Compress Guids by hashing in small data sets

I'm working on a mobile app and i want to optimise the data that it's receiving from the server (as JSON). There are 3 lists returned (each containing its own class of objects, the approximate list sizes are 50, 100 and 170). Each object has a Guid id and there is some re开发者_JAVA百科lation data for each object. E.g.:

o = { Id = "8f088552-5b24-4ba4-a6e5-8958c4353581",
      RelatedIds = ["19d2e562-0874-473f-8e05-7052e8defd9a", "615b4c47-199a-4f7d-8268-08ed43d9c891", ... ] }

Is there a way to compress these Guids to something sorter without storing an identity map? Perhaps using a hash function?

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You can convert the 16-byte representation of a GUID into a Base 64 string. However you didn't mention a programming language so we can't help further.

A hash function is not recommended here because hash functions are generally lossy.

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No. One of the attributes of (non-cryptographic) hashes is that they collide: hash(a) == hash(b) but a != b. They are a performance optimization in the case where you are doing a lot of equality checks and you expect many false results (because if hash(a) != hash(b) then a != b). A GUID->counter map is probably the best way to get smaller ids here.

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You can convert hex (base16) to base64, and remove all the punctuation. You should save 25% for using base64, and another 4 bytes for punctuation.

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Thinking about it some more i've realized that HTTP compression (if enabled) is probably going to compress that data well enough anyway, so it's not really worth the effort to compress data manually.