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gpg: Do not allow old cipher algorithms for encryption.

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* g10/gpg.c: New option --allow-old-cipher-algos.
(set_compliance_option): Set --rfc4880bis explictly to SHA256 and
AES256.  Allow old cipher algos for OpenPGP, rfc4880, and rfc2440.
* g10/options.h (opt): Add flags.allow_old_cipher_algos.
* g10/misc.c (print_sha1_keysig_rejected_note): Always print the note
unless in --quiet mode.
* g10/encrypt.c (setup_symkey): Disallow by default algos with a
blocklengt < 128.
(encrypt_crypt): Ditto.  Fallback by default to AES instead of 3DES.
* g10/pkclist.c (algo_available): Take care of old cipher also.
(select_algo_from_prefs): Use AES as implicit algorithm by default.

* tests/openpgp/defs.scm (create-gpghome): Set allow-old-cipher-algos.
--

GnuPG-bug-id: 3415
This commit is contained in:
Werner Koch 2021-02-10 14:31:34 +01:00
parent 6e730c1881
commit 825dd7220f
No known key found for this signature in database
GPG key ID: E3FDFF218E45B72B
7 changed files with 92 additions and 16 deletions
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35
g10/encrypt.c
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@ -538,6 +538,17 @@ setup_symkey (STRING2KEY **symkey_s2k, DEK **symkey_dek)
int s2kdigest;
defcipher = default_cipher_algo ();
if (openpgp_cipher_blocklen (defcipher) < 16
&& !opt.flags.allow_old_cipher_algos)
{
log_error (_("cipher algorithm '%s' may not be used for encryption\n"),
openpgp_cipher_algo_name (defcipher));
if (!opt.quiet)
log_info (_("(use option \"%s\" to override)\n"),
"--allow-old-cipher-algos");
return gpg_error (GPG_ERR_CIPHER_ALGO);
}
if (!gnupg_cipher_is_allowed (opt.compliance, 1, defcipher,
GCRY_CIPHER_MODE_CFB))
{
@ -741,10 +752,18 @@ encrypt_crypt (ctrl_t ctrl, int filefd, const char *filename,
entry for 3DES, and the pk_list cannot be empty. In this
case, use 3DES anyway as it's the safest choice - perhaps the
v3 key is being used in an OpenPGP implementation and we know
that the implementation behind any v4 key can handle 3DES. */
that the implementation behind any v4 key can handle 3DES.
Note that we do not support v3 keys since version 2.2 so the
above description gives only historical background. */
if (cfx.dek->algo == -1)
{
cfx.dek->algo = CIPHER_ALGO_3DES;
/* If does not make sense to fallback to the rfc4880
* required 3DES if we will reject that algo later. Thus we
* fallback to AES anticipating RFC4880bis rules. */
if (opt.flags.allow_old_cipher_algos)
cfx.dek->algo = CIPHER_ALGO_3DES;
else
cfx.dek->algo = CIPHER_ALGO_AES;
}
/* In case 3DES has been selected, print a warning if any key
@ -770,6 +789,18 @@ encrypt_crypt (ctrl_t ctrl, int filefd, const char *filename,
cfx.dek->algo = opt.def_cipher_algo;
}
if (openpgp_cipher_blocklen (cfx.dek->algo) < 16
&& !opt.flags.allow_old_cipher_algos)
{
log_error (_("cipher algorithm '%s' may not be used for encryption\n"),
openpgp_cipher_algo_name (cfx.dek->algo));
if (!opt.quiet)
log_info (_("(use option \"%s\" to override)\n"),
"--allow-old-cipher-algos");
rc = gpg_error (GPG_ERR_CIPHER_ALGO);
goto leave;
}
/* Check compliance. */
if (! gnupg_cipher_is_allowed (opt.compliance, 1, cfx.dek->algo,
GCRY_CIPHER_MODE_CFB))