Add type for passwords. (#8920)

* Add type for passwords.

* Fix test.

* Simplify `Drop` impls of `Password` and `Memzero`.

* Spaces to tabs.

* Custom `Drop` impl for `Password`.

ethkey/src/lib.rs

@@ -27,18 +27,22 @@ extern crate quick_error;
 extern crate rand;
 extern crate rustc_hex;
 extern crate secp256k1;
+extern crate serde;
 extern crate tiny_keccak;
 
 #[macro_use]
 extern crate lazy_static;
 #[macro_use]
 extern crate log;
+#[macro_use]
+extern crate serde_derive;
 
 mod brain;
 mod brain_prefix;
 mod error;
 mod keypair;
 mod keccak;
+mod password;
 mod prefix;
 mod random;
 mod signature;
@@ -55,6 +59,7 @@ pub use self::brain_prefix::BrainPrefix;
 pub use self::error::Error;
 pub use self::keypair::{KeyPair, public_to_address};
 pub use self::math::public_is_valid;
+pub use self::password::Password;
 pub use self::prefix::Prefix;
 pub use self::random::Random;
 pub use self::signature::{sign, verify_public, verify_address, recover, Signature};

ethkey/src/password.rs

@@ -0,0 +1,60 @@
+// Copyright 2018 Parity Technologies (UK) Ltd.
+// This file is part of Parity.
+
+// Parity is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Parity is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Parity.  If not, see <http://www.gnu.org/licenses/>.
+
+use std::{fmt, ptr};
+
+#[derive(Clone, PartialEq, Eq, Serialize, Deserialize)]
+pub struct Password(String);
+
+impl fmt::Debug for Password {
+	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "Password(******)")
+    }
+}
+
+impl Password {
+	pub fn as_bytes(&self) -> &[u8] {
+		self.0.as_bytes()
+	}
+
+	pub fn as_str(&self) -> &str {
+		self.0.as_str()
+	}
+}
+
+// Custom drop impl to zero out memory.
+impl Drop for Password {
+	fn drop(&mut self) {
+		unsafe {
+			for byte_ref in self.0.as_mut_vec() {
+				ptr::write_volatile(byte_ref, 0)
+			}
+		}
+	}
+}
+
+impl From<String> for Password {
+	fn from(s: String) -> Password {
+		Password(s)
+	}
+}
+
+impl<'a> From<&'a str> for Password {
+	fn from(s: &'a str) -> Password {
+		Password::from(String::from(s))
+	}
+}
+