Fix handling of replies to global requests (#112) The current code assumes that all global requests want / need a reply. This isn't always true and the request itself indicates if it wants a reply or not. It causes a specific problem with [email protected] messages. These are sent by OpenSSH after authentication to inform the client of potential other host keys for the host. This can be used to add a new type of host key or to rotate host keys. The initial information message from the server is sent as a global request, but with want_reply set to false. This means that the server doesn't expect an answer to this message. Instead the client needs to send a prove request as a reply if it wants to receive proof of ownership for the host keys. The bug doesn't cause any current problems with due to how OpenSSH treats receiving the failure message. It instead treats it as a keepalive message and further ignores it. Arguably this is a protocol violation though of Dropbear and it is only accidental that it doesn't cause a problem with OpenSSH. The bug was found when adding host keys support to libssh, which is more strict protocol wise and treats the unexpected failure message an error, also see https://gitlab.com/libssh/libssh-mirror/-/merge_requests/145 for more information. The fix here is to honor the want_reply flag in the global request and to only send a reply if the other side expects a reply.

#ifndef DROPBEAR_ECDSA_H_
#define DROPBEAR_ECDSA_H_

#include "includes.h"
#include "buffer.h"
#include "signkey.h"

#if DROPBEAR_ECDSA

/* prefer 256 or 384 since those are SHOULD for
   draft-ietf-curdle-ssh-kex-sha2.txt */
#if DROPBEAR_ECC_256
#define ECDSA_DEFAULT_SIZE 256
#elif DROPBEAR_ECC_384
#define ECDSA_DEFAULT_SIZE 384
#elif DROPBEAR_ECC_521
#define ECDSA_DEFAULT_SIZE 521
#else
#error ECDSA cannot be enabled without enabling at least one size (256, 384, 521)
#endif

ecc_key *gen_ecdsa_priv_key(unsigned int bit_size);
ecc_key *buf_get_ecdsa_pub_key(buffer* buf);
ecc_key *buf_get_ecdsa_priv_key(buffer *buf);
void buf_put_ecdsa_pub_key(buffer *buf, ecc_key *key);
void buf_put_ecdsa_priv_key(buffer *buf, ecc_key *key);
enum signkey_type ecdsa_signkey_type(const ecc_key * key);

void buf_put_ecdsa_sign(buffer *buf, const ecc_key *key, const buffer *data_buf);
int buf_ecdsa_verify(buffer *buf, const ecc_key *key, const buffer *data_buf);
/* Returns 1 on success */
int signkey_is_ecdsa(enum signkey_type type);

#endif

#endif /* DROPBEAR_ECDSA_H_ */