use crypto/rand package instead of math/rand

[damien-white]

Reference issue: #289

There is a small mistake that has potentially big security-related consequences. I replaced the "math/rand" package in aead.go to "crypto/rand".

This PR fixes issue #289 as "crypto/rand" is a more secure solution and the package that is officially advised by the Go core team. It produces a stronger random number or psuedo-random number and is a more secure solution than "math/rand". This PR fixes the issue and should be easy to merge as only 2 lines are changed and they are both inside of the imports array (the replacement plus the sorting of imports added a line to the diff).

I looked to see if you had any contributing guidelines as I would love to help contribute further to this project. Fantastic work with everything so far. I love it. 👍

[dils2k]

LGTM

[NHAS]

I just want to note, that while this is a good start, it doesnt remediate the full issue.

As noted in here: #289

Just using a properly random source would require the rotation of keys every 2^32 messages.

The best and complete solution would implement a repetition resistant nonce algorithm details of which I've noted here #289 (comment)

[damien-white]

Thank you @NHAS.

All great and valid points. I will look into revising my PR and see if I can come up with something that satisfies these contraints and solves the issue. I think everyone would agree that using the best, most complete solution would be the most ideal way of handling this.

My apologies, I have been away for the past few days. I will get right on it!

[NHAS]

Thats totally fine! Merging the change as it currently is, is a step in the right direction for sure.

I've actually started writing my own solution to it as well, so I'd be interested to see what we both come up with.

[damien-white]

You work looks really great. Wow. You really got a lot done in a short time. Some of the function renaming adds a few extra lines to the diff but overall, I personally think that the functions (renamed) still make complete sense, the code is clear and it looks good to me.

I don't have any personal say but I am very impressed. Great work. 👍

[NHAS]

Thank you! I've actually just spotted a small issue with it. So I'll give that a patch