Companion

MSE generator g = 2.

Size of public keys and the shared secret, in bytes (768 bits).

The MSE 768-bit prime P, identical to libtorrent's dh_prime (src/pe_crypto.cpp). This is the Diffie-Hellman prime from the BitTorrent MSE spec.

Create an exchange from an explicit secret (big-endian bytes, any length up to 96). Primarily for deterministic tests; the secret is reduced mod P implicitly by the exponentiation.

Create an exchange with a fresh random 96-byte secret (libtorrent's default constructor: aux::random_bytes then import_bits).