HKDF_expand
if (!HKDF_expand(out_key, out_len, digest, prk, prk_len, info,
return HKDF_expand(key, *keylen, kctx->md, kctx->key,
int HKDF_expand(uint8_t *out_key, size_t out_len,
ret = HKDF_expand(out->data, out->len, digest, secret->data,