From 72f181539118828ca966a0f8d03f6428e2bcf0d6 Mon Sep 17 00:00:00 2001 From: "Dr. Stephen Henson" Date: Thu, 23 Oct 2014 17:09:57 +0100 Subject: [PATCH 06/15] Only allow ephemeral RSA keys in export ciphersuites. OpenSSL clients would tolerate temporary RSA keys in non-export ciphersuites. It also had an option SSL_OP_EPHEMERAL_RSA which enabled this server side. Remove both options as they are a protocol violation. Thanks to Karthikeyan Bhargavan for reporting this issue. (CVE-2015-0204) Reviewed-by: Matt Caswell Reviewed-by: Tim Hudson (cherry picked from commit 4b4c1fcc88aec8c9e001b0a0077d3cd4de1ed0e6) Conflicts: doc/ssl/SSL_CTX_set_options.pod ssl/d1_srvr.c ssl/s3_srvr.c --- doc/ssl/SSL_CTX_set_options.pod | 10 +--------- doc/ssl/SSL_CTX_set_tmp_rsa_callback.pod | 23 ++++++++--------------- ssl/d1_srvr.c | 16 ++-------------- ssl/s3_clnt.c | 7 +++++++ ssl/s3_srvr.c | 16 ++-------------- ssl/ssl.h | 5 ++--- 7 files changed, 30 insertions(+), 55 deletions(-) diff --git a/doc/ssl/SSL_CTX_set_options.pod b/doc/ssl/SSL_CTX_set_options.pod index a2a570b..307b157 100644 --- a/doc/ssl/SSL_CTX_set_options.pod +++ b/doc/ssl/SSL_CTX_set_options.pod @@ -152,15 +152,7 @@ temporary/ephemeral DH parameters are used. =item SSL_OP_EPHEMERAL_RSA -Always use ephemeral (temporary) RSA key when doing RSA operations -(see L). -According to the specifications this is only done, when a RSA key -can only be used for signature operations (namely under export ciphers -with restricted RSA keylength). By setting this option, ephemeral -RSA keys are always used. This option breaks compatibility with the -SSL/TLS specifications and may lead to interoperability problems with -clients and should therefore never be used. Ciphers with EDH (ephemeral -Diffie-Hellman) key exchange should be used instead. +This option is no longer implemented and is treated as no op. =item SSL_OP_CIPHER_SERVER_PREFERENCE diff --git a/doc/ssl/SSL_CTX_set_tmp_rsa_callback.pod b/doc/ssl/SSL_CTX_set_tmp_rsa_callback.pod index 534643c..8794eb7 100644 --- a/doc/ssl/SSL_CTX_set_tmp_rsa_callback.pod +++ b/doc/ssl/SSL_CTX_set_tmp_rsa_callback.pod @@ -74,21 +74,14 @@ exchange and use EDH (Ephemeral Diffie-Hellman) key exchange instead in order to achieve forward secrecy (see L). -On OpenSSL servers ephemeral RSA key exchange is therefore disabled by default -and must be explicitly enabled using the SSL_OP_EPHEMERAL_RSA option of -L, violating the TLS/SSL -standard. When ephemeral RSA key exchange is required for export ciphers, -it will automatically be used without this option! - -An application may either directly specify the key or can supply the key via -a callback function. The callback approach has the advantage, that the -callback may generate the key only in case it is actually needed. As the -generation of a RSA key is however costly, it will lead to a significant -delay in the handshake procedure. Another advantage of the callback function -is that it can supply keys of different size (e.g. for SSL_OP_EPHEMERAL_RSA -usage) while the explicit setting of the key is only useful for key size of -512 bits to satisfy the export restricted ciphers and does give away key length -if a longer key would be allowed. +An application may either directly specify the key or can supply the key via a +callback function. The callback approach has the advantage, that the callback +may generate the key only in case it is actually needed. As the generation of a +RSA key is however costly, it will lead to a significant delay in the handshake +procedure. Another advantage of the callback function is that it can supply +keys of different size while the explicit setting of the key is only useful for +key size of 512 bits to satisfy the export restricted ciphers and does give +away key length if a longer key would be allowed. The B is called with the B needed and the B information. The B flag is set, when the diff --git a/ssl/d1_srvr.c b/ssl/d1_srvr.c index 0e6bf46..0e9bb20 100644 --- a/ssl/d1_srvr.c +++ b/ssl/d1_srvr.c @@ -371,23 +371,11 @@ int dtls1_accept(SSL *s) /* clear this, it may get reset by * send_server_key_exchange */ - if ((s->options & SSL_OP_EPHEMERAL_RSA) -#ifndef OPENSSL_NO_KRB5 - && !(l & SSL_KRB5) -#endif /* OPENSSL_NO_KRB5 */ - ) - /* option SSL_OP_EPHEMERAL_RSA sends temporary RSA key - * even when forbidden by protocol specs - * (handshake may fail as clients are not required to - * be able to handle this) */ - s->s3->tmp.use_rsa_tmp=1; - else - s->s3->tmp.use_rsa_tmp=0; + s->s3->tmp.use_rsa_tmp=0; /* only send if a DH key exchange, fortezza or * RSA but we have a sign only certificate */ - if (s->s3->tmp.use_rsa_tmp - || (l & (SSL_DH|SSL_kFZA)) + if ((l & (SSL_DH|SSL_kFZA)) || ((l & SSL_kRSA) && (s->cert->pkeys[SSL_PKEY_RSA_ENC].privatekey == NULL || (SSL_C_IS_EXPORT(s->s3->tmp.new_cipher) diff --git a/ssl/s3_clnt.c b/ssl/s3_clnt.c index 256fc94..2402a06 100644 --- a/ssl/s3_clnt.c +++ b/ssl/s3_clnt.c @@ -1180,6 +1180,13 @@ int ssl3_get_key_exchange(SSL *s) #ifndef OPENSSL_NO_RSA if (alg & SSL_kRSA) { + /* Temporary RSA keys only allowed in export ciphersuites */ + if (!SSL_C_IS_EXPORT(s->s3->tmp.new_cipher)) + { + al=SSL_AD_UNEXPECTED_MESSAGE; + SSLerr(SSL_F_SSL3_GET_SERVER_CERTIFICATE,SSL_R_UNEXPECTED_MESSAGE); + goto f_err; + } if ((rsa=RSA_new()) == NULL) { SSLerr(SSL_F_SSL3_GET_KEY_EXCHANGE,ERR_R_MALLOC_FAILURE); diff --git a/ssl/s3_srvr.c b/ssl/s3_srvr.c index ca3e77a..18832e9 100644 --- a/ssl/s3_srvr.c +++ b/ssl/s3_srvr.c @@ -355,18 +355,7 @@ int ssl3_accept(SSL *s) /* clear this, it may get reset by * send_server_key_exchange */ - if ((s->options & SSL_OP_EPHEMERAL_RSA) -#ifndef OPENSSL_NO_KRB5 - && !(l & SSL_KRB5) -#endif /* OPENSSL_NO_KRB5 */ - ) - /* option SSL_OP_EPHEMERAL_RSA sends temporary RSA key - * even when forbidden by protocol specs - * (handshake may fail as clients are not required to - * be able to handle this) */ - s->s3->tmp.use_rsa_tmp=1; - else - s->s3->tmp.use_rsa_tmp=0; + s->s3->tmp.use_rsa_tmp=0; /* only send if a DH key exchange, fortezza or @@ -378,8 +367,7 @@ int ssl3_accept(SSL *s) * server certificate contains the server's * public key for key exchange. */ - if (s->s3->tmp.use_rsa_tmp - || (l & SSL_kECDHE) + if ((l & SSL_kECDHE) || (l & (SSL_DH|SSL_kFZA)) || ((l & SSL_kRSA) && (s->cert->pkeys[SSL_PKEY_RSA_ENC].privatekey == NULL diff --git a/ssl/ssl.h b/ssl/ssl.h index 4ea0d80..8420100 100644 --- a/ssl/ssl.h +++ b/ssl/ssl.h @@ -526,9 +526,8 @@ typedef struct ssl_session_st #define SSL_OP_SINGLE_ECDH_USE 0x00080000L /* If set, always create a new key when using tmp_dh parameters */ #define SSL_OP_SINGLE_DH_USE 0x00100000L -/* Set to always use the tmp_rsa key when doing RSA operations, - * even when this violates protocol specs */ -#define SSL_OP_EPHEMERAL_RSA 0x00200000L +/* Does nothing: retained for compatibiity */ +#define SSL_OP_EPHEMERAL_RSA 0x0 /* Set on servers to choose the cipher according to the server's * preferences */ #define SSL_OP_CIPHER_SERVER_PREFERENCE 0x00400000L -- 2.1.4