options: Complete the transition to numeric toggles (`#if') For the sake of review, this commit alters only the code; the affiliated comments within the source files also need to be updated, but doing so now would obscure the operational changes that have been made here. * All on/off options have been switched to the numeric `#if' variant; that is the only way to make this `default_options.h.in' thing work in a reasonable manner. * There is now some very minor compile-time checking of the user's choice of options. * NO_FAST_EXPTMOD doesn't seem to be used, so it has been removed. * ENABLE_USER_ALGO_LIST was supposed to be renamed DROPBEAR_USER_ALGO_LIST, and this commit completes that work. * DROPBEAR_FUZZ seems to be a relatively new, as-yet undocumented option, which was added by the following commit: commit 6e0b539e9ca0b5628c6c5a3d118ad6a2e79e8039 Author: Matt Johnston <[email protected]> Date: Tue May 23 22:29:21 2017 +0800 split out checkpubkey_line() separately It has now been added to `sysoptions.h' and defined as `0' by default. * The configuration option `DROPBEAR_PASSWORD_ENV' is no longer listed in `default_options.h.in'; it is no longer meant to be set by the user, and is instead left to be defined in `sysoptions.h' (where it was already being defined) as merely the name of the environment variable in question: DROPBEAR_PASSWORD To enable or disable use of that environment variable, the user must now toggle `DROPBEAR_USE_DROPBEAR_PASSWORD'. * The sFTP support is now toggled by setting `DROPBEAR_SFTPSERVER', and the path of the sFTP server program is set independently through the usual SFTPSERVER_PATH.

/* LibTomCrypt, modular cryptographic library -- Tom St Denis
 *
 * LibTomCrypt is a library that provides various cryptographic
 * algorithms in a highly modular and flexible manner.
 *
 * The library is free for all purposes without any express
 * guarantee it works.
 */

#include "tomcrypt.h"

#ifdef LTC_CHACHA20POLY1305_MODE

/**
   Decrypt bytes of ciphertext with ChaCha20Poly1305
   @param st      The ChaCha20Poly1305 state
   @param in      The ciphertext
   @param inlen   The length of the input (octets)
   @param out     [out] The plaintext (length inlen)
   @return CRYPT_OK if successful
*/
int chacha20poly1305_decrypt(chacha20poly1305_state *st, const unsigned char *in, unsigned long inlen, unsigned char *out)
{
   unsigned char padzero[16] = { 0 };
   unsigned long padlen;
   int err;

   if (inlen == 0) return CRYPT_OK; /* nothing to do */
   LTC_ARGCHK(st != NULL);

   if (st->aadflg) {
      padlen = 16 - (unsigned long)(st->aadlen % 16);
      if (padlen < 16) {
        if ((err = poly1305_process(&st->poly, padzero, padlen)) != CRYPT_OK) return err;
      }
      st->aadflg = 0; /* no more AAD */
   }
   if (st->aadflg) st->aadflg = 0; /* no more AAD */
   if ((err = poly1305_process(&st->poly, in, inlen)) != CRYPT_OK)         return err;
   if ((err = chacha_crypt(&st->chacha, in, inlen, out)) != CRYPT_OK)      return err;
   st->ctlen += (ulong64)inlen;
   return CRYPT_OK;
}

#endif

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