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* encode.c (encode_simple): Fix problem with using compression algo 2 and

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symmetric compressed files.

* encode.c (encode_simple, encode_crypt): If we are not using a MDC,
compress even if a file is already compressed.  This is to help against
the chosen ciphertext attack.

* pkclist.c (select_algo_from_prefs): Fix requested algorithm bug so the
request succeeds even if the requested algorithm is not the first found.

* cipher.c (write_header), encode.c (use_mdc, encode_simple, encode_crypt,
encrypt_filter), g10.c (main): Be more eager to use a MDC.  We use a MDC
if the keys directly support it, if the keys list AES (any) or TWOFISH
anywhere in the prefs, or if the cipher chosen does not have a 64 bit
blocksize.
This commit is contained in:
David Shaw 2002-08-13 19:00:23 +00:00
parent d1f6ccd154
commit 1111da19a8
5 changed files with 114 additions and 47 deletions
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107
g10/encode.c
View file

@ -102,6 +102,52 @@ encode_sesskey( DEK *dek, DEK **ret_dek, byte *enckey )
*ret_dek = c;
}
/* We try very hard to use a MDC */
static int
use_mdc(PK_LIST pk_list,int algo)
{
/* --force-mdc overrides --disable-mdc */
if(opt.force_mdc)
return 1;
if(opt.disable_mdc)
return 0;
/* Do the keys really support MDC? */
if(select_mdc_from_pklist(pk_list))
return 1;
/* The keys don't support MDC, so now we do a bit of a hack - if any
of the AESes or TWOFISH are in the prefs, we assume that the user
can handle a MDC. This is valid for PGP 7, which can handle MDCs
though it will not generate them. 2440bis allows this, by the
way. */
if(select_algo_from_prefs(pk_list,PREFTYPE_SYM,
CIPHER_ALGO_AES,NULL)==CIPHER_ALGO_AES)
return 1;
if(select_algo_from_prefs(pk_list,PREFTYPE_SYM,
CIPHER_ALGO_AES192,NULL)==CIPHER_ALGO_AES192)
return 1;
if(select_algo_from_prefs(pk_list,PREFTYPE_SYM,
CIPHER_ALGO_AES256,NULL)==CIPHER_ALGO_AES256)
return 1;
if(select_algo_from_prefs(pk_list,PREFTYPE_SYM,
CIPHER_ALGO_TWOFISH,NULL)==CIPHER_ALGO_TWOFISH)
return 1;
/* Last try. Use MDC for the modern ciphers. */
if(cipher_get_blocksize(algo)!=8)
return 1;
return 0; /* No MDC */
}
static int
encode_simple( const char *filename, int mode, int compat )
{
@ -126,15 +172,6 @@ encode_simple( const char *filename, int mode, int compat )
memset( &tfx, 0, sizeof tfx);
init_packet(&pkt);
if (opt.compress == -1 && is_file_compressed(filename, &rc))
{
if (opt.verbose)
log_info(_("`%s' already compressed\n"), filename);
do_compress = 0;
}
if (rc)
return rc;
/* prepare iobufs */
if( !(inp = iobuf_open(filename)) ) {
log_error(_("%s: can't open: %s\n"), filename? filename: "[stdin]",
@ -175,9 +212,19 @@ encode_simple( const char *filename, int mode, int compat )
encode_sesskey( cfx.dek, &dek, enckey );
m_free( cfx.dek ); cfx.dek = dek;
}
cfx.dek->use_mdc=use_mdc(NULL,cfx.dek->algo);
}
if( (rc = open_outfile( filename, opt.armor? 1:0, &out )) ) {
if (opt.compress == -1 && cfx.dek && cfx.dek->use_mdc &&
is_file_compressed(filename, &rc))
{
if (opt.verbose)
log_info(_("`%s' already compressed\n"), filename);
do_compress = 0;
}
if( rc || (rc = open_outfile( filename, opt.armor? 1:0, &out )) ) {
iobuf_cancel(inp);
m_free(cfx.dek);
m_free(s2k);
@ -271,7 +318,12 @@ encode_simple( const char *filename, int mode, int compat )
iobuf_push_filter( out, cipher_filter, &cfx );
/* register the compress filter */
if( do_compress )
{
zfx.algo=opt.def_compress_algo;
if(zfx.algo==-1)
zfx.algo=DEFAULT_COMPRESS_ALGO;
iobuf_push_filter( out, compress_filter, &zfx );
}
/* do the work */
if (!opt.no_literal) {
@ -351,18 +403,6 @@ encode_crypt( const char *filename, STRLIST remusr )
}
}
if (opt.compress == -1 && is_file_compressed(filename, &rc2))
{
if (opt.verbose)
log_info(_("`%s' already compressed\n"), filename);
do_compress = 0;
}
if (rc2)
{
rc = rc2;
goto leave;
}
/* prepare iobufs */
if( !(inp = iobuf_open(filename)) ) {
log_error(_("can't open %s: %s\n"), filename? filename: "[stdin]",
@ -423,7 +463,26 @@ encode_crypt( const char *filename, STRLIST remusr )
cfx.dek->algo = opt.def_cipher_algo;
}
cfx.dek->use_mdc = select_mdc_from_pklist (pk_list);
cfx.dek->use_mdc=use_mdc(pk_list,cfx.dek->algo);
/* Only do the is-file-already-compressed check if we are using a
MDC. This forces compressed files to be re-compressed if we do
not have a MDC to give some protection against chosen
ciphertext attacks. */
if (opt.compress == -1 && cfx.dek->use_mdc &&
is_file_compressed(filename, &rc2) )
{
if (opt.verbose)
log_info(_("`%s' already compressed\n"), filename);
do_compress = 0;
}
if (rc2)
{
rc = rc2;
goto leave;
}
make_session_key( cfx.dek );
if( DBG_CIPHER )
@ -578,7 +637,7 @@ encrypt_filter( void *opaque, int control,
efx->cfx.dek->algo = opt.def_cipher_algo;
}
efx->cfx.dek->use_mdc = select_mdc_from_pklist (efx->pk_list);
efx->cfx.dek->use_mdc = use_mdc(efx->pk_list,efx->cfx.dek->algo);
make_session_key( efx->cfx.dek );
if( DBG_CIPHER )