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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@

/*
 * Copyright (c) 2012 Damien Miller <djm@mindrot.org>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

/* $OpenBSD: krl.h,v 1.7 2019/06/21 04:21:04 djm Exp $ */

#ifndef _KRL_H
#define _KRL_H

/* Functions to manage key revocation lists */

#define KRL_MAGIC		"SSHKRL\n\0"
#define KRL_FORMAT_VERSION	1

/* KRL section types */
#define KRL_SECTION_CERTIFICATES	1
#define KRL_SECTION_EXPLICIT_KEY	2
#define KRL_SECTION_FINGERPRINT_SHA1	3
#define KRL_SECTION_SIGNATURE		4
#define KRL_SECTION_FINGERPRINT_SHA256	5

/* KRL_SECTION_CERTIFICATES subsection types */
#define KRL_SECTION_CERT_SERIAL_LIST	0x20
#define KRL_SECTION_CERT_SERIAL_RANGE	0x21
#define KRL_SECTION_CERT_SERIAL_BITMAP	0x22
#define KRL_SECTION_CERT_KEY_ID		0x23

struct sshkey;
struct sshbuf;
struct ssh_krl;

struct ssh_krl *ssh_krl_init(void);
void ssh_krl_free(struct ssh_krl *krl);
void ssh_krl_set_version(struct ssh_krl *krl, u_int64_t version);
int ssh_krl_set_comment(struct ssh_krl *krl, const char *comment);
int ssh_krl_revoke_cert_by_serial(struct ssh_krl *krl,
    const struct sshkey *ca_key, u_int64_t serial);
int ssh_krl_revoke_cert_by_serial_range(struct ssh_krl *krl,
    const struct sshkey *ca_key, u_int64_t lo, u_int64_t hi);
int ssh_krl_revoke_cert_by_key_id(struct ssh_krl *krl,
    const struct sshkey *ca_key, const char *key_id);
int ssh_krl_revoke_key_explicit(struct ssh_krl *krl, const struct sshkey *key);
int ssh_krl_revoke_key_sha1(struct ssh_krl *krl, const u_char *p, size_t len);
int ssh_krl_revoke_key_sha256(struct ssh_krl *krl, const u_char *p, size_t len);
int ssh_krl_revoke_key(struct ssh_krl *krl, const struct sshkey *key);
int ssh_krl_to_blob(struct ssh_krl *krl, struct sshbuf *buf,
    struct sshkey **sign_keys, u_int nsign_keys);
int ssh_krl_from_blob(struct sshbuf *buf, struct ssh_krl **krlp,
    const struct sshkey **sign_ca_keys, size_t nsign_ca_keys);
int ssh_krl_check_key(struct ssh_krl *krl, const struct sshkey *key);
int ssh_krl_file_contains_key(const char *path, const struct sshkey *key);

#endif /* _KRL_H */