if C._goboringcrypto_HMAC_Init(&h.ctx, unsafe.Pointer(base(h.key)), C.int(len(h.key)), h.md) == 0 {
		panic("boringcrypto: HMAC_Init failed")
	}
	if int(C._goboringcrypto_HMAC_size(&h.ctx)) != h.size {
		println("boringcrypto: HMAC size:", C._goboringcrypto_HMAC_size(&h.ctx), "!=", h.size)
		panic("boringcrypto: HMAC size mismatch")
	}
	runtime.KeepAlive(h) // Next line will keep h alive too; just making doubly sure.
	h.sum = nil