Add support for set_tmp_dh() and RFC5114 DH parameters for forward secrecy.

rust-openssl didn't support forward secrecy at all.

This adds support for DHE, by exposing set_tmp_dh() as well as the RFC5114
parameters, which are conveniently exposed since OpenSSL 1.0.2.

With OpenSSL >= 1.0.2, and the rfc5114 feature gate, enabling DHE is as simple
as (here for 2048-bit MODP group with 256-bit prime order subgroup):

    use openssl::dh::DH;
    let dh = DH::get_2048_256().unwrap();
    ctx.set_tmp_dh(dh).unwrap();

With OpenSSL < 1.0.2, DH::from_params() can be used to manually specify the
DH parameters (here for 2048-bit MODP group with 256-bit prime order subgroup):

    use openssl::bn::BigNum;
    use openssl::dh::DH;
    let p = BigNum::from_hex_str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unwrap();
    let g = BigNum::from_hex_str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unwrap();
    let q = BigNum::from_hex_str("8CF83642A709A097B447997640129DA299B1A47D1EB3750BA308B0FE64F5FBD3").unwrap();
    let dh = DH::from_params(p, g, q).unwrap();
    ctx.set_tmp_dh(dh).unwrap();

2 files changed, 32 insertions, 0 deletions

diff --git a/openssl-sys/src/lib.rs b/openssl-sys/src/lib.rs
index b3025be1..c2dafb5d 100644
--- a/openssl-sys/src/lib.rs
+++ b/openssl-sys/src/lib.rs
@@ -20,6 +20,7 @@ pub type BIO_METHOD = c_void;
 pub type BN_CTX = c_void;
 pub type COMP_METHOD = c_void;
 pub type CRYPTO_EX_DATA = c_void;
+pub type DH = c_void;
 pub type ENGINE = c_void;
 pub type EVP_CIPHER = c_void;
 pub type EVP_CIPHER_CTX = c_void;
@@ -380,6 +381,17 @@ extern "C" {
     pub fn CRYPTO_memcmp(a: *const c_void, b: *const c_void,
                          len: size_t) -> c_int;
 
+    pub fn DH_free(dh: *mut DH);
+
+    #[cfg(feature = "rfc5114")]
+    pub fn DH_get_1024_160() -> *mut DH;
+    #[cfg(feature = "rfc5114")]
+    pub fn DH_get_2048_224() -> *mut DH;
+    #[cfg(feature = "rfc5114")]
+    pub fn DH_get_2048_256() -> *mut DH;
+
+    pub fn DH_new_from_params(p: *mut BIGNUM, g: *mut BIGNUM, q: *mut BIGNUM) -> *mut DH;
+
     pub fn ERR_get_error() -> c_ulong;
 
     pub fn ERR_lib_error_string(err: c_ulong) -> *const c_char;
@@ -664,6 +676,8 @@ extern "C" {
     pub fn SSL_CTX_set_read_ahead(ctx: *mut SSL_CTX, m: c_long) -> c_long;
     #[link_name = "SSL_set_tlsext_host_name_shim"]
     pub fn SSL_set_tlsext_host_name(s: *mut SSL, name: *const c_char) -> c_long;
+    #[link_name = "SSL_CTX_set_tmp_dh_shim"]
+    pub fn SSL_CTX_set_tmp_dh(s: *mut SSL, dh: *const DH) -> c_long;
     #[link_name = "X509_get_extensions_shim"]
     pub fn X509_get_extensions(x: *mut X509) -> *mut stack_st_X509_EXTENSION;
 }
diff --git a/openssl-sys/src/openssl_shim.c b/openssl-sys/src/openssl_shim.c
index f0622d2d..ce0ee692 100644
--- a/openssl-sys/src/openssl_shim.c
+++ b/openssl-sys/src/openssl_shim.c
@@ -1,5 +1,7 @@
 #include <openssl/hmac.h>
 #include <openssl/ssl.h>
+#include <openssl/dh.h>
+#include <openssl/bn.h>
 
 #if OPENSSL_VERSION_NUMBER < 0x1000000L
 // Copied from openssl crypto/hmac/hmac.c
@@ -79,6 +81,22 @@ long SSL_CTX_set_read_ahead_shim(SSL_CTX *ctx, long m) {
     return SSL_CTX_set_read_ahead(ctx, m);
 }
 
+long SSL_CTX_set_tmp_dh_shim(SSL_CTX *ctx, DH *dh) {
+    return SSL_CTX_set_tmp_dh(ctx, dh);
+}
+
+DH *DH_new_from_params(BIGNUM *p, BIGNUM *g, BIGNUM *q) {
+    DH *dh;
+
+    if ((dh = DH_new()) == NULL) {
+        return NULL;
+    }
+    dh->p = p;
+    dh->g = g;
+    dh->q = q;
+    return dh;
+}
+
 long SSL_set_tlsext_host_name_shim(SSL *s, char *name) {
     return SSL_set_tlsext_host_name(s, name);
 }