/* decrypt.c - Decrypt function.
* Copyright (C) 2000 Werner Koch (dd9jn)
* Copyright (C) 2001, 2002, 2003, 2004, 2017 g10 Code GmbH
*
* This file is part of GPGME.
*
* GPGME is free software; you can redistribute it and/or modify it
* under the terms of the GNU Lesser General Public License as
* published by the Free Software Foundation; either version 2.1 of
* the License, or (at your option) any later version.
*
* GPGME is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this program; if not, see <https://gnu.org/licenses/>.
* SPDX-License-Identifier: LGPL-2.1-or-later
*/
#if HAVE_CONFIG_H
#include <config.h>
#endif
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <assert.h>
#include "debug.h"
#include "gpgme.h"
#include "util.h"
#include "context.h"
#include "ops.h"
#include "data.h"
typedef struct
{
struct _gpgme_op_decrypt_result result;
/* The error code from a FAILURE status line or 0. */
gpg_error_t failure_code;
int okay;
/* A flag telling that the a decryption failed and two optional error
* codes to further specify the failure for public key decryption and
* symmetric decryption. */
int failed;
gpg_error_t pkdecrypt_failed;
gpg_error_t symdecrypt_failed;
/* At least one secret key is not available. gpg issues NO_SECKEY
* status lines for each key the message has been encrypted to but
* that secret key is not available. This can't be done for hidden
* recipients, though. We track it here to allow for a better error
* message than the general DECRYPTION_FAILED. */
int any_no_seckey;
/* If the engine emits a DECRYPTION_INFO status and that does not
* indicate that an integrity protection mode is active, this flag
* is set. */
int not_integrity_protected;
/* The error code from the first ERROR line. This is in some cases
* used to return a better matching error code to the caller. */
gpg_error_t first_status_error;
/* A pointer to the next pointer of the last recipient in the list.
This makes appending new invalid signers painless while
preserving the order. */
gpgme_recipient_t *last_recipient_p;
/* The data object serial number of the plaintext. */
uint64_t plaintext_dserial;
} *op_data_t;
static void
release_op_data (void *hook)
{
op_data_t opd = (op_data_t) hook;
gpgme_recipient_t recipient = opd->result.recipients;
free (opd->result.unsupported_algorithm);
free (opd->result.file_name);
free (opd->result.session_key);
free (opd->result.symkey_algo);
while (recipient)
{
gpgme_recipient_t next = recipient->next;
free (recipient);
recipient = next;
}
}
gpgme_decrypt_result_t
gpgme_op_decrypt_result (gpgme_ctx_t ctx)
{
void *hook;
op_data_t opd;
gpgme_error_t err;
TRACE_BEG (DEBUG_CTX, "gpgme_op_decrypt_result", ctx, "");
ctx->ignore_mdc_error = 0; /* Always reset this flag. */
err = _gpgme_op_data_lookup (ctx, OPDATA_DECRYPT, &hook, -1, NULL);
opd = hook;
if (err || !opd)
{
TRACE_SUC ("result=(null)");
return NULL;
}
/* Make sure that SYMKEY_ALGO has a value. */
if (!opd->result.symkey_algo)
{
opd->result.symkey_algo = strdup ("?.?");
if (!opd->result.symkey_algo)
{
TRACE_SUC ("result=(null)");
return NULL;
}
}
if (_gpgme_debug_trace ())
{
gpgme_recipient_t rcp;
if (opd->result.unsupported_algorithm)
{
TRACE_LOG ("result: unsupported_algorithm: %s",
opd->result.unsupported_algorithm);
}
if (opd->result.wrong_key_usage)
{
TRACE_LOG ("result: wrong key usage");
}
rcp = opd->result.recipients;
while (rcp)
{
TRACE_LOG ("result: recipient: keyid=%s, pubkey_algo=%i, "
"status=%s", rcp->keyid, rcp->pubkey_algo,
gpg_strerror (rcp->status));
rcp = rcp->next;
}
if (opd->result.file_name)
{
TRACE_LOG ("result: original file name: %s", opd->result.file_name);
}
}
TRACE_SUC ("result=%p", &opd->result);
return &opd->result;
}
/* Parse the ARGS of an error status line and record some error
* conditions at OPD. Returns 0 on success. */
static gpgme_error_t
parse_status_error (char *args, op_data_t opd)
{
gpgme_error_t err;
char *field[3];
int nfields;
char *args2;
if (!args)
return trace_gpg_error (GPG_ERR_INV_ENGINE);
args2 = strdup (args); /* Split modifies the input string. */
nfields = _gpgme_split_fields (args2, field, DIM (field));
if (nfields < 1)
{
free (args2);
return trace_gpg_error (GPG_ERR_INV_ENGINE); /* Required arg missing. */
}
err = nfields < 2 ? 0 : atoi (field[1]);
if (!strcmp (field[0], "decrypt.algorithm"))
{
if (gpg_err_code (err) == GPG_ERR_UNSUPPORTED_ALGORITHM
&& nfields > 2
&& strcmp (field[2], "?"))
{
opd->result.unsupported_algorithm = strdup (field[2]);
if (!opd->result.unsupported_algorithm)
{
free (args2);
return gpg_error_from_syserror ();
}
}
}
else if (!strcmp (field[0], "decrypt.keyusage"))
{
if (gpg_err_code (err) == GPG_ERR_WRONG_KEY_USAGE)
opd->result.wrong_key_usage = 1;
}
else if (!strcmp (field[0], "pkdecrypt_failed"))
{
switch (gpg_err_code (err))
{
case GPG_ERR_CANCELED:
case GPG_ERR_FULLY_CANCELED:
/* It is better to return with a cancel error code than the
* general decryption failed error code. */
opd->pkdecrypt_failed = gpg_err_make (gpg_err_source (err),
GPG_ERR_CANCELED);
break;
case GPG_ERR_BAD_PASSPHRASE:
/* A bad passphrase is severe enough that we return this
* error code. */
opd->pkdecrypt_failed = err;
break;
default:
/* For now all other error codes are ignored and the
* standard DECRYPT_FAILED is returned. */
break;
}
}
else if (!strcmp (field[0], "nomdc_with_legacy_cipher"))
{
opd->result.legacy_cipher_nomdc = 1;
opd->not_integrity_protected = 1;
}
else if (!strcmp (field[0], "symkey_decrypt.maybe_error"))
{
switch (gpg_err_code (err))
{
case GPG_ERR_BAD_PASSPHRASE:
/* A bad passphrase is severe enough that we return this
* error code. */
opd->symdecrypt_failed = err;
break;
default:
/* For now all other error codes are ignored and the
* standard DECRYPT_FAILED is returned. */
break;
}
}
/* Record the first error code. */
if (err && !opd->first_status_error)
opd->first_status_error = err;
free (args2);
return 0;
}
static gpgme_error_t
parse_enc_to (char *args, gpgme_recipient_t *recp, gpgme_protocol_t protocol)
{
gpgme_recipient_t rec;
char *tail;
int i;
rec = malloc (sizeof (*rec));
if (!rec)
return gpg_error_from_syserror ();
rec->next = NULL;
rec->keyid = rec->_keyid;
rec->status = 0;
for (i = 0; i < sizeof (rec->_keyid) - 1; i++)
{
if (args[i] == '\0' || args[i] == ' ')
break;
rec->_keyid[i] = args[i];
}
rec->_keyid[i] = '\0';
args = &args[i];
if (*args != '\0' && *args != ' ')
{
free (rec);
return trace_gpg_error (GPG_ERR_INV_ENGINE);
}
while (*args == ' ')
args++;
if (*args)
{
gpg_err_set_errno (0);
rec->pubkey_algo = _gpgme_map_pk_algo (strtol (args, &tail, 0), protocol);
if (errno || args == tail || *tail != ' ')
{
/* The crypto backend does not behave. */
free (rec);
return trace_gpg_error (GPG_ERR_INV_ENGINE);
}
}
/* FIXME: The key length is always 0 right now, so no need to parse
it. */
*recp = rec;
return 0;
}
/* Parse the ARGS of a
* DECRYPTION_INFO <mdc_method> <sym_algo> [<aead_algo>]
* status. Returns 0 on success and updates the OPD.
*/
static gpgme_error_t
parse_decryption_info (char *args, op_data_t opd, gpgme_protocol_t protocol)
{
char *field[3];
int nfields;
char *args2;
int mdc, aead_algo;
const char *algostr, *modestr;
if (!args)
return trace_gpg_error (GPG_ERR_INV_ENGINE);
args2 = strdup (args); /* Split modifies the input string. */
nfields = _gpgme_split_fields (args2, field, DIM (field));
if (nfields < 2)
{
free (args2);
return trace_gpg_error (GPG_ERR_INV_ENGINE); /* Required arg missing. */
}
mdc = atoi (field[0]);
algostr = _gpgme_cipher_algo_name (atoi (field[1]), protocol);
aead_algo = nfields < 3? 0 : atoi (field[2]);
modestr = _gpgme_cipher_mode_name (aead_algo, protocol);
free (args2);
free (opd->result.symkey_algo);
if (!aead_algo && mdc != 2)
opd->result.symkey_algo = _gpgme_strconcat (algostr, ".PGPCFB", NULL);
else
opd->result.symkey_algo = _gpgme_strconcat (algostr, ".", modestr, NULL);
if (!opd->result.symkey_algo)
return gpg_error_from_syserror ();
if (!mdc && !aead_algo)
opd->not_integrity_protected = 1;
return 0;
}
gpgme_error_t
_gpgme_decrypt_status_handler (void *priv, gpgme_status_code_t code,
char *args)
{
gpgme_ctx_t ctx = (gpgme_ctx_t) priv;
gpgme_error_t err;
void *hook;
op_data_t opd;
err = _gpgme_passphrase_status_handler (priv, code, args);
if (err)
return err;
err = _gpgme_op_data_lookup (ctx, OPDATA_DECRYPT, &hook, -1, NULL);
opd = hook;
if (err)
return err;
switch (code)
{
case GPGME_STATUS_FAILURE:
opd->failure_code = _gpgme_parse_failure (args);
break;
case GPGME_STATUS_EOF:
/* We force an encryption failure if we know that integrity
* protection is missing. For modern version of gpg using
* modern cipher algorithms this is not required because gpg
* will issue a failure anyway. However older gpg versions emit
* only a warning.
* Fixme: These error values should probably be attributed to
* the underlying crypto engine (as error source). */
if (opd->failed)
{
/* This comes from a specialized ERROR status line. */
if (opd->pkdecrypt_failed)
return opd->pkdecrypt_failed;
if (opd->symdecrypt_failed)
return opd->symdecrypt_failed;
/* For an integrity failure return just DECRYPTION_FAILED;
* the actual cause can be taken from an already set
* decryption result flag. */
if ((opd->not_integrity_protected && !ctx->ignore_mdc_error))
return gpg_error (GPG_ERR_DECRYPT_FAILED);
/* If we have any other ERROR code we prefer that over
* NO_SECKEY because it is probably the better matching
* code. For example a garbled message with multiple
* plaintext will return BAD_DATA here but may also have
* indicated a NO_SECKEY. */
if (opd->first_status_error)
return opd->first_status_error;
/* No secret key is pretty common reason. */
if (opd->any_no_seckey)
return gpg_error (GPG_ERR_NO_SECKEY);
/* Generic decryption failed error code. */
return gpg_error (GPG_ERR_DECRYPT_FAILED);
}
else if (!opd->okay)
{
/* No data was found. */
return gpg_error (GPG_ERR_NO_DATA);
}
else if (opd->failure_code)
{
/* The engine returned failure code at program exit. */
return opd->failure_code;
}
break;
case GPGME_STATUS_DECRYPTION_INFO:
err = parse_decryption_info (args, opd, ctx->protocol);
if (err)
return err;
break;
case GPGME_STATUS_DECRYPTION_OKAY:
opd->okay = 1;
break;
case GPGME_STATUS_DECRYPTION_FAILED:
opd->failed = 1;
/* Tell the data object that it shall not return any data. We
* use the serial number because the data object may be owned by
* another thread. We also don't check for an error because it
* is possible that the data object has already been destroyed
* and we are then not interested in returning an error. */
if (!ctx->ignore_mdc_error)
_gpgme_data_set_prop (NULL, opd->plaintext_dserial,
DATA_PROP_BLANKOUT, 1);
break;
case GPGME_STATUS_ERROR:
/* Note that this is an informational status code which should
* not lead to an error return unless it is something not
* related to the backend. However, it is used to return a
* better matching final error code. */
err = parse_status_error (args, opd);
if (err)
return err;
break;
case GPGME_STATUS_ENC_TO:
err = parse_enc_to (args, opd->last_recipient_p, ctx->protocol);
if (err)
return err;
opd->last_recipient_p = &(*opd->last_recipient_p)->next;
break;
case GPGME_STATUS_SESSION_KEY:
if (opd->result.session_key)
free (opd->result.session_key);
opd->result.session_key = strdup(args);
break;
case GPGME_STATUS_NO_SECKEY:
{
gpgme_recipient_t rec = opd->result.recipients;
while (rec)
{
if (!strcmp (rec->keyid, args))
{
rec->status = gpg_error (GPG_ERR_NO_SECKEY);
break;
}
rec = rec->next;
}
/* FIXME: Is this ok? */
if (!rec)
return trace_gpg_error (GPG_ERR_INV_ENGINE);
opd->any_no_seckey = 1;
}
break;
case GPGME_STATUS_PLAINTEXT:
{
int mime = 0;
err = _gpgme_parse_plaintext (args, &opd->result.file_name, &mime);
if (err)
return err;
opd->result.is_mime = !!mime;
}
break;
case GPGME_STATUS_INQUIRE_MAXLEN:
if (ctx->status_cb && !ctx->full_status)
{
err = ctx->status_cb (ctx->status_cb_value, "INQUIRE_MAXLEN", args);
if (err)
return err;
}
break;
case GPGME_STATUS_DECRYPTION_COMPLIANCE_MODE:
PARSE_COMPLIANCE_FLAGS (args, &opd->result);
break;
default:
break;
}
return 0;
}
static gpgme_error_t
decrypt_status_handler (void *priv, gpgme_status_code_t code, char *args)
{
gpgme_error_t err;
err = _gpgme_progress_status_handler (priv, code, args);
if (!err)
err = _gpgme_decrypt_status_handler (priv, code, args);
return err;
}
gpgme_error_t
_gpgme_op_decrypt_init_result (gpgme_ctx_t ctx, gpgme_data_t plaintext)
{
gpgme_error_t err;
void *hook;
op_data_t opd;
err = _gpgme_op_data_lookup (ctx, OPDATA_DECRYPT, &hook,
sizeof (*opd), release_op_data);
opd = hook;
if (err)
return err;
opd->last_recipient_p = &opd->result.recipients;
opd->plaintext_dserial = _gpgme_data_get_dserial (plaintext);
return 0;
}
gpgme_error_t
_gpgme_decrypt_start (gpgme_ctx_t ctx, int synchronous,
gpgme_decrypt_flags_t flags,
gpgme_data_t cipher, gpgme_data_t plain)
{
gpgme_error_t err;
assert (!(flags & GPGME_DECRYPT_VERIFY));
err = _gpgme_op_reset (ctx, synchronous);
if (err)
return err;
err = _gpgme_op_decrypt_init_result (ctx, plain);
if (err)
return err;
if (!cipher)
return gpg_error (GPG_ERR_NO_DATA);
if (!plain)
return gpg_error (GPG_ERR_INV_VALUE);
if (err)
return err;
if (ctx->passphrase_cb)
{
err = _gpgme_engine_set_command_handler
(ctx->engine, _gpgme_passphrase_command_handler, ctx);
if (err)
return err;
}
_gpgme_engine_set_status_handler (ctx->engine, decrypt_status_handler, ctx);
return _gpgme_engine_op_decrypt (ctx->engine,
flags,
cipher, plain,
ctx->export_session_keys,
ctx->override_session_key,
ctx->auto_key_retrieve);
}
gpgme_error_t
gpgme_op_decrypt_start (gpgme_ctx_t ctx, gpgme_data_t cipher,
gpgme_data_t plain)
{
gpgme_error_t err;
TRACE_BEG (DEBUG_CTX, "gpgme_op_decrypt_start", ctx,
"cipher=%p, plain=%p", cipher, plain);
if (!ctx)
return TRACE_ERR (gpg_error (GPG_ERR_INV_VALUE));
err = _gpgme_decrypt_start (ctx, 0, 0, cipher, plain);
return TRACE_ERR (err);
}
/* Decrypt ciphertext CIPHER within CTX and store the resulting
plaintext in PLAIN. */
gpgme_error_t
gpgme_op_decrypt (gpgme_ctx_t ctx, gpgme_data_t cipher, gpgme_data_t plain)
{
gpgme_error_t err;
TRACE_BEG (DEBUG_CTX, "gpgme_op_decrypt", ctx,
"cipher=%p, plain=%p", cipher, plain);
if (!ctx)
return TRACE_ERR (gpg_error (GPG_ERR_INV_VALUE));
err = _gpgme_decrypt_start (ctx, 1, 0, cipher, plain);
if (!err)
err = _gpgme_wait_one (ctx);
ctx->ignore_mdc_error = 0; /* Always reset. */
return TRACE_ERR (err);
}