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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: authfd.h,v 1.45 2019/06/21 04:21:04 djm Exp $ */

/*
 * Author: Tatu Ylonen <ylo@cs.hut.fi>
 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
 *                    All rights reserved
 * Functions to interface with the SSH_AUTHENTICATION_FD socket.
 *
 * As far as I am concerned, the code I have written for this software
 * can be used freely for any purpose.  Any derived versions of this
 * software must be clearly marked as such, and if the derived work is
 * incompatible with the protocol description in the RFC file, it must be
 * called by a name other than "ssh" or "Secure Shell".
 */

#ifndef AUTHFD_H
#define AUTHFD_H

/* List of identities returned by ssh_fetch_identitylist() */
struct ssh_identitylist {
	size_t nkeys;
	struct sshkey **keys;
	char **comments;
};

int	ssh_get_authentication_socket(int *fdp);
void	ssh_close_authentication_socket(int sock);

int	ssh_lock_agent(int sock, int lock, const char *password);
int	ssh_fetch_identitylist(int sock, struct ssh_identitylist **idlp);
void	ssh_free_identitylist(struct ssh_identitylist *idl);
int	ssh_add_identity_constrained(int sock, struct sshkey *key,
	    const char *comment, u_int life, u_int confirm, u_int maxsign);
int	ssh_remove_identity(int sock, struct sshkey *key);
int	ssh_update_card(int sock, int add, const char *reader_id,
	    const char *pin, u_int life, u_int confirm);
int	ssh_remove_all_identities(int sock, int version);

int	ssh_agent_sign(int sock, const struct sshkey *key,
	    u_char **sigp, size_t *lenp,
	    const u_char *data, size_t datalen, const char *alg, u_int compat);

/* Messages for the authentication agent connection. */
#define SSH_AGENTC_REQUEST_RSA_IDENTITIES	1
#define SSH_AGENT_RSA_IDENTITIES_ANSWER		2
#define SSH_AGENTC_RSA_CHALLENGE		3
#define SSH_AGENT_RSA_RESPONSE			4
#define SSH_AGENT_FAILURE			5
#define SSH_AGENT_SUCCESS			6
#define SSH_AGENTC_ADD_RSA_IDENTITY		7
#define SSH_AGENTC_REMOVE_RSA_IDENTITY		8
#define SSH_AGENTC_REMOVE_ALL_RSA_IDENTITIES	9

/* private OpenSSH extensions for SSH2 */
#define SSH2_AGENTC_REQUEST_IDENTITIES		11
#define SSH2_AGENT_IDENTITIES_ANSWER		12
#define SSH2_AGENTC_SIGN_REQUEST		13
#define SSH2_AGENT_SIGN_RESPONSE		14
#define SSH2_AGENTC_ADD_IDENTITY		17
#define SSH2_AGENTC_REMOVE_IDENTITY		18
#define SSH2_AGENTC_REMOVE_ALL_IDENTITIES	19

/* smartcard */
#define SSH_AGENTC_ADD_SMARTCARD_KEY		20
#define SSH_AGENTC_REMOVE_SMARTCARD_KEY		21

/* lock/unlock the agent */
#define SSH_AGENTC_LOCK				22
#define SSH_AGENTC_UNLOCK			23

/* add key with constraints */
#define SSH_AGENTC_ADD_RSA_ID_CONSTRAINED	24
#define SSH2_AGENTC_ADD_ID_CONSTRAINED		25
#define SSH_AGENTC_ADD_SMARTCARD_KEY_CONSTRAINED 26

#define	SSH_AGENT_CONSTRAIN_LIFETIME		1
#define	SSH_AGENT_CONSTRAIN_CONFIRM		2
#define	SSH_AGENT_CONSTRAIN_MAXSIGN		3

/* extended failure messages */
#define SSH2_AGENT_FAILURE			30

/* additional error code for ssh.com's ssh-agent2 */
#define SSH_COM_AGENT2_FAILURE			102

#define	SSH_AGENT_OLD_SIGNATURE			0x01
#define	SSH_AGENT_RSA_SHA2_256			0x02
#define	SSH_AGENT_RSA_SHA2_512			0x04

#endif				/* AUTHFD_H */