deriveKey

ubyte[] deriveKey(const(ubyte)[]  sharedSecretMpint,
       in  ubyte[32]  exchangeHash,  in  ubyte[32]  sessionId,
       char  letterOne,  size_t length)

Derives directional key material with the SSH KDF.

K1 = HASH(K || H || letter || session_id) and Kn = HASH(K || H || K1 || ... || Kn-1) until length bytes exist; sharedSecretEncoded supplies the wire-encoded shared secret (raw bytes in a length-prefixed string, matching the deployed curve25519 behaviour).

Parameters

`sharedSecretMpint`	The wire-encoded shared secret K.
`exchangeHash`	The exchange hash H.
`sessionId`	The session identifier.
`letterOne`	KDF selector byte, `'A'` through `'F'`.
`length`	Number of bytes required.

Returns

The derived key material.