[Ur] Encrypted cookies or hashed values

[Adam Chlipala]

Taru Karttunen wrote:
> I created a small library[1] for captchas and am trying to set secret
> values in cookies. Are there either seeded hash functions or encrypted
> cookies available?
>    

The standard crypt() function is in [Basis], but that's it for bits 
exported by default to Ur ATM.  OpenSSL is linked with every 
application, so there are plenty of useful functions available to wrap 
with the C FFI.