Ipsec Tunnel problem

Hey everyone,

Currently, I'm dealing with a situation where I have two sites, one equipped with a Fortigate firewall and the other with pfSense. My goal is to establish an IPsec tunnel between them. However, the version of Fortigate I'm working with is 7.0.12, which only supports the DES encryption algorithm. Additionally, for authentication, we only have SHA-256, 384, and 512 available.

On the other hand, pfSense supports different encryption algorithms. Given these limitations and the requirement to maintain the current version of Fortigate without updates, what would be the best solution to address this issue?

Thanks in advance for any insights or recommendations you can provide.

PS: It's crucial that we maintain the current version of Fortigate and cannot update it