As discussed with the development team, we should start moving away from
ciphers with a small block size. For OpenVPN in particular this means
moving away from 64-bit block ciphers, towards 128-bit block ciphers.
This patch makes a start with that by moving ciphers with a block
size < 128 bits to the bottom of the --show-ciphers output, and printing
a warning in the connection phase if such a cipher is used.
While touching this function, improve the output of --show-ciphers by
ordering the output alphabetically, and changing the output format
slightly.
Signed-off-by: Steffan Karger
---
src/openvpn/crypto.c | 11 +++--
src/openvpn/crypto_openssl.c | 111 +-
src/openvpn/crypto_polarssl.c | 41 ++--
tests/t_lpback.sh | 2 +-
4 files changed, 134 insertions(+), 31 deletions(-)
diff --git a/src/openvpn/crypto.c b/src/openvpn/crypto.c
index 400bf11..552e333 100644
--- a/src/openvpn/crypto.c
+++ b/src/openvpn/crypto.c
@@ -492,9 +492,14 @@ init_key_ctx (struct key_ctx *ctx, struct key *key,
dmsg (D_SHOW_KEYS, "%s: CIPHER KEY: %s", prefix,
format_hex (key->cipher, kt->cipher_length, 0, &gc));
dmsg (D_CRYPTO_DEBUG, "%s: CIPHER block_size=%d iv_size=%d",
- prefix,
- cipher_kt_block_size(kt->cipher),
- cipher_kt_iv_size(kt->cipher));
+ prefix, cipher_kt_block_size(kt->cipher),
+ cipher_kt_iv_size(kt->cipher));
+ if (cipher_kt_block_size(kt->cipher) < 128/8)
+ {
+ msg (M_WARN, "WARNING: this cipher's block size is less than 128 bit "
+ "(%d bit). Consider using a --cipher with a larger block size.",
+ cipher_kt_block_size(kt->cipher)*8);
+ }
}
if (kt->digest && kt->hmac_length > 0)
{
diff --git a/src/openvpn/crypto_openssl.c b/src/openvpn/crypto_openssl.c
index c147245..c26143a 100644
--- a/src/openvpn/crypto_openssl.c
+++ b/src/openvpn/crypto_openssl.c
@@ -288,11 +288,42 @@ translate_cipher_name_to_openvpn (const char
*cipher_name) {
return cipher_name;
}
+static int
+cipher_name_cmp(const void *a, const void *b)
+{
+ const EVP_CIPHER * const *cipher_a = a;
+ const EVP_CIPHER * const *cipher_b = b;
+
+ const char *cipher_name_a =
+ translate_cipher_name_to_openvpn(EVP_CIPHER_name(*cipher_a));
+ const char *cipher_name_b =
+ translate_cipher_name_to_openvpn(EVP_CIPHER_name(*cipher_b));
+
+ return strcmp(cipher_name_a, cipher_name_b);
+}
+
+static void
+print_cipher(const EVP_CIPHER *cipher)
+{
+ const char *var_key_size =
+ (EVP_CIPHER_flags (cipher) & EVP_CIPH_VARIABLE_LENGTH) ?
+" by default" : "";
+ const char *ssl_only = cipher_kt_mode_cbc(cipher) ?
+ "" : ", TLS client/server mode only";
+
+ printf ("%s (%d bit key%s, %d bit block%s)\n",
+ translate_cipher_name_to_openvpn (EVP_CIPHER_name (cipher)),
+ EVP_CIPHER_key_length (cipher) * 8, var_key_size,
+ cipher_kt_block_size (cipher) * 8, ssl_only);
+}
+
void
show_available_ciphers ()
{
- int nid;
-
+ /* If we ever exceed this, we must be more selective */
+ const size_t cipher_list_len = 1000;
+ const EVP_CIPHER *cipher_list[cipher_list_len];
+ size_t num_ciphers = 0;
#ifndef ENABLE_SMALL
printf ("The following ciphers and cipher modes are available\n"
"for use with " PACKAGE_NAME ". Each cipher shown below may be\n"
@@ -302,29 +333,37 @@ show_available_ciphers ()
"is recommended. In static key mode only CBC mode is allowed.\n\n");
#endif
- for (nid = 0; nid < 1; ++nid)/* is there a better way to get the
size of the nid list? */
+ for (int nid = 0; nid < 1; ++nid)
{
- const EVP_CIPHER *cipher = EVP_get_cipherbynid (nid);
- if (cipher)
- {
- if (cipher_kt_mode_cbc(cipher)
+ const EVP_CIPHER *cipher = EVP_get_cipherbynid(nid);
+ if (cipher && (cipher_kt_mode_cbc(cipher)
#ifdef ENABLE_OFB_CFB_MODE
|| cipher_kt_mode_ofb_cfb(cipher)
#endif
- )
- {
- const char *var_key_size =
- (EVP_CIPHER_flags (cipher) & EVP_CIPH_VARIABLE_LENGTH) ?
- "variable" : "fixed";
- const char *ssl_only = cipher_kt_mode_ofb_cfb(cipher) ?
- " (TLS client/server mode)" : "";
-
- printf ("%s %d bit default key (%s)%s\n", OBJ_nid2sn (nid),
- EVP_CIPHER_key_length (cipher) * 8, var_key_size,
- ssl_only);
- }
+ ))
+ {
+ cipher_list[num_ciphers++] = cipher;
+ }
+ if (num_ciphers == cipher_list_len)
+ {
+ msg (M_WARN, "WARNING: Too many ciphers, not showing all");
+ break;
}
}
+
+ qsort (cipher_list, num_ciphers, sizeof(*cipher_list), cipher_name_cmp);
+
+ for (size_t i = 0; i < num_ciphers; i++) {
+ if (cipher_kt_block_size(cipher_list[i]) >= 128/8)
+ print_cipher(cipher_list[i])
