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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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19
g10/ChangeLog
View File

@ -1,3 +1,22 @@
2002-08-13 David Shaw <dshaw@jabberwocky.com>
* encode.c (encode_simple): Fix problem with using compression
algo 2 and 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.
2002-08-08 David Shaw <dshaw@jabberwocky.com>
* options.skel: Some language tweaks, and remove the

21
g10/cipher.c
View File

@ -47,31 +47,16 @@ write_header( cipher_filter_context_t *cfx, IOBUF a )
byte temp[18];
unsigned blocksize;
unsigned nprefix;
int use_mdc;
blocksize = cipher_get_blocksize( cfx->dek->algo );
if( blocksize < 8 || blocksize > 16 )
log_fatal("unsupported blocksize %u\n", blocksize );
use_mdc = cfx->dek->use_mdc;
if( blocksize != 8 )
use_mdc = 1; /* Hack: enable it for all modern ciphers */
/* Note: We should remove this hack as soon as a reasonable number of keys
are carrying the MDC flag. But always keep the hack for conventional
encryption */
if (opt.force_mdc)
use_mdc = 1;
if( opt.rfc2440 || opt.rfc1991 || opt.disable_mdc )
use_mdc = 0; /* override - rfc2440 does not know about MDC */
memset( &ed, 0, sizeof ed );
ed.len = cfx->datalen;
ed.extralen = blocksize+2;
ed.new_ctb = !ed.len && !opt.rfc1991;
if( use_mdc ) {
if( cfx->dek->use_mdc ) {
ed.mdc_method = DIGEST_ALGO_SHA1;
cfx->mdc_hash = md_open( DIGEST_ALGO_SHA1, 0 );
if ( DBG_HASHING )
@ -86,7 +71,7 @@ write_header( cipher_filter_context_t *cfx, IOBUF a )
}
init_packet( &pkt );
pkt.pkttype = use_mdc? PKT_ENCRYPTED_MDC : PKT_ENCRYPTED;
pkt.pkttype = cfx->dek->use_mdc? PKT_ENCRYPTED_MDC : PKT_ENCRYPTED;
pkt.pkt.encrypted = &ed;
if( build_packet( a, &pkt ))
log_bug("build_packet(ENCR_DATA) failed\n");
@ -96,7 +81,7 @@ write_header( cipher_filter_context_t *cfx, IOBUF a )
temp[nprefix+1] = temp[nprefix-1];
print_cipher_algo_note( cfx->dek->algo );
cfx->cipher_hd = cipher_open( cfx->dek->algo,
use_mdc? CIPHER_MODE_CFB
cfx->dek->use_mdc? CIPHER_MODE_CFB
: CIPHER_MODE_AUTO_CFB, 1 );
/* log_hexdump( "thekey", cfx->dek->key, cfx->dek->keylen );*/
cipher_setkey( cfx->cipher_hd, cfx->dek->key, cfx->dek->keylen );

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 )

5
g10/g10.c
View File

@ -1400,12 +1400,15 @@ main( int argc, char **argv )
opt.rfc1991 = 1;
opt.rfc2440 = 0;
opt.force_v4_certs = 0;
opt.sk_comments = 0;
opt.disable_mdc = 1;
opt.escape_from = 1;
break;
case oOpenPGP:
/* TODO: When 2440bis becomes a RFC, these may need
changing. */
opt.rfc1991 = 0;
opt.rfc2440 = 1;
opt.disable_mdc = 1;
opt.allow_non_selfsigned_uid = 1;
opt.allow_freeform_uid = 1;
opt.pgp2_workarounds = 0;

9
g10/pkclist.c
View File

@ -1159,6 +1159,11 @@ select_algo_from_prefs(PK_LIST pk_list, int preftype, int request, void *hint)
i = -1;
any = 0;
/* Can we use the requested algorithm? */
if(request>-1 && (bits[request/32] & (1<<(request%32))) &&
algo_available(preftype,request,hint))
return request;
/* If we have personal prefs set, use them instead of the last key */
if(preftype==PREFTYPE_SYM && opt.personal_cipher_prefs)
prefs=opt.personal_cipher_prefs;
@ -1190,10 +1195,6 @@ select_algo_from_prefs(PK_LIST pk_list, int preftype, int request, void *hint)
}
}
/* Can we use the requested algorithm? */
if(request>-1 && request==i)
return i;
#if 0
log_debug("prefs of type %d: selected %d\n", preftype, i );
#endif