sect233r1 (NIST B-233) is a pseudo-random curve over the binary field GF(2^233); NIST has deprecated it.
sect233r1 is a binary Weierstrass curve y² + xy = x³ + ax² + b over the binary field GF(2^233) with a 233-bit prime-order subgroup and cofactor 2; its estimated security level is 112 bits. Status: deprecated, do not use for new keys.
sect233r1 is y² + xy = x³ + x² + b over GF(2^233) with the reduction polynomial f shown above; b was derived from the listed seed with SHA-1 (ANSI X9.62). The group has cofactor 2 and about 112 bits of security.
FIPS 186-2 to 186-4 listed it as B-233. NIST SP 800-186 (2023) deprecates every curve over a binary field, and RFC 8422 deprecated them for TLS. OpenSSL can be built without binary-curve support (no-ec2m).