[cm/prv/] with Streamlined NTRU Prime 761 + X25519.
=> https://ntruprime.cr.yp.to/ NTRU Prime
=> https://datatracker.ietf.org/doc/html/rfc7748.html X25519
It is a concatenation of SNTRUP's 1763-byte and X25519's 32-byte keys.
"sntrup761-x25519" algorithm identifier is used.
