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diff --git a/DESIGN.mkd b/DESIGN.mkd new file mode 100644 index 000000000..f1a800cba --- /dev/null +++ b/DESIGN.mkd @@ -0,0 +1,54 @@ +# Design Notes on Open-Keychain + +This document contains notes on the software design of open keychain. + + +## Database design + +The database has two distinct types of tables: +- The key\_ring\_{public,secret} tables, which hold binary blobs of all known + public and private keys, respectively, and nothing else. +- All other tables, which cache information about key rings in a consistent + manner. This information includes various pieces of metadata about each key's + subkeys, user ids, and certificates. + +### Constraints + +All tables in the database have FOREIGN KEY constraints related to the +key\_ring\_public table. This is also true for the key\_ring\_secret table, +which means that secret keys cannot exist in the database without their public +key counterparts. This has implications in particular on the order of insertion +for private key rings and their public key ring counterparts into the database, +even more so when editing a key ring is edited. + +### Cache usage considerations + +It is of note that extraction of metadata from key rings is in some cases a +surprisingly expensive operation. As a prime example (heh), properly extracting +a key's associated primary user id requires examination and possibly +verification of all self-certificates, which in turn requires examination of +all certificates. + +To ensure consistency, each type of metadata must be extracted one way in +exactly one routine. For this reason, it is often desirable to make use of +cached data even when the underlying pgp key ring objects are contextually +available. + + +## Further work / WIP + +### Separation of concerns + +Roughly speaking, the crypto code should be strictly separated from the android +code. At the time of this writing (30.04.14), most of these thoughts are yet to +be put into practice. + +There are three aspects to OK which should be kept largely separate: +- Firstly, there is Code dealing with pgp and crypto. This code exclusively makes + use of the BouncyCastle library. It lives in the .pgp package. +- Secondly, there is code dealing with user interface and system integration, + which makes exclusive use of Android classes. +- Between these, there is glue code that is responsible for mapping pgp objects + to the database, and calling methods provided by the crypto code from the ui + code. + |