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Add protection for private keys at rest in RAM against speculation
and memory sidechannel attacks like Spectre, Meltdown, Rowhammer and
Rambleed. This change encrypts private keys when they are not in use
with a symmetic key that is derived from a relatively large "prekey"
consisting of random data (currently 16KB).

Attackers must recover the entire prekey with high accuracy before
they can attempt to decrypt the shielded private key, but the current
generation of attacks have bit error rates that, when applied
cumulatively to the entire prekey, make this unlikely.

Implementation-wise, keys are encrypted "shielded" when loaded and then
automatically and transparently unshielded when used for signatures or
when being saved/serialised.

Hopefully we can remove this in a few years time when computer
architecture has become less unsafe.

been in snaps for a bit already; thanks deraadt@

ok dtucker@ deraadt@

/* $OpenBSD: sshconnect.h,v 1.38 2019/06/21 04:21:05 djm Exp $ */

/*
 * Copyright (c) 2000 Markus Friedl.  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.
 */

typedef struct Sensitive Sensitive;
struct Sensitive {
	struct sshkey	**keys;
	int		nkeys;
};

struct addrinfo;
struct ssh;

int	 ssh_connect(struct ssh *, const char *, struct addrinfo *,
	    struct sockaddr_storage *, u_short, int, int, int *, int);
void	 ssh_kill_proxy_command(void);

void	 ssh_login(struct ssh *, Sensitive *, const char *,
    struct sockaddr *, u_short, struct passwd *, int);

int	 verify_host_key(char *, struct sockaddr *, struct sshkey *);

void	 get_hostfile_hostname_ipaddr(char *, struct sockaddr *, u_short,
    char **, char **);

void	 ssh_kex2(struct ssh *ssh, char *, struct sockaddr *, u_short);

void	 ssh_userauth2(struct ssh *ssh, const char *, const char *,
    char *, Sensitive *);

int	 ssh_local_cmd(const char *);

void	 maybe_add_key_to_agent(char *, struct sshkey *, char *, char *);