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gpg: Print a warning for too much data encrypted with 3DES et al. 

* g10/filter.h (cipher_filter_context_t): Remove unused filed
'create_mdc'.  Turn field 'header' into a bit field.  Add new fields
'short_blklen_warn' and 'short_blklen_count'.
* g10/cipher.c (write_header): Print a warning if MDC is not used.
(cipher_filter): Print a warning for long messages encrypted with a
short block length algorithm.
--

Note that to test this warning in a reliable way compression needs to
be disabled.

Signed-off-by: Werner Koch <wk@gnupg.org>
This commit is contained in:
Werner Koch 2017-12-13 13:02:34 +01:00
parent b5333e13cb
commit 416cf9e9be
No known key found for this signature in database
GPG Key ID: E3FDFF218E45B72B
2 changed files with 26 additions and 5 deletions
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26
g10/cipher.c
View File

@ -64,6 +64,11 @@ write_header (cipher_filter_context_t *cfx, iobuf_t a)
if (DBG_HASHING)
gcry_md_debug (cfx->mdc_hash, "creatmdc");
}
else if (!opt.no_mdc_warn)
{
log_info ("WARNING: "
"encrypting without integrity protection is dangerous\n");
}
write_status_printf (STATUS_BEGIN_ENCRYPTION, "%d %d",
ed.mdc_method, cfx->dek->algo);
@ -91,7 +96,6 @@ write_header (cipher_filter_context_t *cfx, iobuf_t a)
BUG();
}
/* log_hexdump ("thekey", cfx->dek->key, cfx->dek->keylen); */
gcry_cipher_setkey (cfx->cipher_hd, cfx->dek->key, cfx->dek->keylen);
gcry_cipher_setiv (cfx->cipher_hd, NULL, 0);
@ -101,7 +105,11 @@ write_header (cipher_filter_context_t *cfx, iobuf_t a)
gcry_cipher_encrypt (cfx->cipher_hd, temp, nprefix+2, NULL, 0);
gcry_cipher_sync (cfx->cipher_hd);
iobuf_write (a, temp, nprefix+2);
cfx->header = 1;
cfx->short_blklen_warn = (blocksize < 16);
cfx->short_blklen_count = nprefix+2;
cfx->wrote_header = 1;
}
@ -122,11 +130,23 @@ cipher_filter (void *opaque, int control, iobuf_t a, byte *buf, size_t *ret_len)
else if (control == IOBUFCTRL_FLUSH) /* encrypt */
{
log_assert (a);
if (!cfx->header)
if (!cfx->wrote_header)
write_header (cfx, a);
if (cfx->mdc_hash)
gcry_md_write (cfx->mdc_hash, buf, size);
gcry_cipher_encrypt (cfx->cipher_hd, buf, size, NULL, 0);
if (cfx->short_blklen_warn)
{
cfx->short_blklen_count += size;
if (cfx->short_blklen_count > (150 * 1024 * 1024))
{
log_info ("WARNING: encrypting more than %d MiB with algorithm "
"%s should be avoided\n", 150,
openpgp_cipher_algo_name (cfx->dek->algo));
cfx->short_blklen_warn = 0; /* Don't show again. */
}
}
rc = iobuf_write (a, buf, size);
}
else if (control == IOBUFCTRL_FREE)

5
g10/filter.h
View File

@ -92,10 +92,11 @@ typedef struct {
DEK *dek;
u32 datalen;
gcry_cipher_hd_t cipher_hd;
int header;
unsigned int wrote_header : 1;
unsigned int short_blklen_warn : 1;
unsigned long short_blklen_count;
gcry_md_hd_t mdc_hash;
byte enchash[20];
int create_mdc; /* flag will be set by the cipher filter */
} cipher_filter_context_t;