ssh_string pubkey = NULL;
+  ssh_string signature = NULL;
+  int rc;
+  pubkey = buffer_get_ssh_string(packet);
+  if (pubkey == NULL){
+    ssh_set_error(session,SSH_FATAL, "No public key in packet");
+    goto error;
+  }
+  /* this is the server host key */
+  session->next_crypto->server_pubkey = pubkey;
+  pubkey = NULL;
+
+  q_s_string = buffer_get_ssh_string(packet);
+  if (q_s_string == NULL) {
+	  ssh_set_error(session,SSH_FATAL, "No Q_S ECC point in packet");
+	  goto error;
+  }
+  if (ssh_string_len(q_s_string) != CURVE25519_PUBKEY_SIZE){
+	  ssh_set_error(session, SSH_FATAL, "Incorrect size for server Curve25519 public key: %d",
+			  ssh_string_len(q_s_string));
+	  ssh_string_free(q_s_string);
+	  goto error;
+  }
+  memcpy(session->next_crypto->curve25519_server_pubkey, ssh_string_data(q_s_string), CURVE25519_PUBKEY_SIZE);
+
+  signature = buffer_get_ssh_string(packet);
+  if (signature == NULL) {
+    ssh_set_error(session, SSH_FATAL, "No signature in packet");
+    goto error;
+  }
+  session->next_crypto->dh_server_signature = signature;
+  signature=NULL; /* ownership changed */
+  /* TODO: verify signature now instead of waiting for NEWKEYS */
+  if (ssh_curve25519_build_k(session) < 0) {
+    ssh_set_error(session, SSH_FATAL, "Cannot build k number");
+    goto error;
+  }
+
+  /* Send the MSG_NEWKEYS */
+  if (buffer_add_u8(session->out_buffer, SSH2_MSG_NEWKEYS) < 0) {
+    goto error;
+  }
+
+  rc=packet_send(session);
+  SSH_LOG(SSH_LOG_PROTOCOL, "SSH_MSG_NEWKEYS sent");
+  return rc;
+error:
+  return SSH_ERROR;
+}
+
+#ifdef WITH_SERVER
+
+/** @brief Parse a SSH_MSG_KEXDH_INIT packet (server) and send a
+ * SSH_MSG_KEXDH_REPLY
+ */
+int ssh_server_curve25519_init(ssh_session session, ssh_buffer packet){
+    /* ECDH keys */
+    ssh_string q_c_string;
+    ssh_string q_s_string;
+
+    /* SSH host keys (rsa,dsa,ecdsa) */
+    ssh_key privkey;
+    ssh_string sig_blob = NULL;
+    int rc;
+
+    /* Extract the client pubkey from the init packet */
+    q_c_string = buffer_get_ssh_string(packet);
+    if (q_c_string == NULL) {
+        ssh_set_error(session,SSH_FATAL, "No Q_C ECC point in packet");
+        return SSH_ERROR;
+    }
+    if (ssh_string_len(q_c_string) != CURVE25519_PUBKEY_SIZE){
+    	ssh_set_error(session, SSH_FATAL, "Incorrect size for server Curve25519 public key: %d",
+    			ssh_string_len(q_c_string));
+    	ssh_string_free(q_c_string);
+    	return SSH_ERROR;
+    }
+
+    memcpy(session->next_crypto->curve25519_client_pubkey,
+    		ssh_string_data(q_c_string), CURVE25519_PUBKEY_SIZE);
+    ssh_string_free(q_c_string);
+    /* Build server's keypair */
+
+    rc = ssh_get_random(session->next_crypto->curve25519_privkey, CURVE25519_PRIVKEY_SIZE, 1);
+    if (rc == 0){
+  	  ssh_set_error(session, SSH_FATAL, "PRNG error");
+  	  return SSH_ERROR;
+    }
+
+    crypto_scalarmult_curve25519_base(session->next_crypto->curve25519_server_pubkey,
+  		  session->next_crypto->curve25519_privkey);
+
+    q_s_string = ssh_string_new(CURVE25519_PUBKEY_SIZE);
+    if (q_s_string == NULL) {
+        return SSH_ERROR;
+    }
+
+    ssh_string_fill(q_s_string, session->next_crypto->curve25519_server_pubkey,
+    		CURVE25519_PUBKEY_SIZE);
+
+    rc = buffer_add_u8(session->out_buffer, SSH2_MSG_KEX_ECDH_REPLY);
+    if (rc < 0) {
+        ssh_set_error_oom(session);
+        return SSH_ERROR;
+    }
+
+    /* build k and session_id */
+    rc = ssh_curve25519_build_k(session);
+    if (rc < 0) {
+        ssh_set_error(session, SSH_FATAL, "Cannot build k number");
+        return SSH_ERROR;
+    }
+
+    /* privkey is not allocated */
+    rc = ssh_get_key_params(session, &privkey);
+    if (rc == SSH_ERROR) {
+        return SSH_ERROR;
+    }
+
+    rc = make_sessionid(session);
+    if (rc != SSH_OK) {
+        ssh_set_error(session, SSH_FATAL, "Could not create a session id");
+        return SSH_ERROR;
+    }
+
+    /* add host's public key */
+    rc = buffer_add_ssh_string(session->out_buffer,
+                               session->next_crypto->server_pubkey);
+    if (rc < 0) {
+        ssh_set_error_oom(session);
+        return SSH_ERROR;
+    }
+
+    /* add ecdh public key */
+    rc = buffer_add_ssh_string(session->out_buffer, q_s_string);
+    ssh_string_free(q_s_string);
+
+    if (rc < 0) {
+        ssh_set_error_oom(session);
+        return SSH_ERROR;
+    }
+    /* add signature blob */
+    sig_blob = ssh_srv_pki_do_sign_sessionid(session, privkey);
+    if (sig_blob == NULL) {
+        ssh_set_error(session, SSH_FATAL, "Could not sign the session id");
+        return SSH_ERROR;
+    }
+
+    rc = buffer_add_ssh_string(session->out_buffer, sig_blob);
+    ssh_string_free(sig_blob);
+    if (rc < 0) {
+        ssh_set_error_oom(session);
+        return SSH_ERROR;
+    }
+
+    SSH_LOG(SSH_LOG_PROTOCOL, "SSH_MSG_KEX_ECDH_REPLY sent");
+    rc = packet_send(session);
+    if (rc == SSH_ERROR) {
+        return SSH_ERROR;
+    }
+
+    /* Send the MSG_NEWKEYS */
+    rc = buffer_add_u8(session->out_buffer, SSH2_MSG_NEWKEYS);
+    if (rc < 0) {
+        return SSH_ERROR;;
+    }
+
+    session->dh_handshake_state = DH_STATE_NEWKEYS_SENT;
+    rc = packet_send(session);
+    SSH_LOG(SSH_LOG_PROTOCOL, "SSH_MSG_NEWKEYS sent");
+
+    return rc;
+}
+
+#endif /* WITH_SERVER */
+
+#endif /* HAVE_CURVE25519 */
--- a/src/dh.c
+++ b/src/dh.c
@@ -770,6 +770,18 @@ int make_sessionid(ssh_session session) {
    if (rc < 0) {
        goto error;
    }
+#endif
+#ifdef HAVE_CURVE25519
+  } else if(session->next_crypto->kex_type == SSH_KEX_CURVE25519_SHA256_LIBSSH_ORG){
+	  rc = buffer_add_u32(buf, htonl(CURVE25519_PUBKEY_SIZE));
+	  rc += buffer_add_data(buf, session->next_crypto->curve25519_client_pubkey,
+			  CURVE25519_PUBKEY_SIZE);
+	  rc += buffer_add_u32(buf, htonl(CURVE25519_PUBKEY_SIZE));
+	  rc += buffer_add_data(buf, session->next_crypto->curve25519_server_pubkey,
+			  CURVE25519_PUBKEY_SIZE);
+	  if (rc != SSH_OK) {
+		  goto error;
+      }
 #endif
  }
  num = make_bignum_string(session->next_crypto->k);
@@ -800,6 +812,7 @@ int make_sessionid(ssh_session session) {
                session->next_crypto->secret_hash);
      break;
    case SSH_KEX_ECDH_SHA2_NISTP256:
+    case SSH_KEX_CURVE25519_SHA256_LIBSSH_ORG:
      session->next_crypto->digest_len = SHA256_DIGEST_LENGTH;
      session->next_crypto->mac_type = SSH_MAC_SHA256;
      session->next_crypto->secret_hash = malloc(session->next_crypto->digest_len);
--- a/src/kex.c
+++ b/src/kex.c
@@ -34,6 +34,7 @@
 #include "libssh/session.h"
 #include "libssh/ssh2.h"
 #include "libssh/string.h"
+#include "libssh/curve25519.h"

 #ifdef HAVE_LIBGCRYPT
 # define BLOWFISH "blowfish-cbc,"
@@ -63,14 +64,21 @@
 #define ZLIB "none"
 #endif

-#ifdef HAVE_ECDH
-#define KEY_EXCHANGE "ecdh-sha2-nistp256,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1"
-#define HOSTKEYS "ecdsa-sha2-nistp256,ssh-rsa,ssh-dss"
+#ifdef HAVE_CURVE25519
+#define CURVE25519 "curve25519-sha256@libssh.org,"
 #else
-#define KEY_EXCHANGE "diffie-hellman-group14-sha1,diffie-hellman-group1-sha1"
-#define HOSTKEYS "ssh-rsa,ssh-dss"
+#define CURVE25519 ""
 #endif

+#ifdef HAVE_ECDH
+#define ECDH "ecdh-sha2-nistp256,"
+#define HOSTKEYS "ecdsa-sha2-nistp256,ssh-rsa,ssh-dss"
+#else
+#define HOSTKEYS "ssh-rsa,ssh-dss"
+#define ECDH ""
+#endif
+
+#define KEY_EXCHANGE CURVE25519 ECDH "diffie-hellman-group14-sha1,diffie-hellman-group1-sha1"
 #define KEX_METHODS_SIZE 10

 /* NOTE: This is a fixed API and the index is defined by ssh_kex_types_e */
@@ -412,6 +420,8 @@ int ssh_kex_select_methods (ssh_session session){
      session->next_crypto->kex_type=SSH_KEX_DH_GROUP14_SHA1;
    } else if(strcmp(session->next_crypto->kex_methods[SSH_KEX], "ecdh-sha2-nistp256") == 0){
      session->next_crypto->kex_type=SSH_KEX_ECDH_SHA2_NISTP256;
+    } else if(strcmp(session->next_crypto->kex_methods[SSH_KEX], "curve25519-sha256@libssh.org") == 0){
+      session->next_crypto->kex_type=SSH_KEX_CURVE25519_SHA256_LIBSSH_ORG;
    }

    return SSH_OK;
--- a/src/packet_cb.c
+++ b/src/packet_cb.c
@@ -35,6 +35,7 @@
 #include "libssh/session.h"
 #include "libssh/socket.h"
 #include "libssh/ssh2.h"
+#include "libssh/curve25519.h"

 /**
 * @internal
@@ -102,6 +103,11 @@ SSH_PACKET_CALLBACK(ssh_packet_dh_reply){
    case SSH_KEX_ECDH_SHA2_NISTP256:
      rc = ssh_client_ecdh_reply(session, packet);
      break;
+#endif
+#ifdef HAVE_CURVE25519
+    case SSH_KEX_CURVE25519_SHA256_LIBSSH_ORG:
+      rc = ssh_client_curve25519_reply(session, packet);
+      break;
 #endif
    default:
      ssh_set_error(session,SSH_FATAL,"Wrong kex type in ssh_packet_dh_reply");
--- a/src/server.c
+++ b/src/server.c
@@ -58,6 +58,7 @@
 #include "libssh/dh.h"
 #include "libssh/messages.h"
 #include "libssh/options.h"
+#include "libssh/curve25519.h"

 #define set_status(session, status) do {\
        if (session->common.callbacks && session->common.callbacks->connect_status_function) \
@@ -182,6 +183,11 @@ SSH_PACKET_CALLBACK(ssh_packet_kexdh_init){
      case SSH_KEX_ECDH_SHA2_NISTP256:
        rc = ssh_server_ecdh_init(session, packet);
        break;
+  #endif
+  #ifdef HAVE_CURVE25519
+      case SSH_KEX_CURVE25519_SHA256_LIBSSH_ORG:
+    	rc = ssh_server_curve25519_init(session, packet);
+    	break;
  #endif
      default:
        ssh_set_error(session,SSH_FATAL,"Wrong kex type in ssh_packet_kexdh_init");