[WIP] Port session keys from nucypher core

packages/shared/package.json

@@ -42,6 +42,8 @@
   "dependencies": {
     "@ethersproject/abi": "^5.8.0",
     "@ethersproject/providers": "^5.8.0",
+    "@noble/curves": "^1.8.1",
+    "@noble/hashes": "^1.7.1",
     "@nucypher/nucypher-contracts": "^0.23.0",
     "@nucypher/nucypher-core": "^0.14.5",
     "axios": "^1.8.4",

packages/shared/src/encryption/index.ts

@@ -0,0 +1 @@
+export * from './session-keys';

packages/shared/src/encryption/session-keys.ts

@@ -0,0 +1,97 @@
+import { x25519 } from '@noble/curves/ed25519';
+import { randomBytes } from '@noble/hashes/utils';
+
+/**
+ * Represents a static secret key for a session
+ * Port of the Rust SessionStaticSecret implementation
+ */
+export class SessionStaticSecret {
+  private readonly secretKey: Uint8Array;
+
+  constructor(secretKey: Uint8Array) {
+    this.secretKey = secretKey;
+  }
+
+  /**
+   * Perform Diffie-Hellman key exchange to derive a shared secret
+   * @param theirPublicKey The public key to derive a shared secret with
+   * @returns The derived shared secret
+   */
+  deriveSharedSecret(theirPublicKey: SessionStaticKey): SessionSharedSecret {
+    // Use the noble/curves implementation of X25519 DH
+    const sharedSecret = x25519.getSharedSecret(
+      this.secretKey,
+      theirPublicKey.asBytes(),
+    );
+    return new SessionSharedSecret(sharedSecret);
+  }
+
+  /**
+   * Create a secret key from a secure random number generator
+   * @returns A new SessionStaticSecret
+   */
+  static randomFromRng(csprng?: {
+    randomBytes: (n: number) => Uint8Array;
+  }): SessionStaticSecret {
+    // If no custom RNG is provided, use the default randomBytes
+    const secretKey = csprng ? csprng.randomBytes(32) : randomBytes(32); // X25519 uses 32-byte keys
+    return new SessionStaticSecret(secretKey);
+  }
+
+  /**
+   * Create a random secret key using the default RNG
+   * @returns A new SessionStaticSecret
+   */
+  static random(): SessionStaticSecret {
+    return SessionStaticSecret.randomFromRng();
+  }
+
+  /**
+   * Returns a public key corresponding to this secret key
+   * @returns The public key
+   */
+  publicKey(): SessionStaticKey {
+    const publicKey = x25519.getPublicKey(this.secretKey);
+    return new SessionStaticKey(publicKey);
+  }
+}
+
+/**
+ * Represents a public key for a session
+ */
+export class SessionStaticKey {
+  private readonly publicKey: Uint8Array;
+
+  constructor(publicKey: Uint8Array) {
+    this.publicKey = publicKey;
+  }
+
+  /**
+   * Returns the raw bytes of the public key
+   * @returns Uint8Array of the public key
+   */
+  asBytes(): Uint8Array {
+    // Return a copy to prevent external modification
+    return new Uint8Array(this.publicKey);
+  }
+}
+
+/**
+ * Represents a shared secret derived from a Diffie-Hellman key exchange
+ */
+export class SessionSharedSecret {
+  private readonly sharedSecret: Uint8Array;
+
+  constructor(sharedSecret: Uint8Array) {
+    this.sharedSecret = sharedSecret;
+  }
+
+  /**
+   * Returns the raw bytes of the shared secret
+   * @returns Uint8Array of the shared secret
+   */
+  asBytes(): Uint8Array {
+    // Return a copy to prevent external modification
+    return new Uint8Array(this.sharedSecret);
+  }
+}