fix(eddsa-poseidon): set default private key as buffer (#298)

* fix(eddsa-poseidon): set default private key as buffer

The private key must be 1 of the following supported types: buffer, uint8array or text. Since it was
a hexadecimal string, it has been changed to buffer.

re #297

* test(eddsa-poseidon): add test to check private key type

re #297

* test(eddsa-poseidon): add test to check if priv key is expected value

re #297

packages/eddsa-poseidon/src/eddsa-poseidon.ts

@@ -11,12 +11,7 @@ import {
 } from "@zk-kit/baby-jubjub"
 import type { BigNumberish } from "@zk-kit/utils"
 import { crypto, requireBuffer } from "@zk-kit/utils"
-import {
-    bigNumberishToBigInt,
-    leBigIntToBuffer,
-    leBufferToBigInt,
-    bufferToHexadecimal
-} from "@zk-kit/utils/conversions"
+import { bigNumberishToBigInt, leBigIntToBuffer, leBufferToBigInt } from "@zk-kit/utils/conversions"
 import { requireBigNumberish } from "@zk-kit/utils/error-handlers"
 import F1Field from "@zk-kit/utils/f1-field"
 import * as scalar from "@zk-kit/utils/scalar"
@@ -274,7 +269,7 @@ export class EdDSAPoseidon {
      *
      * @param privateKey The private key used for signing and public key derivation.
      */
-    constructor(privateKey: Buffer | Uint8Array | string = bufferToHexadecimal(crypto.getRandomValues(32))) {
+    constructor(privateKey: Buffer | Uint8Array | string = crypto.getRandomValues(32)) {
         this.privateKey = privateKey
         this.secretScalar = deriveSecretScalar(privateKey)
         this.publicKey = derivePublicKey(privateKey)

packages/eddsa-poseidon/tests/index.test.ts

@@ -375,6 +375,8 @@ describe("EdDSAPoseidon", () => {
 
         const signature = eddsa.signMessage(message)
 
+        expect(typeof eddsa.privateKey).toBe("string")
+        expect(eddsa.privateKey).toBe(privateKey)
         expect(eddsa.secretScalar).toBe(deriveSecretScalar(privateKey))
         expect(eddsa.packedPublicKey).toBe(packPublicKey(eddsa.publicKey))
         expect(eddsa.verifySignature(message, signature)).toBeTruthy()
@@ -385,8 +387,8 @@ describe("EdDSAPoseidon", () => {
 
         const signature = eddsa.signMessage(message)
 
-        expect(typeof eddsa.privateKey).toBe("string")
-        expect(eddsa.privateKey).toHaveLength(64)
+        expect(typeof eddsa.privateKey).toBe("object")
+        expect(eddsa.privateKey).toHaveLength(32)
         expect(eddsa.secretScalar).toBe(deriveSecretScalar(eddsa.privateKey))
         expect(eddsa.packedPublicKey).toBe(packPublicKey(eddsa.publicKey))
         expect(eddsa.verifySignature(message, signature)).toBeTruthy()