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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: sshkey.h,v 1.32 2019/06/21 04:21:05 djm Exp $ */

/*
 * Copyright (c) 2000, 2001 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.
 */
#ifndef SSHKEY_H
#define SSHKEY_H

#include <sys/types.h>

#ifdef WITH_OPENSSL
#include <openssl/rsa.h>
#include <openssl/dsa.h>
#include <openssl/ec.h>
#include <openssl/ecdsa.h>
#else /* OPENSSL */
#define BIGNUM		void
#define RSA		void
#define DSA		void
#define EC_KEY		void
#define EC_GROUP	void
#define EC_POINT	void
#endif /* WITH_OPENSSL */

#define SSH_RSA_MINIMUM_MODULUS_SIZE	1024
#define SSH_KEY_MAX_SIGN_DATA_SIZE	(1 << 20)

struct sshbuf;

/* Key types */
enum sshkey_types {
	KEY_RSA,
	KEY_DSA,
	KEY_ECDSA,
	KEY_ED25519,
	KEY_RSA_CERT,
	KEY_DSA_CERT,
	KEY_ECDSA_CERT,
	KEY_ED25519_CERT,
	KEY_XMSS,
	KEY_XMSS_CERT,
	KEY_UNSPEC
};

/* Default fingerprint hash */
#define SSH_FP_HASH_DEFAULT	SSH_DIGEST_SHA256

/* Fingerprint representation formats */
enum sshkey_fp_rep {
	SSH_FP_DEFAULT = 0,
	SSH_FP_HEX,
	SSH_FP_BASE64,
	SSH_FP_BUBBLEBABBLE,
	SSH_FP_RANDOMART
};

/* Private key serialisation formats, used on the wire */
enum sshkey_serialize_rep {
	SSHKEY_SERIALIZE_DEFAULT = 0,
	SSHKEY_SERIALIZE_STATE = 1,
	SSHKEY_SERIALIZE_FULL = 2,
	SSHKEY_SERIALIZE_INFO = 254,
};

/* key is stored in external hardware */
#define SSHKEY_FLAG_EXT		0x0001

#define SSHKEY_CERT_MAX_PRINCIPALS	256
/* XXX opaquify? */
struct sshkey_cert {
	struct sshbuf	*certblob; /* Kept around for use on wire */
	u_int		 type; /* SSH2_CERT_TYPE_USER or SSH2_CERT_TYPE_HOST */
	u_int64_t	 serial;
	char		*key_id;
	u_int		 nprincipals;
	char		**principals;
	u_int64_t	 valid_after, valid_before;
	struct sshbuf	*critical;
	struct sshbuf	*extensions;
	struct sshkey	*signature_key;
	char		*signature_type;
};

/* XXX opaquify? */
struct sshkey {
	int	 type;
	int	 flags;
	RSA	*rsa;
	DSA	*dsa;
	int	 ecdsa_nid;	/* NID of curve */
	EC_KEY	*ecdsa;
	u_char	*ed25519_sk;
	u_char	*ed25519_pk;
	char	*xmss_name;
	char	*xmss_filename;	/* for state file updates */
	void	*xmss_state;	/* depends on xmss_name, opaque */
	u_char	*xmss_sk;
	u_char	*xmss_pk;
	struct sshkey_cert *cert;
	u_char	*shielded_private;
	size_t	shielded_len;
	u_char	*shield_prekey;
	size_t	shield_prekey_len;
};

#define	ED25519_SK_SZ	crypto_sign_ed25519_SECRETKEYBYTES
#define	ED25519_PK_SZ	crypto_sign_ed25519_PUBLICKEYBYTES

struct sshkey	*sshkey_new(int);
void		 sshkey_free(struct sshkey *);
int		 sshkey_equal_public(const struct sshkey *,
    const struct sshkey *);
int		 sshkey_equal(const struct sshkey *, const struct sshkey *);
char		*sshkey_fingerprint(const struct sshkey *,
    int, enum sshkey_fp_rep);
int		 sshkey_fingerprint_raw(const struct sshkey *k,
    int, u_char **retp, size_t *lenp);
const char	*sshkey_type(const struct sshkey *);
const char	*sshkey_cert_type(const struct sshkey *);
int		 sshkey_format_text(const struct sshkey *, struct sshbuf *);
int		 sshkey_write(const struct sshkey *, FILE *);
int		 sshkey_read(struct sshkey *, char **);
u_int		 sshkey_size(const struct sshkey *);

int		 sshkey_generate(int type, u_int bits, struct sshkey **keyp);
int		 sshkey_from_private(const struct sshkey *, struct sshkey **);

int		 sshkey_is_shielded(struct sshkey *);
int		 sshkey_shield_private(struct sshkey *);
int		 sshkey_unshield_private(struct sshkey *);

int	 sshkey_type_from_name(const char *);
int	 sshkey_is_cert(const struct sshkey *);
int	 sshkey_type_is_cert(int);
int	 sshkey_type_plain(int);
int	 sshkey_to_certified(struct sshkey *);
int	 sshkey_drop_cert(struct sshkey *);
int	 sshkey_cert_copy(const struct sshkey *, struct sshkey *);
int	 sshkey_cert_check_authority(const struct sshkey *, int, int,
    const char *, const char **);
size_t	 sshkey_format_cert_validity(const struct sshkey_cert *,
    char *, size_t) __attribute__((__bounded__(__string__, 2, 3)));
int	 sshkey_check_cert_sigtype(const struct sshkey *, const char *);

int	 sshkey_certify(struct sshkey *, struct sshkey *, const char *);
/* Variant allowing use of a custom signature function (e.g. for ssh-agent) */
typedef int sshkey_certify_signer(struct sshkey *, u_char **, size_t *,
    const u_char *, size_t, const char *, u_int, void *);
int	 sshkey_certify_custom(struct sshkey *, struct sshkey *, const char *,
    sshkey_certify_signer *, void *);

int		 sshkey_ecdsa_nid_from_name(const char *);
int		 sshkey_curve_name_to_nid(const char *);
const char *	 sshkey_curve_nid_to_name(int);
u_int		 sshkey_curve_nid_to_bits(int);
int		 sshkey_ecdsa_bits_to_nid(int);
int		 sshkey_ecdsa_key_to_nid(EC_KEY *);
int		 sshkey_ec_nid_to_hash_alg(int nid);
int		 sshkey_ec_validate_public(const EC_GROUP *, const EC_POINT *);
int		 sshkey_ec_validate_private(const EC_KEY *);
const char	*sshkey_ssh_name(const struct sshkey *);
const char	*sshkey_ssh_name_plain(const struct sshkey *);
int		 sshkey_names_valid2(const char *, int);
char		*sshkey_alg_list(int, int, int, char);

int	 sshkey_from_blob(const u_char *, size_t, struct sshkey **);
int	 sshkey_fromb(struct sshbuf *, struct sshkey **);
int	 sshkey_froms(struct sshbuf *, struct sshkey **);
int	 sshkey_to_blob(const struct sshkey *, u_char **, size_t *);
int	 sshkey_to_base64(const struct sshkey *, char **);
int	 sshkey_putb(const struct sshkey *, struct sshbuf *);
int	 sshkey_puts(const struct sshkey *, struct sshbuf *);
int	 sshkey_puts_opts(const struct sshkey *, struct sshbuf *,
    enum sshkey_serialize_rep);
int	 sshkey_plain_to_blob(const struct sshkey *, u_char **, size_t *);
int	 sshkey_putb_plain(const struct sshkey *, struct sshbuf *);

int	 sshkey_sign(struct sshkey *, u_char **, size_t *,
    const u_char *, size_t, const char *, u_int);
int	 sshkey_verify(const struct sshkey *, const u_char *, size_t,
    const u_char *, size_t, const char *, u_int);
int	 sshkey_check_sigtype(const u_char *, size_t, const char *);
const char *sshkey_sigalg_by_name(const char *);

/* for debug */
void	sshkey_dump_ec_point(const EC_GROUP *, const EC_POINT *);
void	sshkey_dump_ec_key(const EC_KEY *);

/* private key parsing and serialisation */
int	sshkey_private_serialize(struct sshkey *key, struct sshbuf *buf);
int	sshkey_private_serialize_opt(struct sshkey *key, struct sshbuf *buf,
    enum sshkey_serialize_rep);
int	sshkey_private_deserialize(struct sshbuf *buf,  struct sshkey **keyp);

/* private key file format parsing and serialisation */
int	sshkey_private_to_fileblob(struct sshkey *key, struct sshbuf *blob,
    const char *passphrase, const char *comment,
    int force_new_format, const char *new_format_cipher, int new_format_rounds);
int	sshkey_parse_private_fileblob(struct sshbuf *buffer,
    const char *passphrase, struct sshkey **keyp, char **commentp);
int	sshkey_parse_private_fileblob_type(struct sshbuf *blob, int type,
    const char *passphrase, struct sshkey **keyp, char **commentp);

/* XXX should be internal, but used by ssh-keygen */
int ssh_rsa_complete_crt_parameters(struct sshkey *, const BIGNUM *);

/* stateful keys (e.g. XMSS) */
typedef void sshkey_printfn(const char *, ...) __attribute__((format(printf, 1, 2)));
int	 sshkey_set_filename(struct sshkey *, const char *);
int	 sshkey_enable_maxsign(struct sshkey *, u_int32_t);
u_int32_t sshkey_signatures_left(const struct sshkey *);
int	 sshkey_forward_state(const struct sshkey *, u_int32_t, sshkey_printfn *);
int	 sshkey_private_serialize_maxsign(struct sshkey *key, struct sshbuf *buf,
    u_int32_t maxsign, sshkey_printfn *pr);

#ifdef SSHKEY_INTERNAL
int ssh_rsa_sign(const struct sshkey *key,
    u_char **sigp, size_t *lenp, const u_char *data, size_t datalen,
    const char *ident);
int ssh_rsa_verify(const struct sshkey *key,
    const u_char *sig, size_t siglen, const u_char *data, size_t datalen,
    const char *alg);
int ssh_dss_sign(const struct sshkey *key, u_char **sigp, size_t *lenp,
    const u_char *data, size_t datalen, u_int compat);
int ssh_dss_verify(const struct sshkey *key,
    const u_char *signature, size_t signaturelen,
    const u_char *data, size_t datalen, u_int compat);
int ssh_ecdsa_sign(const struct sshkey *key, u_char **sigp, size_t *lenp,
    const u_char *data, size_t datalen, u_int compat);
int ssh_ecdsa_verify(const struct sshkey *key,
    const u_char *signature, size_t signaturelen,
    const u_char *data, size_t datalen, u_int compat);
int ssh_ed25519_sign(const struct sshkey *key, u_char **sigp, size_t *lenp,
    const u_char *data, size_t datalen, u_int compat);
int ssh_ed25519_verify(const struct sshkey *key,
    const u_char *signature, size_t signaturelen,
    const u_char *data, size_t datalen, u_int compat);
int ssh_xmss_sign(const struct sshkey *key, u_char **sigp, size_t *lenp,
    const u_char *data, size_t datalen, u_int compat);
int ssh_xmss_verify(const struct sshkey *key,
    const u_char *signature, size_t signaturelen,
    const u_char *data, size_t datalen, u_int compat);
#endif

#ifndef WITH_OPENSSL
#undef RSA
#undef DSA
#undef EC_KEY
#undef EC_GROUP
#undef EC_POINT
#endif /* WITH_OPENSSL */

#endif /* SSHKEY_H */