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gpg: Allow decryption of symencr even for non-compliant cipher.

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* g10/decrypt-data.c (decrypt_data): Add arg compliance_error.  Adjust
all callers.  Fail on compliance error only in --require-compliance
mode.  Make sure to return an error if the buffer is missing; actually
that should be an assert.
* g10/mainproc.c (proc_encrypted): Delay printing of the compliance
mode status.  Consult the compliance error now returned by
decrypt_data.
--

The actual case here is that we fail hard if a message has been AEAD
encrypted with one AEAD capable key and also with one passphrase.  In
general the preference system takes care of not using AEAD if one
recipient's key does not support it.  However, if the sender uses her
own AEAD-capable key _and_ a passphrase the message will be AEAD
encrypted.  This change allows to decrypt that anyway along with a
warning message.

Note that this does currently not work in 2.3 due to a non-compliant
libgcrypt.  We will however, backport this to 2.2.
This commit is contained in:
Werner Koch 2022-03-18 11:13:23 +01:00
parent 6d6438a361
commit 8631d4cfe2
No known key found for this signature in database
GPG Key ID: E3FDFF218E45B72B
5 changed files with 47 additions and 18 deletions
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17
g10/decrypt-data.c
View File

@ -214,10 +214,14 @@ aead_checktag (decode_filter_ctx_t dfx, int final, const void *tagbuf)
/****************
* Decrypt the data, specified by ED with the key DEK.
* Decrypt the data, specified by ED with the key DEK. On return
* COMPLIANCE_ERROR is set to true iff the decryption can claim that
* it was compliant in the current mode; otherwise this flag is set to
* false.
*/
int
decrypt_data (ctrl_t ctrl, void *procctx, PKT_encrypted *ed, DEK *dek)
decrypt_data (ctrl_t ctrl, void *procctx, PKT_encrypted *ed, DEK *dek,
int *compliance_error)
{
decode_filter_ctx_t dfx;
enum gcry_cipher_modes ciphermode;
@ -228,6 +232,8 @@ decrypt_data (ctrl_t ctrl, void *procctx, PKT_encrypted *ed, DEK *dek)
unsigned int blocksize;
unsigned int nprefix;
*compliance_error = 0;
dfx = xtrycalloc (1, sizeof *dfx);
if (!dfx)
return gpg_error_from_syserror ();
@ -261,9 +267,15 @@ decrypt_data (ctrl_t ctrl, void *procctx, PKT_encrypted *ed, DEK *dek)
log_error (_("cipher algorithm '%s' may not be used in %s mode\n"),
openpgp_cipher_algo_name (dek->algo),
gnupg_compliance_option_string (opt.compliance));
*compliance_error = 1;
if (opt.flags.require_compliance)
{
/* We fail early in this case because it does not make sense
* to first decrypt everything. */
rc = gpg_error (GPG_ERR_CIPHER_ALGO);
goto leave;
}
}
write_status_printf (STATUS_DECRYPTION_INFO, "%d %d %d",
ed->mdc_method, dek->algo, ed->aead_algo);
@ -424,6 +436,7 @@ decrypt_data (ctrl_t ctrl, void *procctx, PKT_encrypted *ed, DEK *dek)
if (!ed->buf)
{
log_error (_("problem handling encrypted packet\n"));
rc = gpg_error (GPG_ERR_INV_PACKET);
goto leave;
}

4
g10/gpgv.c
View File

@ -544,12 +544,14 @@ get_override_session_key (DEK *dek, const char *string)
/* Stub: */
int
decrypt_data (ctrl_t ctrl, void *procctx, PKT_encrypted *ed, DEK *dek)
decrypt_data (ctrl_t ctrl, void *procctx, PKT_encrypted *ed, DEK *dek,
int *compliance_error)
{
(void)ctrl;
(void)procctx;
(void)ed;
(void)dek;
(void)compliance_error;
return GPG_ERR_GENERAL;
}

29
g10/mainproc.c
View File

@ -722,16 +722,17 @@ proc_encrypted (CTX c, PACKET *pkt)
xfree (pk);
if (compliant)
{
write_status_strings (STATUS_DECRYPTION_COMPLIANCE_MODE,
gnupg_status_compliance_flag (CO_DE_VS),
NULL);
compliance_de_vs |= 1;
}
}
if (!result)
result = decrypt_data (c->ctrl, c, pkt->pkt.encrypted, c->dek );
{
int compl_error;
result = decrypt_data (c->ctrl, c, pkt->pkt.encrypted, c->dek,
&compl_error);
if (!result && !compl_error)
compliance_de_vs |= 2;
}
/* Trigger the deferred error. */
if (!result && early_plaintext)
@ -784,12 +785,12 @@ proc_encrypted (CTX c, PACKET *pkt)
if (pkt->pkt.encrypted->aead_algo)
{
write_status (STATUS_GOODMDC);
compliance_de_vs |= 2;
compliance_de_vs |= 4;
}
else if (pkt->pkt.encrypted->mdc_method && !result)
{
write_status (STATUS_GOODMDC);
compliance_de_vs |= 2;
compliance_de_vs |= 4;
}
else
log_info (_("WARNING: message was not integrity protected\n"));
@ -821,6 +822,16 @@ proc_encrypted (CTX c, PACKET *pkt)
* ways to specify the session key (symmmetric and PK). */
}
/* If we concluded that the decryption was compliant, issue a
* compliance status before the thed end of decryption status. */
if (compliance_de_vs == (4|2|1))
{
write_status_strings (STATUS_DECRYPTION_COMPLIANCE_MODE,
gnupg_status_compliance_flag (CO_DE_VS),
NULL);
}
xfree (c->dek);
c->dek = NULL;
free_packet (pkt, NULL);
@ -837,7 +848,7 @@ proc_encrypted (CTX c, PACKET *pkt)
* de-vs compliance mode by just looking at the exit status. */
if (opt.flags.require_compliance
&& opt.compliance == CO_DE_VS
&& compliance_de_vs != (2|1))
&& compliance_de_vs != (4|2|1))
{
log_error (_("operation forced to fail due to"
" unfulfilled compliance rules\n"));

5
g10/packet.h
View File

@ -914,8 +914,9 @@ gpg_error_t get_override_session_key (DEK *dek, const char *string);
int handle_compressed (ctrl_t ctrl, void *ctx, PKT_compressed *cd,
int (*callback)(iobuf_t, void *), void *passthru );
/*-- encr-data.c --*/
int decrypt_data (ctrl_t ctrl, void *ctx, PKT_encrypted *ed, DEK *dek );
/*-- decrypt-data.c --*/
int decrypt_data (ctrl_t ctrl, void *ctx, PKT_encrypted *ed, DEK *dek,
int *compliance_error);
/*-- plaintext.c --*/
gpg_error_t get_output_file (const byte *embedded_name, int embedded_namelen,

4
g10/test-stubs.c
View File

@ -305,12 +305,14 @@ get_override_session_key (DEK *dek, const char *string)
/* Stub: */
int
decrypt_data (ctrl_t ctrl, void *procctx, PKT_encrypted *ed, DEK *dek)
decrypt_data (ctrl_t ctrl, void *procctx, PKT_encrypted *ed, DEK *dek,
int *compliance_error)
{
(void)ctrl;
(void)procctx;
(void)ed;
(void)dek;
(void)compliance_error;
return GPG_ERR_GENERAL;
}