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gnupg/g10/pubkey-enc.c
Werner Koch 4e117f206b
gpg,sm: Error out on compliance mismatch while decrypting. 
* g10/pubkey-enc.c (get_session_key): Bail out if the algo is not
allowed in the current compliance mode.
* sm/decrypt.c (gpgsm_decrypt): Ditto.
--

The idea here is that the owner of the key created a non-compliant key
and later receives a mail encrypted to that key.  The sender should
have checked this key too but we can't guarantee that.  By hard
failing here the owner of the key will notice that he had created a
non-compliant key and thus has a chance to generate a new compliant
key.  In case the compliant criteria changes and the owner wants to
decrypt an old message he can still switch gpg to another compliant
mode.

Fixes-commit: a0d0cbee76
GnuPG-bug-id: 3308
Signed-off-by: Werner Koch <wk@gnupg.org>
2017-08-01 08:41:47 +02:00

487 lines
14 KiB
C
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/* pubkey-enc.c - Process a public key encoded packet.
* Copyright (C) 1998, 1999, 2000, 2001, 2002, 2006, 2009,
* 2010 Free Software Foundation, Inc.
*
* This file is part of GnuPG.
*
* GnuPG is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 3 of the License, or
* (at your option) any later version.
*
* GnuPG 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, see <https://www.gnu.org/licenses/>.
*/
#include <config.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "gpg.h"
#include "../common/util.h"
#include "packet.h"
#include "keydb.h"
#include "trustdb.h"
#include "../common/status.h"
#include "options.h"
#include "main.h"
#include "../common/i18n.h"
#include "pkglue.h"
#include "call-agent.h"
#include "../common/host2net.h"
#include "../common/compliance.h"
static gpg_error_t get_it (ctrl_t ctrl, PKT_pubkey_enc *k,
DEK *dek, PKT_public_key *sk, u32 *keyid);
/* Check that the given algo is mentioned in one of the valid user-ids. */
static int
is_algo_in_prefs (kbnode_t keyblock, preftype_t type, int algo)
{
kbnode_t k;
for (k = keyblock; k; k = k->next)
{
if (k->pkt->pkttype == PKT_USER_ID)
{
PKT_user_id *uid = k->pkt->pkt.user_id;
prefitem_t *prefs = uid->prefs;
if (uid->created && prefs && !uid->flags.revoked && !uid->flags.expired)
{
for (; prefs->type; prefs++)
if (prefs->type == type && prefs->value == algo)
return 1;
}
}
}
return 0;
}
/*
* Get the session key from a pubkey enc packet and return it in DEK,
* which should have been allocated in secure memory by the caller.
*/
gpg_error_t
get_session_key (ctrl_t ctrl, PKT_pubkey_enc * k, DEK * dek)
{
PKT_public_key *sk = NULL;
int rc;
if (DBG_CLOCK)
log_clock ("get_session_key enter");
rc = openpgp_pk_test_algo2 (k->pubkey_algo, PUBKEY_USAGE_ENC);
if (rc)
goto leave;
if ((k->keyid[0] || k->keyid[1]) && !opt.try_all_secrets)
{
sk = xmalloc_clear (sizeof *sk);
sk->pubkey_algo = k->pubkey_algo; /* We want a pubkey with this algo. */
if (!(rc = get_seckey (ctrl, sk, k->keyid)))
{
/* Check compliance. */
if (! gnupg_pk_is_allowed (opt.compliance, PK_USE_DECRYPTION,
sk->pubkey_algo,
sk->pkey, nbits_from_pk (sk), NULL))
{
log_info (_("key %s is not suitable for decryption"
" in %s mode\n"),
keystr_from_pk (sk),
gnupg_compliance_option_string (opt.compliance));
rc = gpg_error (GPG_ERR_PUBKEY_ALGO);
}
else
rc = get_it (ctrl, k, dek, sk, k->keyid);
}
}
else if (opt.skip_hidden_recipients)
rc = gpg_error (GPG_ERR_NO_SECKEY);
else /* Anonymous receiver: Try all available secret keys. */
{
void *enum_context = NULL;
u32 keyid[2];
for (;;)
{
free_public_key (sk);
sk = xmalloc_clear (sizeof *sk);
rc = enum_secret_keys (ctrl, &enum_context, sk);
if (rc)
{
rc = GPG_ERR_NO_SECKEY;
break;
}
if (sk->pubkey_algo != k->pubkey_algo)
continue;
if (!(sk->pubkey_usage & PUBKEY_USAGE_ENC))
continue;
keyid_from_pk (sk, keyid);
if (!opt.quiet)
log_info (_("anonymous recipient; trying secret key %s ...\n"),
keystr (keyid));
/* Check compliance. */
if (! gnupg_pk_is_allowed (opt.compliance, PK_USE_DECRYPTION,
sk->pubkey_algo,
sk->pkey, nbits_from_pk (sk), NULL))
{
log_info (_("key %s is not suitable for decryption"
" in %s mode\n"),
keystr_from_pk (sk),
gnupg_compliance_option_string (opt.compliance));
continue;
}
rc = get_it (ctrl, k, dek, sk, keyid);
if (!rc)
{
if (!opt.quiet)
log_info (_("okay, we are the anonymous recipient.\n"));
break;
}
else if (gpg_err_code (rc) == GPG_ERR_FULLY_CANCELED)
break; /* Don't try any more secret keys. */
}
enum_secret_keys (ctrl, &enum_context, NULL); /* free context */
}
leave:
free_public_key (sk);
if (DBG_CLOCK)
log_clock ("get_session_key leave");
return rc;
}
static gpg_error_t
get_it (ctrl_t ctrl,
PKT_pubkey_enc *enc, DEK *dek, PKT_public_key *sk, u32 *keyid)
{
gpg_error_t err;
byte *frame = NULL;
unsigned int n;
size_t nframe;
u16 csum, csum2;
int padding;
gcry_sexp_t s_data;
char *desc;
char *keygrip;
byte fp[MAX_FINGERPRINT_LEN];
size_t fpn;
if (DBG_CLOCK)
log_clock ("decryption start");
/* Get the keygrip. */
err = hexkeygrip_from_pk (sk, &keygrip);
if (err)
goto leave;
/* Convert the data to an S-expression. */
if (sk->pubkey_algo == PUBKEY_ALGO_ELGAMAL
|| sk->pubkey_algo == PUBKEY_ALGO_ELGAMAL_E)
{
if (!enc->data[0] || !enc->data[1])
err = gpg_error (GPG_ERR_BAD_MPI);
else
err = gcry_sexp_build (&s_data, NULL, "(enc-val(elg(a%m)(b%m)))",
enc->data[0], enc->data[1]);
}
else if (sk->pubkey_algo == PUBKEY_ALGO_RSA
|| sk->pubkey_algo == PUBKEY_ALGO_RSA_E)
{
if (!enc->data[0])
err = gpg_error (GPG_ERR_BAD_MPI);
else
err = gcry_sexp_build (&s_data, NULL, "(enc-val(rsa(a%m)))",
enc->data[0]);
}
else if (sk->pubkey_algo == PUBKEY_ALGO_ECDH)
{
if (!enc->data[0] || !enc->data[1])
err = gpg_error (GPG_ERR_BAD_MPI);
else
err = gcry_sexp_build (&s_data, NULL, "(enc-val(ecdh(s%m)(e%m)))",
enc->data[1], enc->data[0]);
}
else
err = gpg_error (GPG_ERR_BUG);
if (err)
goto leave;
if (sk->pubkey_algo == PUBKEY_ALGO_ECDH)
{
fingerprint_from_pk (sk, fp, &fpn);
log_assert (fpn == 20);
}
/* Decrypt. */
desc = gpg_format_keydesc (ctrl, sk, FORMAT_KEYDESC_NORMAL, 1);
err = agent_pkdecrypt (NULL, keygrip,
desc, sk->keyid, sk->main_keyid, sk->pubkey_algo,
s_data, &frame, &nframe, &padding);
xfree (desc);
gcry_sexp_release (s_data);
if (err)
goto leave;
/* Now get the DEK (data encryption key) from the frame
*
* Old versions encode the DEK in this format (msb is left):
*
* 0 1 DEK(16 bytes) CSUM(2 bytes) 0 RND(n bytes) 2
*
* Later versions encode the DEK like this:
*
* 0 2 RND(n bytes) 0 A DEK(k bytes) CSUM(2 bytes)
*
* (mpi_get_buffer already removed the leading zero).
*
* RND are non-zero randow bytes.
* A is the cipher algorithm
* DEK is the encryption key (session key) with length k
* CSUM
*/
if (DBG_CRYPTO)
log_printhex ("DEK frame:", frame, nframe);
n = 0;
if (sk->pubkey_algo == PUBKEY_ALGO_ECDH)
{
gcry_mpi_t shared_mpi;
gcry_mpi_t decoded;
/* At the beginning the frame are the bytes of shared point MPI. */
err = gcry_mpi_scan (&shared_mpi, GCRYMPI_FMT_USG, frame, nframe, NULL);
if (err)
{
err = gpg_error (GPG_ERR_WRONG_SECKEY);
goto leave;
}
err = pk_ecdh_decrypt (&decoded, fp, enc->data[1]/*encr data as an MPI*/,
shared_mpi, sk->pkey);
mpi_release (shared_mpi);
if(err)
goto leave;
xfree (frame);
err = gcry_mpi_aprint (GCRYMPI_FMT_USG, &frame, &nframe, decoded);
mpi_release (decoded);
if (err)
goto leave;
/* Now the frame are the bytes decrypted but padded session key. */
/* Allow double padding for the benefit of DEK size concealment.
Higher than this is wasteful. */
if (!nframe || frame[nframe-1] > 8*2 || nframe <= 8
|| frame[nframe-1] > nframe)
{
err = gpg_error (GPG_ERR_WRONG_SECKEY);
goto leave;
}
nframe -= frame[nframe-1]; /* Remove padding. */
log_assert (!n); /* (used just below) */
}
else
{
if (padding)
{
if (n + 7 > nframe)
{
err = gpg_error (GPG_ERR_WRONG_SECKEY);
goto leave;
}
if (frame[n] == 1 && frame[nframe - 1] == 2)
{
log_info (_("old encoding of the DEK is not supported\n"));
err = gpg_error (GPG_ERR_CIPHER_ALGO);
goto leave;
}
if (frame[n] != 2) /* Something went wrong. */
{
err = gpg_error (GPG_ERR_WRONG_SECKEY);
goto leave;
}
for (n++; n < nframe && frame[n]; n++) /* Skip the random bytes. */
;
n++; /* Skip the zero byte. */
}
}
if (n + 4 > nframe)
{
err = gpg_error (GPG_ERR_WRONG_SECKEY);
goto leave;
}
dek->keylen = nframe - (n + 1) - 2;
dek->algo = frame[n++];
err = openpgp_cipher_test_algo (dek->algo);
if (err)
{
if (!opt.quiet && gpg_err_code (err) == GPG_ERR_CIPHER_ALGO)
{
log_info (_("cipher algorithm %d%s is unknown or disabled\n"),
dek->algo,
dek->algo == CIPHER_ALGO_IDEA ? " (IDEA)" : "");
}
dek->algo = 0;
goto leave;
}
if (dek->keylen != openpgp_cipher_get_algo_keylen (dek->algo))
{
err = gpg_error (GPG_ERR_WRONG_SECKEY);
goto leave;
}
/* Copy the key to DEK and compare the checksum. */
csum = buf16_to_u16 (frame+nframe-2);
memcpy (dek->key, frame + n, dek->keylen);
for (csum2 = 0, n = 0; n < dek->keylen; n++)
csum2 += dek->key[n];
if (csum != csum2)
{
err = gpg_error (GPG_ERR_WRONG_SECKEY);
goto leave;
}
if (DBG_CLOCK)
log_clock ("decryption ready");
if (DBG_CRYPTO)
log_printhex ("DEK is:", dek->key, dek->keylen);
/* Check that the algo is in the preferences and whether it has
* expired. Also print a status line with the key's fingerprint. */
{
PKT_public_key *pk = NULL;
PKT_public_key *mainpk = NULL;
KBNODE pkb = get_pubkeyblock (ctrl, keyid);
if (!pkb)
{
err = -1;
log_error ("oops: public key not found for preference check\n");
}
else if (pkb->pkt->pkt.public_key->selfsigversion > 3
&& dek->algo != CIPHER_ALGO_3DES
&& !opt.quiet
&& !is_algo_in_prefs (pkb, PREFTYPE_SYM, dek->algo))
log_info (_("WARNING: cipher algorithm %s not found in recipient"
" preferences\n"), openpgp_cipher_algo_name (dek->algo));
if (!err)
{
kbnode_t k;
int first = 1;
for (k = pkb; k; k = k->next)
{
if (k->pkt->pkttype == PKT_PUBLIC_KEY
|| k->pkt->pkttype == PKT_PUBLIC_SUBKEY)
{
u32 aki[2];
if (first)
{
first = 0;
mainpk = k->pkt->pkt.public_key;
}
keyid_from_pk (k->pkt->pkt.public_key, aki);
if (aki[0] == keyid[0] && aki[1] == keyid[1])
{
pk = k->pkt->pkt.public_key;
break;
}
}
}
if (!pk)
BUG ();
if (pk->expiredate && pk->expiredate <= make_timestamp ())
{
log_info (_("Note: secret key %s expired at %s\n"),
keystr (keyid), asctimestamp (pk->expiredate));
}
}
if (pk && pk->flags.revoked)
{
log_info (_("Note: key has been revoked"));
log_printf ("\n");
show_revocation_reason (ctrl, pk, 1);
}
if (is_status_enabled () && pk && mainpk)
{
char pkhex[MAX_FINGERPRINT_LEN*2+1];
char mainpkhex[MAX_FINGERPRINT_LEN*2+1];
hexfingerprint (pk, pkhex, sizeof pkhex);
hexfingerprint (mainpk, mainpkhex, sizeof mainpkhex);
/* Note that we do not want to create a trustdb just for
* getting the ownertrust: If there is no trustdb there can't
* be ulitmately trusted key anyway and thus the ownertrust
* value is irrelevant. */
write_status_printf (STATUS_DECRYPTION_KEY, "%s %s %c",
pkhex, mainpkhex,
get_ownertrust_info (ctrl, mainpk, 1));
}
release_kbnode (pkb);
err = 0;
}
leave:
xfree (frame);
xfree (keygrip);
return err;
}
/*
* Get the session key from the given string.
* String is supposed to be formatted as this:
* <algo-id>:<even-number-of-hex-digits>
*/
gpg_error_t
get_override_session_key (DEK *dek, const char *string)
{
const char *s;
int i;
if (!string)
return GPG_ERR_BAD_KEY;
dek->algo = atoi (string);
if (dek->algo < 1)
return GPG_ERR_BAD_KEY;
if (!(s = strchr (string, ':')))
return GPG_ERR_BAD_KEY;
s++;
for (i = 0; i < DIM (dek->key) && *s; i++, s += 2)
{
int c = hextobyte (s);
if (c == -1)
return GPG_ERR_BAD_KEY;
dek->key[i] = c;
}
if (*s)
return GPG_ERR_BAD_KEY;
dek->keylen = i;
return 0;
}
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