Careful. Openssl enc is basically a poor toy example, it's not a robust authenticated encryption tool for real world use.
It explicitly doesn't support modern AEAD ciphers or even a simple MAC (so the ciphertext can be silently tampered with - note anyone who can do that can also replace your par2 files), and it doesn't use a robust key derivation algorithm for password use (single-round of a hash, basically, default MD5 - about as weak as it comes).
hpenc looks like a nice high performance modern alternative: https://github.com/vstakhov/hpenc
That's the key and that's why it's here. It's a very, very stretched analogy, but from the very beginning, we at rsync.net have tried to run rsync.net itself as a unix primitive.
After already supporting actions like this, for years:
ssh [email protected] sha256 some/file
ssh [email protected] s3cmd get s3://rsync/mscdex.exe
mysqldump -u mysql db | ssh [email protected]"dd of=db_dump"
Really, with stdin/stdout the sky is the limit, and there are minimal ties to any specific service since only the most generic raw cloud storage features are being used.