Added optional export of private key

Cargo.toml

@@ -22,10 +22,12 @@ ethsign-crypto = { version = "0.3", path = "./ethsign-crypto" }
 
 [dev-dependencies]
 serde_json = "1.0"
+hex = "0.4"
 
 [features]
 default = ["secp256k1"]
 pure-rust = ["libsecp256k1"]
+export-private-key = []
 
 [workspace]
 members = [

README.md

@@ -2,9 +2,12 @@
 
 A library to read JSON keyfiles and sign Ethereum stuff.
 
+Library by defaults hide private key from access,
+but you can add --features export-private-key to export it.
+
 ## Usage:
 ```rust
-use ethsign::{Protected, KeyFile};
+use ethsign::{KeyFile, Protected};
 
 fn main() {
     let file = std::fs::File::open("./res/wallet.json").unwrap();
@@ -21,6 +24,13 @@ fn main() {
     let public = signature.recover(&message).unwrap();
     println!("{:?}", public);
 
+    #[cfg(feature = "export-private-key")]
+    {
+        //Do not print private key in that way in production code
+        let private = secret.private();
+        println!("Extracted private key: {}", hex::encode(private));
+    }
+
     // Verify the signature
     let res = public.verify(&signature, &message).unwrap();
     println!("{}", if res { "signature correct" } else { "invalid signature" });

examples/sign.rs

@@ -0,0 +1,28 @@
+use ethsign::{KeyFile, Protected};
+
+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);
+
+    #[cfg(feature = "export-private-key")]
+    {
+        //Do not print private key in that way in production code
+        let private = secret.private();
+        println!("Extracted private key: {}", hex::encode(private));
+    }
+
+    // Verify the signature
+    let res = public.verify(&signature, &message).unwrap();
+    println!("{}", if res { "signature correct" } else { "invalid signature" });
+}

src/key.rs

@@ -122,6 +122,17 @@ impl SecretKey {
         PublicKey::from_slice(&uncompressed[1..]).expect("The length of the key is correct; qed")
     }
 
+    /// Export stored, unencrypted, plain private key, use with caution
+    /// Do not expose this key in logs, etc. Use only if needed
+    #[cfg(feature = "export-private-key")]
+    pub fn private(&self) -> [u8; 32] {
+        use std::convert::TryInto;
+        self.secret
+            .as_ref()
+            .try_into()
+            .expect("The length of the key is correct; qed")
+    }
+
     /// Sign given 32-byte message with the key.
     pub fn sign(&self, message: &[u8]) -> Result<Signature, ec::Error> {
         let (v, data) = ec::sign(self.secret.as_ref(), message)?;
@@ -152,6 +163,15 @@ mod tests {
             pub_key.address().to_hex::<String>(),
             "005b3bcf82085eededd551f50de7892471ffb272"
         );
+        #[cfg(feature = "export-private-key")]
+        {
+            let secret_key = key.private();
+            assert_eq!(
+                secret_key.to_hex::<String>(),
+                "43cd5154df157a4ec26e3a04f9db252280e0c840b6a209026accb70dc124328c".to_string()
+            );
+        }
+
         assert_eq!(&pub_key.bytes().to_hex::<String>(), "782cc7dd72426893ae0d71477e41c41b03249a2b72e78eefcfe0baa9df604a8f979ab94cd23d872dac7bfa8d07d8b76b26efcbede7079f1c5cacd88fe9858f6e");
     }