Merge pull request #810 from sfackler/key-tag

Parameterize keys over what they contain

1 files changed, 120 insertions, 0 deletions

diff --git a/openssl/src/derive.rs b/openssl/src/derive.rs
new file mode 100644
index 00000000..fb7bbf14
--- /dev/null
+++ b/openssl/src/derive.rs
@@ -0,0 +1,120 @@
+//! Shared secret derivation.
+use ffi;
+use std::marker::PhantomData;
+use std::ptr;
+use foreign_types::ForeignTypeRef;
+
+use {cvt, cvt_p};
+use error::ErrorStack;
+use pkey::{HasPrivate, HasPublic, PKeyRef};
+
+/// A type used to derive a shared secret between two keys.
+pub struct Deriver<'a>(*mut ffi::EVP_PKEY_CTX, PhantomData<&'a ()>);
+
+impl<'a> Deriver<'a> {
+    /// Creates a new `Deriver` using the provided private key.
+    ///
+    /// This corresponds to [`EVP_PKEY_derive_init`].
+    ///
+    /// [`EVP_PKEY_derive_init`]: https://www.openssl.org/docs/man1.0.2/crypto/EVP_PKEY_derive_init.html
+    pub fn new<T>(key: &'a PKeyRef<T>) -> Result<Deriver<'a>, ErrorStack>
+    where
+        T: HasPrivate,
+    {
+        unsafe {
+            cvt_p(ffi::EVP_PKEY_CTX_new(key.as_ptr(), ptr::null_mut()))
+                .map(|p| Deriver(p, PhantomData))
+                .and_then(|ctx| cvt(ffi::EVP_PKEY_derive_init(ctx.0)).map(|_| ctx))
+        }
+    }
+
+    /// Sets the peer key used for secret derivation.
+    ///
+    /// This corresponds to [`EVP_PKEY_derive_set_peer`]:
+    ///
+    /// [`EVP_PKEY_derive_set_peer`]: https://www.openssl.org/docs/man1.0.2/crypto/EVP_PKEY_derive_init.html
+    pub fn set_peer<T>(&mut self, key: &'a PKeyRef<T>) -> Result<(), ErrorStack>
+    where
+        T: HasPublic,
+    {
+        unsafe { cvt(ffi::EVP_PKEY_derive_set_peer(self.0, key.as_ptr())).map(|_| ()) }
+    }
+
+    /// Returns the size of the shared secret.
+    ///
+    /// It can be used to size the buffer passed to [`Deriver::derive`].
+    ///
+    /// This corresponds to [`EVP_PKEY_derive`].
+    ///
+    /// [`Deriver::derive`]: #method.derive
+    /// [`EVP_PKEY_derive`]: https://www.openssl.org/docs/man1.0.2/crypto/EVP_PKEY_derive_init.html
+    pub fn len(&mut self) -> Result<usize, ErrorStack> {
+        unsafe {
+            let mut len = 0;
+            cvt(ffi::EVP_PKEY_derive(self.0, ptr::null_mut(), &mut len)).map(|_| len)
+        }
+    }
+
+    /// Derives a shared secret between the two keys, writing it into the buffer.
+    ///
+    /// Returns the number of bytes written.
+    ///
+    /// This corresponds to [`EVP_PKEY_derive`].
+    ///
+    /// [`EVP_PKEY_derive`]: https://www.openssl.org/docs/man1.0.2/crypto/EVP_PKEY_derive_init.html
+    pub fn derive(&mut self, buf: &mut [u8]) -> Result<usize, ErrorStack> {
+        let mut len = buf.len();
+        unsafe {
+            cvt(ffi::EVP_PKEY_derive(
+                self.0,
+                buf.as_mut_ptr() as *mut _,
+                &mut len,
+            )).map(|_| len)
+        }
+    }
+
+    /// A convenience function which derives a shared secret and returns it in a new buffer.
+    ///
+    /// This simply wraps [`Deriver::len`] and [`Deriver::derive`].
+    ///
+    /// [`Deriver::len`]: #method.len
+    /// [`Deriver::derive`]: #method.derive
+    pub fn derive_to_vec(&mut self) -> Result<Vec<u8>, ErrorStack> {
+        let len = self.len()?;
+        let mut buf = vec![0; len];
+        let len = self.derive(&mut buf)?;
+        buf.truncate(len);
+        Ok(buf)
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    use ec::{EcGroup, EcKey};
+    use nid::Nid;
+    use pkey::PKey;
+
+    #[test]
+    fn derive_without_peer() {
+        let group = EcGroup::from_curve_name(Nid::X9_62_PRIME256V1).unwrap();
+        let ec_key = EcKey::generate(&group).unwrap();
+        let pkey = PKey::from_ec_key(ec_key).unwrap();
+        let mut deriver = Deriver::new(&pkey).unwrap();
+        deriver.derive_to_vec().unwrap_err();
+    }
+
+    #[test]
+    fn test_ec_key_derive() {
+        let group = EcGroup::from_curve_name(Nid::X9_62_PRIME256V1).unwrap();
+        let ec_key = EcKey::generate(&group).unwrap();
+        let ec_key2 = EcKey::generate(&group).unwrap();
+        let pkey = PKey::from_ec_key(ec_key).unwrap();
+        let pkey2 = PKey::from_ec_key(ec_key2).unwrap();
+        let mut deriver = Deriver::new(&pkey).unwrap();
+        deriver.set_peer(&pkey2).unwrap();
+        let shared = deriver.derive_to_vec().unwrap();
+        assert!(!shared.is_empty());
+    }
+}