Comment by hexedpackets

We still need to add the format to our docs, but it's essentially:

prefix + base64(len_encode(metadata) + len_encode(key_tag) + aes_encrypt(data))

So definitely possible to decrypt it without JumpWire, if you have the keys. There are some pieces of metadata we add in that we could make optional if you want to reduce the resulting ciphertext size. That metadata adds a few extra bytes, but it doesn't grow with the data size.