GC256D is a short Weierstrass curve y² = x³ + ax + b over a 256-bit prime field with a 256-bit prime-order subgroup and cofactor 1; its estimated security level is 128 bits. Status: secure, but regional or niche.
GC256D was defined for GOST R 34.10-2001 in RFC 4357 §11.4 and is kept as paramSetD by GOST R 34.10-2012 (RFC 9215). It is y² = x³ − 3x + 32858 over a 256-bit prime, with prime order.
Its parameters are also registered for key exchange as CryptoPro-XchB. TLS lists it as group GC256D with signature scheme gostr34102012_256d (RFC 9189, RFC 9367).
| Standard | Name |
|---|---|
| IANA TLS (RFC 9189) | GC256D |
| TC 26 | id-tc26-gost-3410-2012-256-paramSetD |
| RFC 4357 | id-GostR3410-2001-CryptoPro-C-ParamSet |
| RFC 4357 | id-GostR3410-2001-CryptoPro-XchB-ParamSet |
256-bit prime field · about 128-bit security