Merge #24: Add signing methods for pre-determined nonces

In some cases, the public nonce used in the signature is committed and
used in the challenge. These extra methods allow signing with a private
nonce to accommodate that. There is also support for signing a pre-hashed
byte array instead of a string message

src/wasm/key_utils.rs

@@ -32,7 +32,7 @@ use crate::{
 use blake2::Digest;
 use rand::rngs::OsRng;
 use serde::{Deserialize, Serialize};
-use tari_utilities::hex::Hex;
+use tari_utilities::hex::{from_hex, Hex};
 use wasm_bindgen::prelude::*;
 
 #[derive(Serialize, Deserialize)]
@@ -87,15 +87,62 @@ pub fn sign(private_key: &str, msg: &str) -> JsValue {
             return JsValue::from_serde(&result).unwrap();
         },
     };
-    sign_with_key(&k, msg, &mut result);
+    sign_message_with_key(&k, msg, None, &mut result);
     JsValue::from_serde(&result).unwrap()
 }
 
-#[allow(non_snake_case)]
-pub(crate) fn sign_with_key(k: &RistrettoSecretKey, msg: &str, result: &mut SignResult) {
-    let (r, R) = RistrettoPublicKey::random_keypair(&mut OsRng);
+/// Generate a Schnorr signature of a challenge (that has already been hashed) using the given private
+/// key and a specified private nonce. DO NOT reuse nonces. This method is provide for cases where a
+/// public nonce has been used
+/// in the message.
+#[wasm_bindgen]
+pub fn sign_challenge_with_nonce(private_key: &str, private_nonce: &str, challenge_as_hex: &str) -> JsValue {
+    let mut result = SignResult::default();
+    let k = match RistrettoSecretKey::from_hex(private_key) {
+        Ok(k) => k,
+        _ => {
+            result.error = "Invalid private key".to_string();
+            return JsValue::from_serde(&result).unwrap();
+        },
+    };
+    let r = match RistrettoSecretKey::from_hex(private_nonce) {
+        Ok(r) => r,
+        _ => {
+            result.error = "Invalid private nonce".to_string();
+            return JsValue::from_serde(&result).unwrap();
+        },
+    };
+
+    let e = match from_hex(challenge_as_hex) {
+        Ok(e) => e,
+        _ => {
+            result.error = "Challenge was not valid HEX".to_string();
+            return JsValue::from_serde(&result).unwrap();
+        },
+    };
+    sign_with_key(&k, &e, Some(&r), &mut result);
+    JsValue::from_serde(&result).unwrap()
+}
+
+pub(crate) fn sign_message_with_key(
+    k: &RistrettoSecretKey,
+    msg: &str,
+    r: Option<&RistrettoSecretKey>,
+    result: &mut SignResult,
+)
+{
     let e = Blake256::digest(msg.as_bytes());
-    let sig = match RistrettoSchnorr::sign(k.clone(), r, e.as_slice()) {
+    sign_with_key(k, e.as_slice(), r, result)
+}
+
+#[allow(non_snake_case)]
+pub(crate) fn sign_with_key(k: &RistrettoSecretKey, e: &[u8], r: Option<&RistrettoSecretKey>, result: &mut SignResult) {
+    let (r, R) = match r {
+        Some(r) => (r.clone(), RistrettoPublicKey::from_secret_key(r)),
+        None => RistrettoPublicKey::random_keypair(&mut OsRng),
+    };
+
+    let sig = match RistrettoSchnorr::sign(k.clone(), r, e) {
         Ok(s) => s,
         Err(e) => {
             result.error = format!("Could not create signature. {}", e.to_string());

src/wasm/keyring.rs

@@ -32,7 +32,7 @@ use crate::{
     },
     wasm::{
         commitments::CommitmentResult,
-        key_utils::{sign_with_key, SignResult},
+        key_utils::{sign_message_with_key, SignResult},
     },
 };
 use rand::rngs::OsRng;
@@ -101,7 +101,35 @@ impl KeyRing {
             return JsValue::from_serde(&result).unwrap();
         }
         let k = k.unwrap();
-        sign_with_key(&k.0, msg, &mut result);
+        sign_message_with_key(&k.0, msg, None, &mut result);
+        JsValue::from_serde(&result).unwrap()
+    }
+
+    /// Sign a message using a private key and a specific nonce
+    ///
+    /// Use can use a key in the keyring to generate a digital signature. To create the signature, the caller must
+    /// provide the `id` associated with the key, the message to sign, and a `nonce_id`. *Do not* reuse nonces.
+    /// This function is provided because in some signature schemes require the public nonce to be
+    /// part of the message.
+    ///
+    /// The return type is pretty unRust-like, but is structured to more closely model a JSON object.
+    ///
+    /// `keys::check_signature` is used to verify signatures.
+    pub fn sign_with_nonce(&self, id: &str, nonce_id: &str, msg: &str) -> JsValue {
+        let mut result = SignResult::default();
+        let k = self.keys.get(id);
+        if k.is_none() {
+            result.error = format!("Private key for '{}' does not exist", id);
+            return JsValue::from_serde(&result).unwrap();
+        }
+        let k = k.unwrap();
+        let nonce = self.keys.get(nonce_id);
+        if nonce.is_none() {
+            result.error = format!("Private nonce for `{}` does not exist", nonce_id);
+            return JsValue::from_serde(&result).unwrap();
+        }
+        let nonce = nonce.unwrap();
+        sign_message_with_key(&k.0, msg, Some(&nonce.0), &mut result);
         JsValue::from_serde(&result).unwrap()
     }
 

wasm-demo.js

@@ -22,7 +22,7 @@
 //
 
 // If you get a "module not found" error, see README.md for details on how to generate the node package
-let tari_crypto = require('./pkg');
+let tari_crypto = require('./tari_js');
 let assert = require('assert');
 
 
@@ -58,6 +58,25 @@ if (sig.error) {
     }
 }
 
+// Sign with nonce
+console.log("Signing message with predetermined nonce");
+let nonce = keys.new_key("Nonce");
+sig = keys.sign_with_nonce("Alice", "Nonce","Hello Tari");
+if (sig.error) {
+    console.log(`Error getting signature ${sig.error}`);
+} else {
+    console.log('Signature:', sig);
+    console.log("Verifying signature..");
+    let pubkey = keys.public_key("Alice");
+    console.log(`Pubkey: ${pubkey}`);
+    let check = tari_crypto.check_signature(sig.public_nonce, sig.signature, pubkey, "Hello Tari");
+    if (check.result === true) {
+        console.log("Signature is valid!");
+    } else {
+        console.log(`Invalid signature: ${check.error}`);
+    }
+}
+
 // Commitments
 const v = BigInt(10200300);
 const k = keys.private_key("Bob");