new

static VALUE
ossl_hmac_initialize(VALUE self, VALUE key, VALUE digest)
{
    HMAC_CTX *ctx;

    StringValue(key);
    GetHMAC(self, ctx);
    HMAC_Init_ex(ctx, RSTRING_PTR(key), RSTRING_LEN(key),
                 GetDigestPtr(digest), NULL);

    return self;
}