diff --git a/src/ecdh.rs b/src/ecdh.rs index 4b08dbb..ca23ede 100644 --- a/src/ecdh.rs +++ b/src/ecdh.rs @@ -17,10 +17,11 @@ //! use core::ptr; -use core::ops::Deref; +use core::ops::{FnMut, Deref}; use key::{SecretKey, PublicKey}; use ffi::{self, CPtr}; +use secp256k1_sys::types::{c_int, c_uchar, c_void}; /// A tag used for recovering the public key from a compact signature #[derive(Copy, Clone)] @@ -68,7 +69,7 @@ impl SharedSecret { impl PartialEq for SharedSecret { fn eq(&self, other: &SharedSecret) -> bool { - &self.data[..self.len] == &other.data[..other.len] + self.as_ref() == other.as_ref() } } @@ -86,6 +87,22 @@ impl Deref for SharedSecret { } +unsafe extern "C" fn hash_callback(output: *mut c_uchar, x: *const c_uchar, y: *const c_uchar, data: *mut c_void) -> c_int + where F: FnMut([u8; 32], [u8; 32]) -> SharedSecret { + let callback: &mut F = &mut *(data as *mut F); + + let mut x_arr = [0; 32]; + let mut y_arr = [0; 32]; + ptr::copy_nonoverlapping(x, x_arr.as_mut_ptr(), 32); + ptr::copy_nonoverlapping(y, y_arr.as_mut_ptr(), 32); + + let secret = callback(x_arr, y_arr); + ptr::copy_nonoverlapping(secret.as_ptr(), output as *mut u8, secret.len()); + + secret.len() as c_int +} + + impl SharedSecret { /// Creates a new shared secret from a pubkey and secret key #[inline] @@ -105,6 +122,44 @@ impl SharedSecret { ss.set_len(32); // The default hash function is SHA256, which is 32 bytes long. ss } + + /// Creates a new shared secret from a pubkey and secret key with applied custom hash function + /// # Examples + /// ``` + /// # use secp256k1::ecdh::SharedSecret; + /// # use secp256k1::{Secp256k1, PublicKey, SecretKey}; + /// # fn sha2(_a: &[u8], _b: &[u8]) -> [u8; 32] {[0u8; 32]} + /// # let secp = Secp256k1::signing_only(); + /// # let secret_key = SecretKey::from_slice(&[3u8; 32]).unwrap(); + /// # let secret_key2 = SecretKey::from_slice(&[7u8; 32]).unwrap(); + /// # let public_key = PublicKey::from_secret_key(&secp, &secret_key2); + /// + /// let secret = SharedSecret::new_with_hash(&public_key, &secret_key, |x,y| { + /// let hash: [u8; 32] = sha2(&x,&y); + /// hash.into() + /// }); + /// + /// ``` + pub fn new_with_hash(point: &PublicKey, scalar: &SecretKey, mut hash_function: F) -> SharedSecret + where F: FnMut([u8; 32], [u8; 32]) -> SharedSecret + { + let mut ss = SharedSecret::empty(); + let hashfp: ffi::EcdhHashFn = hash_callback::; + + let res = unsafe { + ffi::secp256k1_ecdh( + ffi::secp256k1_context_no_precomp, + ss.get_data_mut_ptr(), + point.as_ptr(), + scalar.as_ptr(), + hashfp, + &mut hash_function as *mut F as *mut c_void, + ) + }; + debug_assert!(res >= 16); // 128 bit is the minimum for a secure hash function and the minimum we let users. + ss.set_len(res as usize); + ss + } } #[cfg(test)]