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sm: Support AES-GCM decryption.

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* tests/cms/samplemsgs/: Add sample messages.
* sm/gpgsm.c (main): Use gpgrt_fcancel on decryption error.
* sm/decrypt.c (decrypt_gcm_filter): New.
(gpgsm_decrypt): Use this filter if requested.  Check authtag.
--

Note that the sample message pwri-sample.gcm.p7m is broken: The
authtag is duplicated to the authEncryptedContentInfo.  I used a
temporary code during testing hack to that test message out.
This commit is contained in:
Werner Koch 2021-06-02 11:03:55 +02:00
parent a8209b001c
commit 4980fb3c6d
No known key found for this signature in database
GPG key ID: E3FDFF218E45B72B
8 changed files with 96 additions and 7 deletions
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82
sm/decrypt.c
View file

@ -37,6 +37,15 @@
#include "../common/tlv.h"
#include "../common/compliance.h"
/* We can provide an enum value which is only availabale with KSBA
* 1.6.0 so that we can compile even against older versions. Some
* calls will of course return an error in this case. This value is
* currently not used because the cipher mode is sufficient here. */
/* #if KSBA_VERSION_NUMBER < 0x010600 /\* 1.6.0 *\/ */
/* # define KSBA_CT_AUTHENVELOPED_DATA 10 */
/* #endif */
struct decrypt_filter_parm_s
{
int algo;
@ -911,6 +920,14 @@ prepare_decryption (ctrl_t ctrl, const char *hexkeygrip,
goto leave;
}
if (parm->mode == GCRY_CIPHER_MODE_GCM)
{
/* GCM mode really sucks in CMS. We need to know the AAD before
* we start decrypting but CMS puts the AAD after the content.
* Thus temporary files are required. Let's hope that no real
* messages with actual AAD are ever used. OCB Rules! */
}
leave:
xfree (seskey);
return rc;
@ -1010,6 +1027,36 @@ decrypt_filter (void *arg,
}
/* This is the GCM version of decrypt_filter. */
static gpg_error_t
decrypt_gcm_filter (void *arg,
const void *inbuf, size_t inlen, size_t *inused,
void *outbuf, size_t maxoutlen, size_t *outlen)
{
struct decrypt_filter_parm_s *parm = arg;
if (!inlen)
return gpg_error (GPG_ERR_BUG);
if (maxoutlen < parm->blklen)
return gpg_error (GPG_ERR_BUG);
if (inlen > maxoutlen)
inlen = maxoutlen;
*inused = inlen;
if (inlen)
{
gcry_cipher_decrypt (parm->hd, outbuf, inlen, inbuf, inlen);
*outlen = inlen;
parm->any_data = 1;
}
else
*outlen = 0;
return 0;
}
/* Perform a decrypt operation. */
int
@ -1332,9 +1379,11 @@ gpgsm_decrypt (ctrl_t ctrl, int in_fd, estream_t out_fp)
else
{ /* setup the bulk decrypter */
any_key = 1;
ksba_writer_set_filter (writer,
decrypt_filter,
&dfparm);
ksba_writer_set_filter
(writer,
dfparm.mode == GCRY_CIPHER_MODE_GCM?
decrypt_gcm_filter : decrypt_filter,
&dfparm);
if (dfparm.is_de_vs
&& gnupg_gcrypt_is_compliant (CO_DE_VS))
@ -1389,7 +1438,11 @@ gpgsm_decrypt (ctrl_t ctrl, int in_fd, estream_t out_fp)
else if (stopreason == KSBA_SR_END_DATA)
{
ksba_writer_set_filter (writer, NULL, NULL);
if (dfparm.any_data)
if (dfparm.mode == GCRY_CIPHER_MODE_GCM)
{
/* Nothing yet to do. We wait for the ready event. */
}
else if (dfparm.any_data )
{ /* write the last block with padding removed */
int i, npadding = dfparm.lastblock[dfparm.blklen-1];
if (!npadding || npadding > dfparm.blklen)
@ -1415,7 +1468,28 @@ gpgsm_decrypt (ctrl_t ctrl, int in_fd, estream_t out_fp)
}
}
}
else if (stopreason == KSBA_SR_READY)
{
if (dfparm.mode == GCRY_CIPHER_MODE_GCM)
{
char *authtag;
size_t authtaglen;
rc = ksba_cms_get_message_digest (cms, 0, &authtag, &authtaglen);
if (rc)
{
log_error ("error getting authtag: %s\n", gpg_strerror (rc));
goto leave;
}
if (DBG_CRYPTO)
log_printhex (authtag, authtaglen, "Authtag ...:");
rc = gcry_cipher_checktag (dfparm.hd, authtag, authtaglen);
xfree (authtag);
if (rc)
log_error ("data is not authentic: %s\n", gpg_strerror (rc));
goto leave;
}
}
}
while (stopreason != KSBA_SR_READY);