The NIST P-256 base field prime.
The NIST P-256 base field prime is the characteristic of the finite field
over which the Weierstrass elliptic curve
The curve
The prime is computed as:
2^256 - 2^224 + 2^192 + 2^96 - 1
SEC 2: Recommended Elliptic Curve Domain Parameters (Section 2.4.2) calls it
0xffffffff00000001000000000000000000000000ffffffffffffffffffffffff