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();

4 files changed, 107 insertions, 2 deletions

diff --git a/openssl/src/bn/mod.rs b/openssl/src/bn/mod.rs
index ccf28337..3c973438 100644
--- a/openssl/src/bn/mod.rs
+++ b/openssl/src/bn/mod.rs
@@ -397,12 +397,12 @@ impl BigNum {
         (self.num_bits() + 7) / 8
     }
 
-    unsafe fn raw(&self) -> *mut ffi::BIGNUM {
+    pub unsafe fn raw(&self) -> *mut ffi::BIGNUM {
         let BigNum(n) = *self;
         n
     }
 
-    unsafe fn raw_ptr(&self) -> *const *mut ffi::BIGNUM {
+    pub unsafe fn raw_ptr(&self) -> *const *mut ffi::BIGNUM {
         let BigNum(ref n) = *self;
         n
     }
diff --git a/openssl/src/dh/mod.rs b/openssl/src/dh/mod.rs
new file mode 100644
index 00000000..cbf9d3ab
--- /dev/null
+++ b/openssl/src/dh/mod.rs
@@ -0,0 +1,97 @@
+use ffi;
+use ssl::error::SslError;
+use bn::BigNum;
+use std::mem;
+use std::ptr;
+
+pub struct DH(*mut ffi::DH);
+
+impl DH {
+    pub fn from_params(p: BigNum, g: BigNum, q: BigNum) -> Result<DH, SslError> {
+        let dh = unsafe { ffi::DH_new_from_params(p.raw(), g.raw(), q.raw()) };
+        if dh == ptr::null_mut() {
+            return Err(SslError::get());
+        }
+        mem::forget(p);
+        mem::forget(g);
+        mem::forget(q);
+        Ok(DH(dh))
+    }
+
+    #[cfg(feature = "rfc5114")]
+    pub fn get_1024_160() -> Result<DH, SslError> {
+        let dh = unsafe { ffi::DH_get_1024_160() };
+        if dh == ptr::null_mut() {
+            return Err(SslError::get());
+        }
+        Ok(DH(dh))
+    }
+
+    #[cfg(feature = "rfc5114")]
+    pub fn get_2048_224() -> Result<DH, SslError> {
+        let dh = unsafe { ffi::DH_get_2048_224() };
+        if dh == ptr::null_mut() {
+            return Err(SslError::get());
+        }
+        Ok(DH(dh))
+    }
+
+    #[cfg(feature = "rfc5114")]
+    pub fn get_2048_256() -> Result<DH, SslError> {
+        let dh = unsafe { ffi::DH_get_2048_256() };
+        if dh == ptr::null_mut() {
+            return Err(SslError::get());
+        }
+        Ok(DH(dh))
+    }
+
+    pub unsafe fn raw(&self) -> *mut ffi::DH {
+        let DH(n) = *self;
+        n
+    }
+
+    pub unsafe fn raw_ptr(&self) -> *const *mut ffi::DH {
+        let DH(ref n) = *self;
+        n
+    }
+}
+
+impl Drop for DH {
+    fn drop(&mut self) {
+        unsafe {
+            if !self.raw().is_null() {
+                ffi::DH_free(self.raw())
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::DH;
+    use bn::BigNum;
+    use ssl::SslContext;
+    use ssl::SslMethod::Sslv23;
+
+    #[test]
+    #[cfg(feature = "rfc5114")]
+    fn test_dh_rfc5114() {
+        let ctx = SslContext::new(Sslv23).unwrap();
+        let dh1 = DH::get_1024_160().unwrap();
+        ctx.set_tmp_dh(dh1).unwrap();
+        let dh2 = DH::get_2048_224().unwrap();
+        ctx.set_tmp_dh(dh2).unwrap();
+        let dh3 = DH::get_2048_256().unwrap();
+        ctx.set_tmp_dh(dh3).unwrap();
+    }
+
+    #[test]
+    fn test_dh() {
+        let ctx = SslContext::new(Sslv23).unwrap();
+        let p = BigNum::from_hex_str("87A8E61DB4B6663CFFBBD19C651959998CEEF608660DD0F25D2CEED4435E3B00E00DF8F1D61957D4FAF7DF4561B2AA3016C3D91134096FAA3BF4296D830E9A7C209E0C6497517ABD5A8A9D306BCF67ED91F9E6725B4758C022E0B1EF4275BF7B6C5BFC11D45F9088B941F54EB1E59BB8BC39A0BF12307F5C4FDB70C581B23F76B63ACAE1CAA6B7902D52526735488A0EF13C6D9A51BFA4AB3AD8347796524D8EF6A167B5A41825D967E144E5140564251CCACB83E6B486F6B3CA3F7971506026C0B857F689962856DED4010ABD0BE621C3A3960A54E710C375F26375D7014103A4B54330C198AF126116D2276E11715F693877FAD7EF09CADB094AE91E1A1597").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();
+    }
+}
diff --git a/openssl/src/lib.rs b/openssl/src/lib.rs
index 62d18dce..f57dcdac 100644
--- a/openssl/src/lib.rs
+++ b/openssl/src/lib.rs
@@ -20,6 +20,7 @@ pub mod asn1;
 pub mod bn;
 pub mod bio;
 pub mod crypto;
+pub mod dh;
 pub mod ssl;
 pub mod x509;
 pub mod nid;
diff --git a/openssl/src/ssl/mod.rs b/openssl/src/ssl/mod.rs
index 35180d3a..ee2e1f9f 100644
--- a/openssl/src/ssl/mod.rs
+++ b/openssl/src/ssl/mod.rs
@@ -21,6 +21,7 @@ use std::slice;
 
 use bio::{MemBio};
 use ffi;
+use dh::DH;
 use ssl::error::{SslError, SslSessionClosed, StreamError, OpenSslErrors};
 use x509::{X509StoreContext, X509FileType, X509};
 use crypto::pkey::PKey;
@@ -492,6 +493,12 @@ impl SslContext {
         }
     }
 
+    pub fn set_tmp_dh(&self, dh: DH) -> Result<(),SslError> {
+        wrap_ssl_result(unsafe {
+            ffi::SSL_CTX_set_tmp_dh(self.ctx, dh.raw()) as i32
+        })
+    }
+
     #[allow(non_snake_case)]
     /// Specifies the file that contains trusted CA certificates.
     pub fn set_CA_file<P: AsRef<Path>>(&mut self, file: P) -> Result<(),SslError> {