What are memos?
When Ravencoin was being conceived, one of the goals was to fix all the problems in BTC+Counterparty/OpenAssets. Among those problems was that the meta-data, which is just information about the token, went missing. Why? It was up to the token issuer to hold it forever on a website. A shortened URL to the website was all that went on-chain. These websites would disappear and all that was left was useless and informationless bitly URLs that all looked the same.
The solution used for Ravencoin was to put the meta-data in IPFS (InterPlanetary File System). If you don’t know what that is, then you’re in for a treat. They can describe it better, but the easiest way to think about it is to imagine that BitTorrent and DropBox had a baby. That baby is IPFS. IPFS lets you chuck any file, or even a directory full of files, into IPFS and get back a hash. This hash (IPFS Content Id) is the reference to the file. It can’t change. Why? Because then it wouldn’t reference the file, or if the file changed, the content would have a different hash. This two-way linkage is critical for how Ravencoin uses IPFS.
The hash (Content Id) is embedded into the Ravencoin blockchain when you create an asset. The embedded hash can never change because… well… blockchain. And the content can never change because any change in content and then the hash doesn’t reference…