def METHOD_NAME(pubkey_theirs, privkey):
    """Compute X coordinate of shared ECDH point between ellswift pubkey and privkey."""
    u = FE(int.from_bytes(pubkey_theirs[:32], 'big'))
    t = FE(int.from_bytes(pubkey_theirs[32:], 'big'))
    d = int.from_bytes(privkey, 'big')
    return (d * GE.lift_x(xswiftec(u, t))).x.to_bytes()