Implement server-side support for sk-ecdsa U2F-backed keys (#142) * Implement server-side support for sk-ecdsa U2F-backed keys * Fix out-of-bounds read on normal ecdsa-sha2-[identifier] keys * Fix one more potential out-of-bounds read * Check if nistp256 curve is used in sk-ecdsa-sha2- key It's the only allowed curve per PROTOCOL.u2f specification * Implement server-side support for sk-ed25519 FIDO2-backed keys * Keys with type sk-* make no sense as host keys, so they should be disabled * fix typo * Make sk-ecdsa call buf_ecdsa_verify This reduces code duplication, the SK code just handles the different message format. * Reduce sk specific code The application id can be stored in signkey, then we don't need to call sk-specific functions from svr-authpubkey * Remove debugging output, which causes compilation errors with DEBUG_TRACE disabled * Proper cleanup of sk_app Co-authored-by: Matt Johnston <[email protected]>

#include "tommath_private.h"
#ifdef BN_MP_SQRMOD_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis */
/* SPDX-License-Identifier: Unlicense */

/* c = a * a (mod b) */
mp_err mp_sqrmod(const mp_int *a, const mp_int *b, mp_int *c)
{
   mp_err  err;
   mp_int  t;

   if ((err = mp_init(&t)) != MP_OKAY) {
      return err;
   }

   if ((err = mp_sqr(a, &t)) != MP_OKAY) {
      goto LBL_ERR;
   }
   err = mp_mod(&t, b, c);

LBL_ERR:
   mp_clear(&t);
   return err;
}
#endif