Modern TLS libraries might drop Blowfish by default or distributions
might disable Blowfish in OpenSSL/mbed TLS. We still signal OCC
options with BF-CBC compatible strings. To avoid requiring BF-CBC
for this, special this one usage of BF-CBC enough to avoid a hard
requirement on Blowfish in the default configuration.
This patch is cherry-picked from 79ff3f79 and the missing
ciphername = "none"; has been added in the OCC code.
Signed-off-by: Arne Schwabe <a...@rfc2549.org>
---
src/openvpn/crypto_backend.h | 2 ++
src/openvpn/init.c | 37 +++++++++++++++++++++------
src/openvpn/options.c | 48 +++++++++++++++++++++++++++++++-----
3 files changed, 73 insertions(+), 14 deletions(-)
diff --git a/src/openvpn/crypto_backend.h b/src/openvpn/crypto_backend.h
index a9bb38ed2..aebda3d65 100644
--- a/src/openvpn/crypto_backend.h
+++ b/src/openvpn/crypto_backend.h
@@ -256,6 +256,8 @@ const cipher_kt_t *cipher_kt_get(const char *ciphername);
* The returned name is normalised to the OpenVPN config name in case the
* name differs from the name used by the crypto library.
*
+ * Returns [null-cipher] in case the cipher_kt is NULL.
+ *
* @param cipher_kt Static cipher parameters
*
* @return a statically allocated string describing the cipher.
diff --git a/src/openvpn/init.c b/src/openvpn/init.c
index da4d60afa..f1550e620 100644
--- a/src/openvpn/init.c
+++ b/src/openvpn/init.c
@@ -2764,14 +2764,35 @@ do_init_crypto_tls_c1(struct context *c)
#endif /* if P2MP */
}
- /* Do not warn if we only have BF-CBC in options->ciphername
- * because it is still the default cipher */
- bool warn = !streq(options->ciphername, "BF-CBC")
- || options->enable_ncp_fallback;
- /* Get cipher & hash algorithms */
- init_key_type(&c->c1.ks.key_type, options->ciphername,
options->authname,
- options->keysize, true, warn);
-
+ /*
+ * BF-CBC is allowed to be used only when explicitly configured
+ * as NCP-fallback or when NCP has been disabled or explicitly
+ * allowed in the in ncp_ciphers list.
+ * In all other cases do not attempt to initialize BF-CBC as it
+ * may not even be supported by the underlying SSL library.
+ *
+ * Therefore, the key structure has to be initialized when:
+ * - any non-BF-CBC cipher was selected; or
+ * - BF-CBC is selected and NCP is disabled (explicit request to
+ * use the BF-CBC cipher); or
+ * - BF-CBC is selected, NCP is enabled and fallback is enabled
+ * (BF-CBC will be the fallback).
+ * - BF-CBC is in data-ciphers and we negotiate to use BF-CBC:
+ * If the negotiated cipher and options->ciphername are the
+ * same we do not reinit the cipher
+ *
+ * Note that BF-CBC will still be part of the OCC string to retain
+ * backwards compatibility with older clients.
+ */
+ if (!streq(options->ciphername, "BF-CBC") || !options->ncp_enabled
+ || (options->ncp_enabled && tls_item_in_cipher_list("BF-CBC",
options->ncp_ciphers))
+ || options->enable_ncp_fallback)
+ {
+ /* Do not warn if the if the cipher is used only in OCC */
+ bool warn = !options->ncp_enabled || options->enable_ncp_fallback;
+ init_key_type(&c->c1.ks.key_type, options->ciphername,
options->authname,
+ options->keysize, true, warn);
+ }
/* Initialize PRNG with config-specified digest */
prng_init(options->prng_hash, options->prng_nonce_secret_len);
diff --git a/src/openvpn/options.c b/src/openvpn/options.c
index f6ef02ae8..fd68537b6 100644
--- a/src/openvpn/options.c
+++ b/src/openvpn/options.c
@@ -3681,9 +3681,30 @@ calc_options_string_link_mtu(const struct options *o,
const struct frame *frame)
{
struct frame fake_frame = *frame;
struct key_type fake_kt;
- init_key_type(&fake_kt, o->ciphername, o->authname, o->keysize, true,
- false);
+
frame_remove_from_extra_frame(&fake_frame, crypto_max_overhead());
+
+
+ /* o->ciphername might be BF-CBC even though the underlying SSL library
+ * does not support it. For this reason we workaround this corner case
+ * by pretending to have no encryption enabled and by manually adding
+ * the required packet overhead to the MTU computation.
+ */
+ const char* ciphername = o->ciphername;
+
+ if (strcmp(o->ciphername, "BF-CBC") == 0)
+ {
+ /* none has no overhead, so use this to later add only --auth
+ * overhead */
+
+ /* overhead of BF-CBC: 64 bit block size, 64 bit IV size */
+ frame_add_to_extra_frame(&fake_frame, 64/8 + 64/8);
+ ciphername = "none";
+ }
+
+ init_key_type(&fake_kt, ciphername, o->authname, o->keysize, true,
+ false);
+
crypto_adjust_frame_parameters(&fake_frame, &fake_kt, o->replay,
cipher_kt_mode_ofb_cfb(fake_kt.cipher));
frame_finalize(&fake_frame, o->ce.link_mtu_defined, o->ce.link_mtu,
@@ -3853,18 +3874,33 @@ options_string(const struct options *o,
+ (TLS_SERVER == true)
<= 1);
- init_key_type(&kt, o->ciphername, o->authname, o->keysize, true,
- false);
+ /* Skip resolving BF-CBC to allow SSL libraries without BF-CBC
+ * to work here in the default configuration */
+ const char *ciphername = o->ciphername;
+ int keysize;
+
+ if (strcmp(o->ciphername, "BF-CBC") == 0)
+ {
+ init_key_type(&kt, "none", o->authname, o->keysize, true,
+ false);
+ keysize = 128;
+ }
+ else
+ {
+ init_key_type(&kt, o->ciphername, o->authname, o->keysize, true,
+ false);
+ ciphername = cipher_kt_name(kt.cipher);
+ keysize = kt.cipher_length * 8;
+ }
/* Only announce the cipher to our peer if we are willing to
* support it */
- const char *ciphername = cipher_kt_name(kt.cipher);
if (p2p_nopull || !o->ncp_enabled
|| tls_item_in_cipher_list(ciphername, o->ncp_ciphers))
{
buf_printf(&out, ",cipher %s", ciphername);
}
buf_printf(&out, ",auth %s", md_kt_name(kt.digest));
- buf_printf(&out, ",keysize %d", kt.cipher_length * 8);
+ buf_printf(&out, ",keysize %d", keysize);
if (o->shared_secret_file)
{
buf_printf(&out, ",secret");
--
2.32.0 (Apple Git-132)
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