feat(cli): e2e file encryption — file-crypto.ts + client + MCP tools

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/cli/src/crypto/file-crypto.ts

@@ -0,0 +1,90 @@
+/**
+ * File encryption for claudemesh E2E file sharing.
+ *
+ * Symmetric: crypto_secretbox_easy with random Kf (32-byte key).
+ * Key wrapping: crypto_box_seal to recipient's X25519 pub (converted from ed25519).
+ * Key opening: crypto_box_seal_open with own X25519 keypair.
+ */
+
+import { ensureSodium } from "./keypair";
+
+export interface EncryptedFile {
+  ciphertext: Uint8Array;  // secretbox ciphertext (includes MAC)
+  nonce: string;           // base64 24-byte nonce
+  key: Uint8Array;         // 32-byte symmetric Kf (keep in memory only)
+}
+
+/**
+ * Encrypt file bytes with a fresh random symmetric key.
+ * Returns ciphertext, nonce (base64), and the plaintext Kf.
+ */
+export async function encryptFile(plaintext: Uint8Array): Promise<EncryptedFile> {
+  const sodium = await ensureSodium();
+  const key = sodium.randombytes_buf(sodium.crypto_secretbox_KEYBYTES);
+  const nonce = sodium.randombytes_buf(sodium.crypto_secretbox_NONCEBYTES);
+  const ciphertext = sodium.crypto_secretbox_easy(plaintext, nonce, key);
+  return {
+    ciphertext,
+    nonce: sodium.to_base64(nonce, sodium.base64_variants.ORIGINAL),
+    key,
+  };
+}
+
+/**
+ * Decrypt file bytes with the symmetric key Kf.
+ * Returns null if decryption fails.
+ */
+export async function decryptFile(
+  ciphertext: Uint8Array,
+  nonceB64: string,
+  key: Uint8Array,
+): Promise<Uint8Array | null> {
+  const sodium = await ensureSodium();
+  try {
+    const nonce = sodium.from_base64(nonceB64, sodium.base64_variants.ORIGINAL);
+    return sodium.crypto_secretbox_open_easy(ciphertext, nonce, key);
+  } catch {
+    return null;
+  }
+}
+
+/**
+ * Seal Kf for a recipient using crypto_box_seal (ephemeral sender key).
+ * recipientPubkeyHex: ed25519 pubkey of recipient (64 hex chars).
+ * Returns base64 sealed box.
+ */
+export async function sealKeyForPeer(
+  kf: Uint8Array,
+  recipientPubkeyHex: string,
+): Promise<string> {
+  const sodium = await ensureSodium();
+  const recipientCurve = sodium.crypto_sign_ed25519_pk_to_curve25519(
+    sodium.from_hex(recipientPubkeyHex),
+  );
+  const sealed = sodium.crypto_box_seal(kf, recipientCurve);
+  return sodium.to_base64(sealed, sodium.base64_variants.ORIGINAL);
+}
+
+/**
+ * Open a sealed key blob using own ed25519 keypair (converted to X25519).
+ * Returns the 32-byte Kf or null if decryption fails.
+ */
+export async function openSealedKey(
+  sealedB64: string,
+  myPubkeyHex: string,
+  mySecretKeyHex: string,
+): Promise<Uint8Array | null> {
+  const sodium = await ensureSodium();
+  try {
+    const myCurvePub = sodium.crypto_sign_ed25519_pk_to_curve25519(
+      sodium.from_hex(myPubkeyHex),
+    );
+    const myCurveSec = sodium.crypto_sign_ed25519_sk_to_curve25519(
+      sodium.from_hex(mySecretKeyHex),
+    );
+    const sealed = sodium.from_base64(sealedB64, sodium.base64_variants.ORIGINAL);
+    return sodium.crypto_box_seal_open(sealed, myCurvePub, myCurveSec);
+  } catch {
+    return null;
+  }
+}