Implement standalone FromChat Protocol

frontend/packages/fromchat-protocol/src/protocol/FromChatProtocol.ts

@@ -0,0 +1,102 @@
+import { ecdhSharedSecret, deriveWrappingKey } from "../crypto/asymmetric";
+import { importAesGcmKey, aesGcmEncrypt, aesGcmDecrypt } from "../crypto/symmetric";
+import { randomBytes } from "../crypto/kdf";
+import type { EncryptedMessage } from "./types";
+
+/**
+ * FromChat Protocol - Simple ECDH-based encryption
+ * 
+ * Protocol:
+ * 1. Generate random message key (mk) - 32 bytes
+ * 2. Generate random salt (wkSalt) - 16 bytes
+ * 3. Derive shared secret from ECDH (X25519)
+ * 4. Derive wrapping key from shared secret using HKDF with salt
+ * 5. Encrypt message with mk using AES-GCM
+ * 6. Encrypt (wrap) mk with wrapping key using AES-GCM
+ * 7. Send: { iv, ciphertext, salt, iv2, wrappedMk }
+ */
+export class FromChatProtocol {
+	private privateKey: Uint8Array;
+
+	constructor(privateKey: Uint8Array) {
+		this.privateKey = privateKey;
+	}
+
+	/**
+	 * Encrypt a message for a recipient
+	 * @param recipientPublicKey - Recipient's X25519 public key
+	 * @param plaintext - Message to encrypt
+	 * @returns Encrypted message with all necessary fields
+	 */
+	async encryptMessage(recipientPublicKey: Uint8Array, plaintext: string): Promise<EncryptedMessage> {
+		// Generate random message key
+		const mk = randomBytes(32);
+		
+		// Generate random salt for wrapping key derivation
+		const wkSalt = randomBytes(16);
+		
+		// Derive shared secret from ECDH
+		const shared = ecdhSharedSecret(this.privateKey, recipientPublicKey);
+		
+		// Derive wrapping key from shared secret using HKDF
+		const wkRaw = await deriveWrappingKey(shared, wkSalt, new Uint8Array([1]));
+		const wk = await importAesGcmKey(wkRaw);
+		
+		// Encrypt the message with message key
+		const plaintextBytes = new TextEncoder().encode(plaintext);
+		const encMsg = await aesGcmEncrypt(await importAesGcmKey(mk), plaintextBytes);
+		
+		// Encrypt (wrap) the message key with wrapping key
+		const wrap = await aesGcmEncrypt(wk, mk);
+		
+		// Convert to base64 for transmission
+		return {
+			iv: btoa(String.fromCharCode(...encMsg.iv)),
+			ciphertext: btoa(String.fromCharCode(...encMsg.ciphertext)),
+			salt: btoa(String.fromCharCode(...wkSalt)),
+			iv2: btoa(String.fromCharCode(...wrap.iv)),
+			wrappedMk: btoa(String.fromCharCode(...wrap.ciphertext))
+		};
+	}
+
+	/**
+	 * Decrypt a message from a sender
+	 * @param senderPublicKey - Sender's X25519 public key
+	 * @param message - Encrypted message
+	 * @returns Decrypted plaintext
+	 */
+	async decryptMessage(senderPublicKey: Uint8Array, message: EncryptedMessage): Promise<string> {
+		// Decode base64 fields
+		const salt = new Uint8Array(
+			atob(message.salt).split("").map(c => c.charCodeAt(0))
+		);
+		const iv2 = new Uint8Array(
+			atob(message.iv2).split("").map(c => c.charCodeAt(0))
+		);
+		const wrappedMk = new Uint8Array(
+			atob(message.wrappedMk).split("").map(c => c.charCodeAt(0))
+		);
+		const iv = new Uint8Array(
+			atob(message.iv).split("").map(c => c.charCodeAt(0))
+		);
+		const ciphertext = new Uint8Array(
+			atob(message.ciphertext).split("").map(c => c.charCodeAt(0))
+		);
+		
+		// Derive shared secret from ECDH
+		const shared = ecdhSharedSecret(this.privateKey, senderPublicKey);
+		
+		// Derive wrapping key from shared secret using salt from message
+		const wkRaw = await deriveWrappingKey(shared, salt, new Uint8Array([1]));
+		const wk = await importAesGcmKey(wkRaw);
+		
+		// Decrypt (unwrap) the message key
+		const mk = await aesGcmDecrypt(wk, iv2, wrappedMk);
+		
+		// Decrypt the message with message key
+		const decrypted = await aesGcmDecrypt(await importAesGcmKey(mk), iv, ciphertext);
+		
+		return new TextDecoder().decode(decrypted);
+	}
+}
+