xxxx_do_check( PKT_secret_key *sk, const char *tryagain_text, int mode,
               int *canceled )
{
    gpg_error_t err;
    byte *buffer;
    u16 csum=0;
    int i, res;
    size_t nbytes;

    if( sk->is_protected ) { /* remove the protection */
	DEK *dek = NULL;
	u32 keyid[4]; /* 4! because we need two of them */
	gcry_cipher_hd_t cipher_hd=NULL;
	PKT_secret_key *save_sk;

	if( sk->protect.s2k.mode == 1001 ) {
	    log_info(_("secret key parts are not available\n"));
	    return GPG_ERR_UNUSABLE_SECKEY;
	}
	if( sk->protect.algo == CIPHER_ALGO_NONE )
	    BUG();
	if( openpgp_cipher_test_algo( sk->protect.algo ) ) {
	    log_info(_("protection algorithm %d%s is not supported\n"),
			sk->protect.algo,sk->protect.algo==1?" (IDEA)":"" );
	    return GPG_ERR_CIPHER_ALGO;
	}
	if(gcry_md_test_algo (sk->protect.s2k.hash_algo))
	  {
	    log_info(_("protection digest %d is not supported\n"),
		     sk->protect.s2k.hash_algo);
	    return GPG_ERR_DIGEST_ALGO;
	  }
	keyid_from_sk( sk, keyid );
	keyid[2] = keyid[3] = 0;
	if (!sk->flags.primary)
          {
            keyid[2] = sk->main_keyid[0];
            keyid[3] = sk->main_keyid[1];
          }
	dek = passphrase_to_dek( keyid, sk->pubkey_algo, sk->protect.algo,
				 &sk->protect.s2k, mode,
                                 tryagain_text, canceled );
        if (!dek && canceled && *canceled)
	    return GPG_ERR_CANCELED;


	err = openpgp_cipher_open (&cipher_hd, sk->protect.algo,
				   GCRY_CIPHER_MODE_CFB,
				   (GCRY_CIPHER_SECURE
				    | (sk->protect.algo >= 100 ?
				       0 : GCRY_CIPHER_ENABLE_SYNC)));
        if (err)
          log_fatal ("cipher open failed: %s\n", gpg_strerror (err) );

	err = gcry_cipher_setkey (cipher_hd, dek->key, dek->keylen);
        if (err)
          log_fatal ("set key failed: %s\n", gpg_strerror (err) );

	xfree(dek);
	save_sk = copy_secret_key( NULL, sk );

	gcry_cipher_setiv ( cipher_hd, sk->protect.iv, sk->protect.ivlen );

	csum = 0;
	if( sk->version >= 4 ) {
            int ndata;
	    unsigned int ndatabits;
	    byte *p, *data;
            u16 csumc = 0;

	    i = pubkey_get_npkey(sk->pubkey_algo);

            assert ( gcry_mpi_get_flag (sk->skey[i], GCRYMPI_FLAG_OPAQUE ));
            p = gcry_mpi_get_opaque ( sk->skey[i], &ndatabits );
            ndata = (ndatabits+7)/8;

            if ( ndata > 1 )
              csumc = buf16_to_u16 (p+ndata-2);
	    data = xmalloc_secure ( ndata );
	    gcry_cipher_decrypt ( cipher_hd, data, ndata, p, ndata );
	    gcry_mpi_release (sk->skey[i]); sk->skey[i] = NULL ;

	    p = data;
            if (sk->protect.sha1chk) {
                /* This is the new SHA1 checksum method to detect
                   tampering with the key as used by the Klima/Rosa
                   attack */
                sk->csum = 0;
                csum = 1;
                if( ndata < 20 )
                    log_error("not enough bytes for SHA-1 checksum\n");
                else {
                    gcry_md_hd_t h;

                    if ( gcry_md_open (&h, DIGEST_ALGO_SHA1, 1))
                        BUG(); /* Algo not available. */
                    gcry_md_write (h, data, ndata - 20);
                    gcry_md_final (h);
                    if (!memcmp (gcry_md_read (h, DIGEST_ALGO_SHA1),
                                 data + ndata - 20, 20) )
                      {
                        /* Digest does match.  We have to keep the old
                           style checksum in sk->csum, so that the
                           test used for unprotected keys does work.
                           This test gets used when we are adding new
                           keys. */
                        sk->csum = csum = checksum (data, ndata-20);
                      }
                    gcry_md_close (h);
                }
            }
            else {
                if( ndata < 2 ) {
                    log_error("not enough bytes for checksum\n");
                    sk->csum = 0;
                    csum = 1;
                }
                else {
                    csum = checksum( data, ndata-2);
                    sk->csum = data[ndata-2] << 8 | data[ndata-1];
                    if ( sk->csum != csum ) {
                        /* This is a PGP 7.0.0 workaround */
                        sk->csum = csumc; /* take the encrypted one */
                    }
                }
            }

            /* Must check it here otherwise the mpi_read_xx would fail
               because the length may have an arbitrary value */
            if( sk->csum == csum ) {
                for( ; i < pubkey_get_nskey(sk->pubkey_algo); i++ ) {
                    if ( gcry_mpi_scan( &sk->skey[i], GCRYMPI_FMT_PGP,
                                        p, ndata, &nbytes))
                      {
                        /* Checksum was okay, but not correctly
                           decrypted.  */
                        sk->csum = 0;
                        csum = 1;
                        break;
                      }
                    ndata -= nbytes;
                    p += nbytes;
                }
                /* Note: at this point ndata should be 2 for a simple
                   checksum or 20 for the sha1 digest */
            }
	    xfree(data);
	}
	else {
	    for(i=pubkey_get_npkey(sk->pubkey_algo);
		    i < pubkey_get_nskey(sk->pubkey_algo); i++ ) {
                byte *p;
                size_t ndata;
                unsigned int ndatabits;

                assert (gcry_mpi_get_flag (sk->skey[i], GCRYMPI_FLAG_OPAQUE));
                p = gcry_mpi_get_opaque (sk->skey[i], &ndatabits);
                ndata = (ndatabits+7)/8;
                assert (ndata >= 2);
                assert (ndata == ((p[0] << 8 | p[1]) + 7)/8 + 2);
                buffer = xmalloc_secure (ndata);
		gcry_cipher_sync (cipher_hd);
                buffer[0] = p[0];
                buffer[1] = p[1];
                gcry_cipher_decrypt (cipher_hd, buffer+2, ndata-2,
                                     p+2, ndata-2);
                csum += checksum (buffer, ndata);
                gcry_mpi_release (sk->skey[i]);

		err = gcry_mpi_scan( &sk->skey[i], GCRYMPI_FMT_PGP,
				     buffer, ndata, &ndata );
		xfree (buffer);
                if (err)
                  {
                    /* Checksum was okay, but not correctly
                       decrypted.  */
                    sk->csum = 0;
                    csum = 1;
                    break;
                  }
/*  		csum += checksum_mpi (sk->skey[i]); */
	    }
	}
	gcry_cipher_close ( cipher_hd );

	/* Now let's see whether we have used the correct passphrase. */
	if( csum != sk->csum ) {
	    copy_secret_key( sk, save_sk );
            passphrase_clear_cache ( keyid, NULL, sk->pubkey_algo );
	    free_secret_key( save_sk );
	    return gpg_error (GPG_ERR_BAD_PASSPHRASE);
	}

	/* The checksum may fail, so we also check the key itself. */
	res = pk_check_secret_key ( sk->pubkey_algo, sk->skey );
	if( res ) {
	    copy_secret_key( sk, save_sk );
            passphrase_clear_cache ( keyid, NULL, sk->pubkey_algo );
	    free_secret_key( save_sk );
	    return gpg_error (GPG_ERR_BAD_PASSPHRASE);
	}
	free_secret_key( save_sk );
	sk->is_protected = 0;
    }
    else { /* not protected, assume it is okay if the checksum is okay */
	csum = 0;
	for(i=pubkey_get_npkey(sk->pubkey_algo);
		i < pubkey_get_nskey(sk->pubkey_algo); i++ ) {
	    csum += checksum_mpi( sk->skey[i] );
	}
	if( csum != sk->csum )
	    return GPG_ERR_CHECKSUM;
    }

    return 0;
}