On 19/10/2021 20:31, Arne Schwabe wrote:
We do not support CTS algorithms (cipher text stealing) algorithms.Signed-off-by: Arne Schwabe <a...@rfc2549.org> --- src/openvpn/crypto_openssl.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/src/openvpn/crypto_openssl.c b/src/openvpn/crypto_openssl.c index ab552efab..ac8287440 100644 --- a/src/openvpn/crypto_openssl.c +++ b/src/openvpn/crypto_openssl.c @@ -760,6 +760,9 @@ cipher_kt_mode_cbc(const cipher_kt_t *cipher) { return cipher && cipher_kt_mode(cipher) == OPENVPN_MODE_CBC /* Exclude AEAD cipher modes, they require a different API */ +#ifdef EVP_CIPH_FLAG_CTS + && !(EVP_CIPHER_flags(cipher) & EVP_CIPH_FLAG_CTS) +#endif && !(EVP_CIPHER_flags(cipher) & EVP_CIPH_FLAG_AEAD_CIPHER); }
Together with the previous patch, this makes the tests work. One thing I'm unsure about is that this check is only done for CBC mode. Cipher-text stealing can be used in *any* block cipher mode (even CTR, though that would be amazingly pointless).
I compiled OpenVPN with support for OFB and CFB modes and didn't see any CTS in the --show-ciphers output. But do we know for sure that there's no supported version or configuration of OpenSSL that uses cipher-text stealing in non-CBC modes?
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