No, it's actually 521. I had some people helpfully trying to "correct" this to 512 in the past, it's a common attitude when seeing this for the first time ;) See for reference section G.1.4 page 58:
https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-186-draft.pdf
"The modulus for this curve is p = 2^521 – 1".Daniel J. Bernstein actually regards the 521 curve as the only secure NIST curve, asserting that the 256 and 384 curves have too many suspicious and unexplained terms.
"To be fair I should mention that there's one standard NIST curve using a nice prime, namely 2^521 – 1; but the sheer size of this prime makes it much slower than NIST P-256."
Oh, that's weird. Sorry. As it went 256 384 I thought it was 512 intuitively.
Re:OpenSSH 8.4
by Denvercoder9 on Monday September 28, 2020 @02:31AM
(#24613583)
No, surprisingly that curve is actually called NIST P-521.
It says "The RFC5656 ECDSA algorithms: ecdsa-sha2-nistp256/384/521." I think the last bit should be 512, not 521.