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diff --git a/packages/meshbay-common/src/meshbay_common/keyderive.py b/packages/meshbay-common/src/meshbay_common/keyderive.py
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+"""
+MeshBay — Key derivation from username + password.
+
+Allows Ed25519 + X25519 keypairs to be derived deterministically
+from credentials. Same inputs → same keys on any device.
+
+Algorithm: Argon2id (Python CLI / native clients)
+  salt   = SHA-256("meshbay:v1:" + username)
+  seed   = Argon2id(password, salt, length=64, ...)
+  sk_ed  = Ed25519PrivateKey.from_private_bytes(seed[:32])
+  sk_x25519 = X25519PrivateKey.from_private_bytes(seed[32:])
+
+Browser alternative (keyderive.js): uses PBKDF2-SHA512 because
+WebCrypto does not support Argon2. The two algorithms produce
+DIFFERENT keys from the same password — a user registered via Python
+CLI and via web browser will have different keypairs.
+
+Resolution: the web client generates RANDOM keypairs on first login
+(WebCrypto, stored encrypted in hub), and uses derive_keys_from_password
+only to encrypt/decrypt the stored keypair bundle. This avoids the
+algorithm mismatch problem entirely.
+
+See keyderive.js for the browser-side implementation.
+"""
+
+import hashlib
+from cryptography.hazmat.primitives.asymmetric.ed25519 import Ed25519PrivateKey
+from cryptography.hazmat.primitives.asymmetric.x25519 import X25519PrivateKey
+from cryptography.hazmat.primitives.kdf.argon2 import Argon2id
+
+
+# Argon2id parameters — same as keystore (see crypto.py)
+_ITERATIONS  = 3
+_MEMORY_COST = 65536   # 64 MB — increase to 262144 for production
+_LANES       = 4
+_SEED_LENGTH = 64      # 32 bytes Ed25519 + 32 bytes X25519
+
+
+def _derive_salt(username: str) -> bytes:
+    """Deterministic salt: SHA-256 of 'meshbay:v1:<username>'."""
+    return hashlib.sha256(f"meshbay:v1:{username}".encode()).digest()
+
+
+def derive_keys_from_password(
+    username: str,
+    password: str,
+) -> tuple[Ed25519PrivateKey, X25519PrivateKey]:
+    """
+    Derive Ed25519 + X25519 keypairs deterministically from username + password.
+
+    Properties:
+    - Same credentials always produce the same keypairs
+    - Different usernames produce different keys (even with same password)
+    - Password cannot be recovered from the public keys
+    - Changing the password invalidates all GEK bundles stored on the hub
+
+    Use for:
+    - CLI / native node registration (Argon2id available)
+    - Recovery of lost keypairs from credentials
+
+    Do NOT use for:
+    - Web browser registration (use random keypairs + encrypted bundle instead)
+    """
+    salt = _derive_salt(username)
+    kdf  = Argon2id(
+        salt=salt, length=_SEED_LENGTH,
+        iterations=_ITERATIONS, lanes=_LANES, memory_cost=_MEMORY_COST,
+    )
+    seed = kdf.derive(password.encode())
+    return (
+        Ed25519PrivateKey.from_private_bytes(seed[:32]),
+        X25519PrivateKey.from_private_bytes(seed[32:]),
+    )
+
+
+def encrypt_keypair_bundle(
+    sk_ed: Ed25519PrivateKey,
+    sk_x: X25519PrivateKey,
+    password: str,
+    username: str,
+) -> bytes:
+    """
+    Encrypt a keypair bundle with a password-derived key (for hub storage).
+    Used by web clients: random keypairs encrypted with password, stored on hub.
+    Returns: AES-256-GCM ciphertext (nonce prepended).
+    """
+    import os
+    from cryptography.hazmat.primitives.ciphers.aead import AESGCM
+    from meshbay_common.crypto import sk_to_raw
+    import msgpack
+
+    # Derive an AES key from the password (different info string from key derivation)
+    salt = hashlib.sha256(f"meshbay:bundle:v1:{username}".encode()).digest()
+    kdf  = Argon2id(salt=salt, length=32, iterations=_ITERATIONS,
+                    lanes=_LANES, memory_cost=_MEMORY_COST)
+    aes_key = kdf.derive(password.encode())
+
+    payload = msgpack.packb({
+        "sk_ed": sk_to_raw(sk_ed),
+        "sk_x":  sk_to_raw(sk_x),
+    }, use_bin_type=True)
+
+    nonce = os.urandom(12)
+    ct    = AESGCM(aes_key).encrypt(nonce, payload, None)
+    return nonce + ct
+
+
+def decrypt_keypair_bundle(
+    bundle: bytes,
+    password: str,
+    username: str,
+) -> tuple[Ed25519PrivateKey, X25519PrivateKey]:
+    """Decrypt a keypair bundle. Raises on wrong password."""
+    import msgpack
+    from cryptography.hazmat.primitives.ciphers.aead import AESGCM
+
+    salt = hashlib.sha256(f"meshbay:bundle:v1:{username}".encode()).digest()
+    kdf  = Argon2id(salt=salt, length=32, iterations=_ITERATIONS,
+                    lanes=_LANES, memory_cost=_MEMORY_COST)
+    aes_key = kdf.derive(password.encode())
+
+    nonce, ct = bundle[:12], bundle[12:]
+    payload   = AESGCM(aes_key).decrypt(nonce, ct, None)
+    data      = msgpack.unpackb(payload, raw=False)
+    return (
+        Ed25519PrivateKey.from_private_bytes(data["sk_ed"]),
+        X25519PrivateKey.from_private_bytes(data["sk_x"]),
+    )