cipher: Decrypt data even if mac is wrong

This is required to prevent timing attack.
Optimize conversion from u64 to bytes
Make use of iterators
Make use of mem::replace() and cmp::min()
Merge pull request #1 from Florob/idiomatic

Make some code more idiomatic
Update for language changes
(WIP) DER parser for x509 certification

(this does not try to implement complete ASN.1/DER spec)
(WIP) incomplete x509 certification parser
bump
tmp