Does Signal Application use Eliptic Curve cryptography for encryption as well? I am studying how Signal application works and as I was reading the documentation on how is applied the XEdDSA and VXEdDSA Signature Schemes.

But I kept wondering: if Signal uses elliptic curve for signing a message (as far as I understood), then how does it apply cryptography for encrypting the actual voice and instant messages. Does it use an eliptic curve cryptography scheme with a different key besides the other one?
Signal Double Rachet and X3DH protocols for key initialization and session/temptorary encryption key generation. Whilst the XEdDSA and VXEdDSA are used for signing.

All of the schemes are based on X25519 and X448 curves.