AzelusLightvale-ComfyUI-ARG-Toolkit/web/docs/XExchange.md

ECDH Shared Key Exchange

Performs an X25519 or X448 Diffie-Hellman key exchange to derive a shared secret.

Source library: cryptography

Overview

This node performs an Elliptic Curve Diffie-Hellman (ECDH) key exchange using the X25519 or X448 curve. Given a private key and the other party's public key, it computes a shared secret that can be used to derive symmetric encryption keys. This is the foundational primitive for modern key exchange protocols.

Parameters

• key_source: How to obtain the private key.
  • Fresh Key: Generates a new random private key.
  • From Private Bytes: Uses a previously serialized private key.
• key_type: The curve (x25519 or x448).
• public_key: The other party's public key, as a BYTESLIKE object. This is expected in Raw format (32 bytes for x25519, 56 bytes for x448).
• private_key: (Optional) The serialized private key bytes. Required when key_source is "From Private Bytes".

Outputs

• shared_key: The derived shared secret, as a BYTESLIKE object. This is a 32-byte (x25519) or 56-byte (x448) value that should be passed through a Key Derivation Function (KDF) before use as an encryption key.

Additional Considerations

• Never reuse a private key with multiple parties. Each key pair should be used for a single exchange.
• The shared secret itself is not a suitable encryption key. Always pass it through a KDF (e.g., HKDF, ConcatKDF) with appropriate context information.
• X25519 does not provide authentication by itself. Combine it with a digital signature scheme (e.g., Ed25519) to prevent man-in-the-middle attacks.
• The public key input expects Raw format. If you have a serialized public key in PEM or DER format, use the appropriate loader node first.