I am not a cryptographer, but can explain that Magic Wormhole uses SPAKE2 to negotiate a shared secret (RFC9382 claims equivalent to gap Diffie-Hellman), and then uses NaCl SecretBox to symmetrically encrypt all data between the peers.

(If using the newer Dilation protocol -- which is true for many of the non-file-transfer tools like ShWiM, Git-WithMe or Fowl -- peer traffic uses this shared secret with Noise, specifically "Noise_NNpsk0_25519_ChaChaPoly_BLAKE2s")

One tool that does now use Magic Wormhole for "introduction" like this is EtherSync: https://ethersync.github.io/ethersync/