---
title: Strong TLS certificates with acme.sh
subtitle: 384-bit of https
lang: en
slug: "acme-sh-tls-cert"
createdAt: "2022-06-08T14:24:06.000Z"
excerpt: Real cert have curves.
tags: ["security"]
type: snippets
---

## Disclaimer

I'm, in absolutely no regards, a security expert. I just fancy shiny new things of the interwebs.  
This is why I've switched my default TLS certificates to use elliptic curve cryptography (ECC) instead of RSA. Now I have a sweet 100/100 on [tls.imirhil.fr](https://tls.imirhil.fr/)

You can learn (far) more by reading [this topic](https://crypto.stackexchange.com/questions/1190/why-is-elliptic-curve-cryptography-not-widely-used-compared-to-rsa) and its linked resources.

## Requirements

### Installing acme.sh

For automation and ease of use purposes, I'm using [acme.sh](https://github.com/acmesh-official/acme.sh)

```bash
# for using standalone mode, you might have to install as sudo
curl https://get.acme.sh | sh -s email=mail@domain.tld
```

### Changing default authority

By default, acme.sh uses ZeroSSL to sign certificates. We need to change this to Let's Encrypt because according to acme.sh, they're the only ones offering ECC capabilities.

```bash
acme.sh --set-default-ca --server letsencrypt
```

## Using your DNS api

If available, the easiest way to issue a certificate is to use the DNS api of your DNS provider. acme.sh supports [a lot](https://github.com/acmesh-official/acme.sh/wiki/dnsapi) of DNS providers.

### Define an api key

Follow the [docs](https://github.com/acmesh-official/acme.sh/wiki/dnsapi) for your DNS provider, usually:

```bash
export PROVIDER_Key="YOUR_API_KEY"
```

### Issue the cert

```bash
acme.sh --issue -d domain.tld --dns dns_provider --keylength ec-384
```

## Using standalone mode

If you don't have access to the DNS provider, we can use the standalone mode to spin up a temporary web server that will handle all the verifications.

Port `80` must be free.

```bash
acme.sh --issue --standalone -d domain.tld --keylength ec-384
```

## Examples

### Multi domains standalone

```bash
acme.sh --issue --standalone -d domain.tld -d www.domain.tld -d subdomain.domain.tld --keylength ec-384
```

### Wildcard domain DNS

```bash
acme.sh --issue -d domain.tld -d '*.domain.tld' --dns dns_provider --keylength ec-384
```

## Next steps

The ECC certificate alone will not grant you a high/perfect score.

### TLS version

Limit TLS version to 1.2 and 1.3 (or just 1.3 as there is only a [5% compatibility gap](https://caniuse.com/?search=tls%201.) with 1.2).

### HSTS

Use the [strict transport security](https://scotthelme.co.uk/hsts-the-missing-link-in-tls/) header.

```
Strict-Transport-Security: max-age=31536000; includeSubDomains
```

### Cipher suite

Use recent and strong ciphers. This is where my knowledge hits its limit… I'm having a really hard time understanding what to use and why.

I've based my initial choices of ciphers on [this list](https://tls.imirhil.fr/ciphers), cross referencing it with (older?) [browser compatibility](https://tls.imirhil.fr/suite).

I then asked [Aeris](https://twitter.com/aeris22), the creator of [tls.imirhil.fr](https://tls.imirhil.fr), about it and he advised me to use the following:

```
ECDHE+AES:ECDHE+CHACHA20
```

In order to achieve a perfect score, we can be a little more restrictive with:

```
ECDHE+AES256:ECDHE+CHACHA20
```