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Extends the SK API to accept a set of key/value options for all
operations. These are intended to future-proof the API a little by
making it easier to specify additional fields for without having to
change the API version for each.

At present, only two options are defined: one to explicitly specify
the device for an operation (rather than accepting the middleware's
autoselection) and another to specify the FIDO2 username that may
be used when generating a resident key. These new options may be
invoked at key generation time via ssh-keygen -O

This also implements a suggestion from Markus to avoid "int" in favour
of uint32_t for the algorithm argument in the API, to make implementation
of ssh-sk-client/helper a little easier.

feedback, fixes and ok markus@

/* $OpenBSD: ssh-sk.h,v 1.9 2020/01/06 02:00:47 djm Exp $ */
/*
 * Copyright (c) 2019 Google LLC
 *
 * 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.
 */

#ifndef _SSH_SK_H
#define _SSH_SK_H 1

struct sshbuf;
struct sshkey;
struct sk_option;

/* Version of protocol expected from ssh-sk-helper */
#define SSH_SK_HELPER_VERSION		4

/* ssh-sk-helper messages */
#define SSH_SK_HELPER_ERROR		0	/* Only valid H->C */
#define SSH_SK_HELPER_SIGN		1
#define SSH_SK_HELPER_ENROLL		2
#define SSH_SK_HELPER_LOAD_RESIDENT	3

/*
 * Enroll (generate) a new security-key hosted private key of given type
 * via the specified provider middleware.
 * If challenge_buf is NULL then a random 256 bit challenge will be used.
 *
 * Returns 0 on success or a ssherr.h error code on failure.
 *
 * If successful and the attest_data buffer is not NULL then attestation
 * information is placed there.
 */
int sshsk_enroll(int type, const char *provider_path, const char *device,
    const char *application, const char *userid, uint8_t flags,
    const char *pin, struct sshbuf *challenge_buf,
    struct sshkey **keyp, struct sshbuf *attest);

/*
 * Calculate an ECDSA_SK or ED25519_SK signature using the specified key
 * and provider middleware.
 *
 * Returns 0 on success or a ssherr.h error code on failure.
 */
int sshsk_sign(const char *provider_path, struct sshkey *key,
    u_char **sigp, size_t *lenp, const u_char *data, size_t datalen,
    u_int compat, const char *pin);

/*
 * Enumerates and loads all SSH-compatible resident keys from a security
 * key.
 *
 * Returns 0 on success or a ssherr.h error code on failure.
 */
int sshsk_load_resident(const char *provider_path, const char *device,
    const char *pin, struct sshkey ***keysp, size_t *nkeysp);

#endif /* _SSH_SK_H */