Variable length string prefixes could lead to injection attack

[jtremback]

I'm not 100% sure about this, but I think that the way we are using variable length string prefixes in the CCV module (for example: https://github.com/cosmos/interchain-security/blob/main/x/ccv/child/types/keys.go) could lead to a situation where an injection attack is possible.

Think about the (contrived) scenario where you have one set of record with keys made like this: "bond" + <ID> and a set of records with keys made like this "bonded" + <ID>. If the user has some kind of control over the ID on the "bond" records, they could create a situation where the first bytes of the ID are the same as the letters "ed". This could allow them to insert records into the "bonded" set.

I think we should use byte prefixes as is done in cosmos-sdk modules, or use iota to generate byte prefixes (we did this in gravity). Another option is to take string prefixes but hash or pad them.

[jtremback]

I see we use these with a separator (which should alleviate the issue) in some places but not all