Disable old and unsecure ciphers in TLS driver

Disable:
- export ciphers - broken by design, 40 and 56 bit encryption
- low encryption ciphers - 56 and 64 bit encryption
- SSLv2 ciphers - some ciphers using MD5 MAC

src/tls/tls_drv.c

@@ -44,6 +44,8 @@ typedef unsigned __int32 uint32_t;
 #define SSL_OP_NO_TICKET 0
 #endif
 
+#define CIPHERS "DEFAULT:!EXPORT:!LOW:!SSLv2"
+
 /*
  * R15B changed several driver callbacks to use ErlDrvSizeT and
  * ErlDrvSSizeT typedefs instead of int.
@@ -354,6 +356,8 @@ static ErlDrvSSizeT tls_drv_control(ErlDrvData handle,
 	    res = SSL_CTX_check_private_key(ctx);
 	    die_unless(res > 0, "SSL_CTX_check_private_key failed");
 
+	    SSL_CTX_set_cipher_list(ctx, CIPHERS);
+
 	    SSL_CTX_set_session_cache_mode(ctx, SSL_SESS_CACHE_OFF);
 	    SSL_CTX_set_default_verify_paths(ctx);
 #ifdef SSL_MODE_RELEASE_BUFFERS