Add `Secp256k1::with_rng`, parameterize `Secp256k1` over its RNG.

Now that you can't create secret keys by directly passing a Rng to
`SecretKey::new`, we need a way to allow user-chosed randomness.
We add it to the `Secp256k1`.

src/key.rs

@@ -55,7 +55,7 @@ fn random_32_bytes<R:Rng>(rng: &mut R) -> [u8; 32] {
 impl SecretKey {
     /// Creates a new random secret key
     #[inline]
-    pub fn new(secp: &mut Secp256k1) -> SecretKey {
+    pub fn new<R: Rng>(secp: &mut Secp256k1<R>) -> SecretKey {
         let mut data = random_32_bytes(&mut secp.rng);
         unsafe {
             while ffi::secp256k1_ec_seckey_verify(secp.ctx, data.as_ptr()) == 0 {
@@ -67,7 +67,8 @@ impl SecretKey {
 
     /// Converts a `SECRET_KEY_SIZE`-byte slice to a secret key
     #[inline]
-    pub fn from_slice(secp: &Secp256k1, data: &[u8]) -> Result<SecretKey, Error> {
+    pub fn from_slice<R: Rng>(secp: &Secp256k1<R>, data: &[u8])
+                             -> Result<SecretKey, Error> {
         match data.len() {
             constants::SECRET_KEY_SIZE => {
                 let mut ret = [0; constants::SECRET_KEY_SIZE];
@@ -87,7 +88,10 @@ impl SecretKey {
 
     #[inline]
     /// Adds one secret key to another, modulo the curve order
-    pub fn add_assign(&mut self, secp: &Secp256k1, other: &SecretKey) -> Result<(), Error> {
+    pub fn add_assign<R: Rng>(&mut self,
+                              secp: &Secp256k1<R>,
+                              other: &SecretKey)
+                             -> Result<(), Error> {
         unsafe {
             if ffi::secp256k1_ec_privkey_tweak_add(secp.ctx, self.as_mut_ptr(), other.as_ptr()) != 1 {
                 Err(Unknown)
@@ -113,7 +117,10 @@ impl PublicKey {
 
     /// Creates a new public key from a secret key.
     #[inline]
-    pub fn from_secret_key(secp: &Secp256k1, sk: &SecretKey, compressed: bool) -> PublicKey {
+    pub fn from_secret_key<R: Rng>(secp: &Secp256k1<R>,
+                                   sk: &SecretKey,
+                                   compressed: bool)
+                                  -> PublicKey {
         let mut pk = PublicKey::new(compressed);
         let compressed = if compressed {1} else {0};
         let mut len = 0;
@@ -132,7 +139,8 @@ impl PublicKey {
 
     /// Creates a public key directly from a slice
     #[inline]
-    pub fn from_slice(secp: &Secp256k1, data: &[u8]) -> Result<PublicKey, Error> {
+    pub fn from_slice<R: Rng>(secp: &Secp256k1<R>, data: &[u8])
+                             -> Result<PublicKey, Error> {
         match data.len() {
             constants::COMPRESSED_PUBLIC_KEY_SIZE => {
                 let mut ret = [0; constants::COMPRESSED_PUBLIC_KEY_SIZE];
@@ -204,7 +212,10 @@ impl PublicKey {
 
     #[inline]
     /// Adds the pk corresponding to `other` to the pk `self` in place
-    pub fn add_exp_assign(&mut self, secp: &Secp256k1, other: &SecretKey) -> Result<(), Error> {
+    pub fn add_exp_assign<R: Rng>(&mut self,
+                                  secp: &Secp256k1<R>,
+                                  other: &SecretKey)
+                                 -> Result<(), Error> {
         unsafe {
             if ffi::secp256k1_ec_pubkey_tweak_add(secp.ctx, self.as_mut_ptr(),
                                                   self.len() as ::libc::c_int,

src/lib.rs

@@ -212,28 +212,37 @@ impl fmt::Display for Error {
 }
 
 /// The secp256k1 engine, used to execute all signature operations
-pub struct Secp256k1 {
+pub struct Secp256k1<R: Rng = Fortuna> {
     ctx: ffi::Context,
-    rng: Fortuna
+    rng: R
 }
 
-impl Drop for Secp256k1 {
+impl<R: Rng> Drop for Secp256k1<R> {
     fn drop(&mut self) {
         unsafe { ffi::secp256k1_context_destroy(self.ctx); }
     }
 }
 
-impl Secp256k1 {
-    /// Constructs a new secp256k1 engine.
-    pub fn new() -> io::Result<Secp256k1> {
+impl Secp256k1<Fortuna> {
+    /// Constructs a new secp256k1 engine with the default key-generation Rng
+    /// (a Fortuna seeded with randomness from the OS during `new`)
+    pub fn new() -> io::Result<Secp256k1<Fortuna>> {
+        let mut osrng = try!(OsRng::new());
+        let mut seed = [0; 2048];
+        osrng.fill_bytes(&mut seed);
+        let rng: Fortuna = SeedableRng::from_seed(&seed[..]);
+        Secp256k1::with_rng(rng)
+    }
+}
+
+impl<R: Rng> Secp256k1<R> {
+    /// Constructs a new secp256k1 engine with its key-generation RNG specified
+    pub fn with_rng(rng: R) -> io::Result<Secp256k1<R>> {
         let ctx = unsafe {
             ffi::secp256k1_context_create(ffi::SECP256K1_START_VERIFY |
                                           ffi::SECP256K1_START_SIGN)
         };
-        let mut osrng = try!(OsRng::new());
-        let mut seed = [0; 2048];
-        osrng.fill_bytes(&mut seed);
-        Ok(Secp256k1 { ctx: ctx, rng: SeedableRng::from_seed(&seed[..]) })
+        Ok(Secp256k1 { ctx: ctx, rng: rng })
     }
 
     /// Generates a random keypair. Convenience function for `key::SecretKey::new`