Add method to derive private keys outside the expected domain range

src/mina-signer/mina-signer.ts

@@ -99,6 +99,44 @@ class Client {
     return PublicKey.toBase58(publicKey);
   }
 
+  /**
+   * Derives the public key corresponding to a given private key. This function addresses compatibility with private keys generated by external tools that may produce keys outside the domain of the Pallas curve, that was previously accepted by the older [client_sdk](https://www.npmjs.com/package/@o1labs/client-sdk).
+   * The function first converts the input private key (in Base58 format) to a format that is compatible with the domain of the Pallas curve by applying a modulus operation. This step ensures backward compatibility with older keys that may not directly fit the Pallas curve's domain. Once the private key is in the correct domain, it is used to derive the corresponding public key.
+   * @param privateKeyBase58 - The private key (in Base58 format) used to derive the corresponding public key. The key is expected to be out of the domain of the Pallas curve and will be converted to fit within the domain as part of this process.
+   * @returns {Json.PublicKey} The derived public key in Base58 format, corresponding to the input private key, now within the domain of the Pallas curve.
+   * @remarks
+   * This function is labeled as "unsafe" due to the modulus operation applied to ensure backward compatibility, which might not adhere to strict security protocols expected in [mina-signer](https://www.npmjs.com/package/mina-signer). It is primarily intended for use cases requiring interoperability with keys managed by previous versions of the [client_sdk](https://www.npmjs.com/package/@o1labs/client-sdk) or other tools that may produce keys outside the Pallas curve's domain.
+   * It is an essential tool for migrating old keys for use with the current [mina-signer](https://www.npmjs.com/package/mina-signer) library, by allowing keys that would otherwise be rejected to be used effectively.
+   *
+   * @example
+   * ```ts
+   * // Assuming `oldPrivateKeyBase58` is a private key in Base58 format from an older client SDK
+   * const publicKeyBase58 = derivePublicKeyUnsafe(oldPrivateKeyBase58);
+   * console.log(publicKeyBase58); // Logs the derived public key in Base58 format
+   * ```
+   */
+  derivePublicKeyUnsafe(privateKeyBase58: Json.PrivateKey): Json.PublicKey {
+    let privateKey = PrivateKey.fromBase58(
+      PrivateKey.convertPrivateKeyToBase58WithMod(privateKeyBase58)
+    );
+    let publicKey = PrivateKey.toPublicKey(privateKey);
+    return PublicKey.toBase58(publicKey);
+  }
+
+  /**
+   * Converts a private key that is out of the domain of the Pallas curve to a private key in base58 format that is in the domain by taking the modulus of the private key.
+   * This is done to keep backwards compatibility with the previous version of the [client_sdk](https://www.npmjs.com/package/@o1labs/client-sdk), which did the same thing when converting a private key to base58.
+   * @param keyBase58 - The private key that is out of the domain of the Pallas curve
+   * @returns The private key that is in the domain of the Pallas curve
+   * @remarks
+   * This function is particularly useful when migrating old keys to be used by the current [mina-signer](https://www.npmjs.com/package/mina-signer) library,
+   * which may reject keys that do not fit the domain of the Pallas curve, by performing a modulus operation on the key, it ensures that keys
+   * from the older client_sdk can be made compatible.
+   */
+  convertPrivateKeyToBase58WithMod(keyBase58: string): string {
+    return PrivateKey.convertPrivateKeyToBase58WithMod(keyBase58);
+  }
+
   /**
    * Signs an arbitrary list of field elements in a SNARK-compatible way.
    * The resulting signature can be verified in o1js as follows:

src/mina-signer/package.json

@@ -1,7 +1,7 @@
 {
   "name": "mina-signer",
   "description": "Node API for signing transactions on various networks for Mina Protocol",
-  "version": "3.0.4",
+  "version": "3.0.5",
   "type": "module",
   "scripts": {
     "build": "tsc -p ../../tsconfig.mina-signer.json",

src/provable/curve-bigint.ts

@@ -143,4 +143,19 @@ const PrivateKey = {
   toPublicKey(key: PrivateKey) {
     return PublicKey.fromGroup(Group.scale(Group.generatorMina, key));
   },
+  convertPrivateKeyToBase58WithMod,
 };
+
+const Bigint256 = BinableBigint(256, () => {
+  // no check supplied, allows any string of 256 bits
+});
+const OutOfDomainKey = base58(
+  withVersionNumber(Bigint256, versionNumbers.scalar),
+  versionBytes.privateKey
+);
+
+function convertPrivateKeyToBase58WithMod(keyBase58: string): string {
+  let key = OutOfDomainKey.fromBase58(keyBase58);
+  key = mod(key, Fq.modulus);
+  return PrivateKey.toBase58(key);
+}