I have some very sensitive family files that I want to store in the cloud on multiple providers for maximal reliability and redundancy. It's essentially a large archive of all our family photos, documents, and confidential photos. I'll be needing them in about ~20 years, but I won't access them or update them during this interval. These files must not be accessed by anyone but myself.
I am skeptical about AES being able to last for that long, because there could be advances in cryptanalysis. Instead, I'm considering ChaCha20, because it's a modern cipher and was sought for by security engineers at Google.
Supposing that I encrypt all files offline, use a secure key (along with Argon2), and ensure integrity (Poly1305), will my data theoretically be able to last for that long (the best attacks on ChaCha20 only break 7 rounds)? If not, is there a possible cipher that could? There will only be one copy, preventing chosen-plaintext attacks.