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37 lines
1.7 KiB
Markdown
37 lines
1.7 KiB
Markdown
What is urcrypt?
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----------------
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urcrypt is a library of cryptography routines used by urbit jets.
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Why is urcrypt?
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---------------
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Urbit's C runtime (long the only urbit runtime) has accumulated a collection of
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cryptography dependencies, some with custom additions or patches. These
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libraries have different conventions and have been managed by u3 in an ad-hoc
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manner. Reproducing that arrangement in other runtimes is tricky and
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error-prone. The (sometimes inconsistent) logic must be reproduced and suitable
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cryptography primitives must be found (or worse, written) for the new
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environment.
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To ease these burdens, urcrypt isolates the quirks behind a consistent calling
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convention. Everything is a little-endian byte array, and each jetted operation
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has a corresponding function in the library. Jets simply unpack their nouns,
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call urcrypt, and pack the results.
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What is a cryptography routine?
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-------------------------------
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This is more of a subjective question than it might appear. Any of the following
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conditions are sufficient, but not necessary, for a function to be included in
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urcrypt:
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* The routine is sensitive to side-channel attacks (encryption, etc)
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* Some property of the routine is cryptographically useful (SHA, RIPE, etc)
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* The routine typically lives in a crypto library, for whatever reason.
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A word on OpenSSL
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-----------------
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Urcrypt depends on OpenSSL's libcrypto, which has global state. In order
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to avoid dealing with this state, urcrypt refuses to build with an internal
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libcrypto. Either build statically (pass `--disable-shared` to `./configure`)
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or provide a shared libcrypto for urcrypt to link against. It is the library
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user's responsibility to initialize openssl, set custom memory functions, etc.
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