From 892d66e422d5367673163d62ba40cd70a37d5cf7 Mon Sep 17 00:00:00 2001 From: Christian Heimes Date: Mon, 29 Jan 2018 14:10:18 +0100 Subject: bpo-31429: Define TLS cipher suite on build time (#3532) Until now Python used a hard coded white list of default TLS cipher suites. The old approach has multiple downsides. OpenSSL's default selection was completely overruled. Python did neither benefit from new cipher suites (ChaCha20, TLS 1.3 suites) nor blacklisted cipher suites. For example we used to re-enable 3DES. Python now defaults to OpenSSL DEFAULT cipher suite selection and black lists all unwanted ciphers. Downstream vendors can override the default cipher list with --with-ssl-default-suites. Signed-off-by: Christian Heimes --- Modules/_ssl.c | 35 ++++++++++++++++++++++++++++++++++- 1 file changed, 34 insertions(+), 1 deletion(-) (limited to 'Modules/_ssl.c') diff --git a/Modules/_ssl.c b/Modules/_ssl.c index ec8c8af54b..7545e91bab 100644 --- a/Modules/_ssl.c +++ b/Modules/_ssl.c @@ -234,6 +234,31 @@ SSL_SESSION_get_ticket_lifetime_hint(const SSL_SESSION *s) #endif /* OpenSSL < 1.1.0 or LibreSSL */ +/* Default cipher suites */ +#ifndef PY_SSL_DEFAULT_CIPHERS +#define PY_SSL_DEFAULT_CIPHERS 1 +#endif + +#if PY_SSL_DEFAULT_CIPHERS == 0 + #ifndef PY_SSL_DEFAULT_CIPHER_STRING + #error "Py_SSL_DEFAULT_CIPHERS 0 needs Py_SSL_DEFAULT_CIPHER_STRING" + #endif +#elif PY_SSL_DEFAULT_CIPHERS == 1 +/* Python custom selection of sensible ciper suites + * DEFAULT: OpenSSL's default cipher list. Since 1.0.2 the list is in sensible order. + * !aNULL:!eNULL: really no NULL ciphers + * !MD5:!3DES:!DES:!RC4:!IDEA:!SEED: no weak or broken algorithms on old OpenSSL versions. + * !aDSS: no authentication with discrete logarithm DSA algorithm + * !SRP:!PSK: no secure remote password or pre-shared key authentication + */ + #define PY_SSL_DEFAULT_CIPHER_STRING "DEFAULT:!aNULL:!eNULL:!MD5:!3DES:!DES:!RC4:!IDEA:!SEED:!aDSS:!SRP:!PSK" +#elif PY_SSL_DEFAULT_CIPHERS == 2 +/* Ignored in SSLContext constructor, only used to as _ssl.DEFAULT_CIPHER_STRING */ + #define PY_SSL_DEFAULT_CIPHER_STRING SSL_DEFAULT_CIPHER_LIST +#else + #error "Unsupported PY_SSL_DEFAULT_CIPHERS" +#endif + enum py_ssl_error { /* these mirror ssl.h */ @@ -2873,7 +2898,12 @@ _ssl__SSLContext_impl(PyTypeObject *type, int proto_version) /* A bare minimum cipher list without completely broken cipher suites. * It's far from perfect but gives users a better head start. */ if (proto_version != PY_SSL_VERSION_SSL2) { - result = SSL_CTX_set_cipher_list(ctx, "HIGH:!aNULL:!eNULL:!MD5"); +#if PY_SSL_DEFAULT_CIPHERS == 2 + /* stick to OpenSSL's default settings */ + result = 1; +#else + result = SSL_CTX_set_cipher_list(ctx, PY_SSL_DEFAULT_CIPHER_STRING); +#endif } else { /* SSLv2 needs MD5 */ result = SSL_CTX_set_cipher_list(ctx, "HIGH:!aNULL:!eNULL"); @@ -5430,6 +5460,9 @@ PyInit__ssl(void) (PyObject *)&PySSLSession_Type) != 0) return NULL; + PyModule_AddStringConstant(m, "_DEFAULT_CIPHERS", + PY_SSL_DEFAULT_CIPHER_STRING); + PyModule_AddIntConstant(m, "SSL_ERROR_ZERO_RETURN", PY_SSL_ERROR_ZERO_RETURN); PyModule_AddIntConstant(m, "SSL_ERROR_WANT_READ", -- cgit v1.2.1