A simple implementation of HMAC DRBG (Deterministic Random Bit Generator) for Solana
DRBG is used in RFC6979 for deterministic nonce generation.
Please note that DRBG alone is not the full implementation of RFC6979, as a valid nonce would also need to clamped within the finite field of the curve you are using for ECDSA. For the full implementation of RFC6979, check out solana-rfc6979.
let privkey: [u8;32] = [0xc9, 0xaf, 0xa9, 0xd8, 0x45, 0xba, 0x75, 0x16, 0x6b, 0x5c, 0x21, 0x57, 0x67, 0xb1, 0xd6, 0x93, 0x4e, 0x50, 0xc3, 0xdb, 0x36, 0xe8, 0x9b, 0x12, 0x7b, 0x8a, 0x62, 0x2b, 0x12, 0x0f, 0x67, 0x21];
let message_hash: [u8;32] = [0xaf, 0x2b, 0xdb, 0xe1, 0xaa, 0x9b, 0x6e, 0xc1, 0xe2, 0xad, 0xe1, 0xd6, 0x94, 0xf4, 0x1f, 0xc7, 0x1a, 0x83, 0x1d, 0x02, 0x68, 0xe9, 0x89, 0x15, 0x62, 0x11, 0x3d, 0x8a, 0x62, 0xad, 0xd1, 0xbf];
let mut result = [0u8;32];
HmacDrbg::new(&privkey, &message_hash).fill_bytes(&mut result); // Fills in result with resulting [u8;32]