[jira] [Reopened] (CAY-1925) cayenne-crypto: add optional compression to the encryption pipeline

["Andrus Adamchik (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CAY-1925?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Andrus Adamchik reopened CAY-1925:
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(actually reopening - we need to add logic to skip gzip on small values)

> cayenne-crypto: add optional compression to the encryption pipeline
> -------------------------------------------------------------------
>
>                 Key: CAY-1925
>                 URL: https://issues.apache.org/jira/browse/CAY-1925
>             Project: Cayenne
>          Issue Type: Bug
>            Reporter: Andrus Adamchik
>            Assignee: Andrus Adamchik
>             Fix For: 3.2.M2
>
>
> This is about transparently compressing encrypted data. Compression can be optionally enabled via CryptoModuleBuilder. By default we'll use GZIP compression, but as with everything in cayenne-crypto, this is a pluggable strategy.  
> If compression is enabled, we should distinguish between small and large values. For small values compression only adds overhead and should be skipped. Per  [1] Google recommends not compressing files smaller than 150 - 1000 bytes (this is of course for the web content). We'll use an internal threshold somewhere in this range, and then we should just do some performance tests.
> Compression will happen *before* encryption, as it is likely to be more efficient on plaintext than randomized encrypted data [2]. 
> We'll need to add compression flag to the "header" block of the ciphertext. To do that we'll reorganize the header to allow storing more data, and expand dynamically as needed:
> * byte 0..2: "magic" number identifying the format as Cayenne-crypto encrypted sequence.
> * byte 3: header length N, i.e. how many bytes the header contains, including magic number and the length indicator. N can be 0..127.
> * byte 4: a bit String representing various flags, such as compression.
> * byte 5..N: UTF8-encoded symbolic name of the encryption key.
> [1] https://developers.google.com/speed/docs/best-practices/payload#GzipCompression
> [2] http://superuser.com/questions/257782/compress-and-then-encrypt-or-vice-versa



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