KeyFile to SecretKey (#23)

* Add keyfile to secretkey conversion.

* Add usage example.

* Example in readme as well.

* Re-export KeyFile.

README.md

@@ -1,2 +1,29 @@
 # ethsign
+
 A library to read JSON keyfiles and sign Ethereum stuff.
+
+## Usage:
+```rust
+use ethsign::{Protected, KeyFile};
+
+fn main() {
+    let file = std::fs::File::open("./res/wallet.json").unwrap();
+    let key: KeyFile = serde_json::from_reader(file).unwrap();
+    let password: Protected = "".into();
+    let secret = key.to_secret_key(&password).unwrap();
+    let message = [1_u8; 32];
+
+    // Sign the message
+    let signature = secret.sign(&message).unwrap();
+    println!("{:?}", signature);
+
+    // Recover the signer
+    let public = signature.recover(&message).unwrap();
+    println!("{:?}", public);
+
+    // Verify the signature
+    let res = public.verify(&signature, &message).unwrap();
+    println!("{}", if res { "signature correct" } else { "invalid signature" });
+}
+```
+

src/keyfile.rs

@@ -2,7 +2,7 @@
 
 use crate::crypto::{self, Keccak256};
 use crate::error::Error;
-use crate::Protected;
+use crate::{SecretKey, Protected};
 
 use rand::{thread_rng, RngCore};
 use serde::{Deserialize, Serialize};
@@ -25,6 +25,13 @@ pub struct KeyFile {
     pub address: Option<Bytes>,
 }
 
+impl KeyFile {
+    /// Attemp to convert the `KeyFile` into `SecretKey`.
+    pub fn to_secret_key(&self, password: &Protected) -> Result<SecretKey, Error> {
+        SecretKey::from_crypto(&self.crypto, password)
+    }
+}
+
 /// Encrypted secret
 #[derive(Debug, PartialEq, Eq, Serialize, Deserialize)]
 pub struct Crypto {

src/lib.rs

@@ -1,4 +1,29 @@
 //! A simple library to read JSON keyfiles and sign Ethereum stuff.
+//!
+//! How to use it?
+//! ```rust
+//! use ethsign::{Protected, KeyFile};
+//!
+//! fn main() {
+//!     let file = std::fs::File::open("./res/wallet.json").unwrap();
+//!     let key: KeyFile = serde_json::from_reader(file).unwrap();
+//!     let password: Protected = "".into();
+//!     let secret = key.to_secret_key(&password).unwrap();
+//!     let message = [1_u8; 32];
+//!
+//!     // Sign the message
+//!     let signature = secret.sign(&message).unwrap();
+//!     println!("{:?}", signature);
+//!
+//!     // Recover the signer
+//!     let public = signature.recover(&message).unwrap();
+//!     println!("{:?}", public);
+//!
+//!     // Verify the signature
+//!     let res = public.verify(&signature, &message).unwrap();
+//!     println!("{}", if res { "signature correct" } else { "invalid signature" });
+//! }
+//! ```
 
 #![warn(missing_docs)]
 
@@ -19,4 +44,5 @@ pub mod keyfile;
 
 pub use self::error::Error;
 pub use self::key::{PublicKey, SecretKey, Signature};
+pub use self::keyfile::KeyFile;
 pub use self::protected::Protected;