pub fn secp521r1_params() -> CurveParams<9>Expand description
secp521r1 / NIST P-521 curve parameters (FIPS 186-4 §D.1.2.5).
y^2 = x^3 - 3*x + b over the Mersenne prime p = 2^521 - 1.
The only curve we ship with qlen not a multiple of 8 – see
CurveParams::qlen_bits and CurveParams::felem_bytes for
the implications on RFC 6979 byte lengths and SEC1 octet
encoding respectively.