Multiple (mostly crypto) Improvements

[Jack64]

Hi guys,

Great job on the SCP 👍 I did find a couple of issues on the crypto side of it, so here's a PR with my suggested changes.

Best regards, João

CHANGELOG: Authentication and password management - Validation and Storage:

• Fixed typos and changed conceptual phrasing for clarity
• Added uniqueness requirement for salts
• Fixed the crypto adage :)

Cryptographic Practices:

• Fixed typos and changed conceptual phrasing for clarity
• Terminology matters: I suggest (but did not implement) a global change in the document from hash to KDF (Key Derivation Function) whenever referring to a function that takes as input a user-supplied password to derive a hash or encryption key ( Argon2,scrypt,bcrypt,etc. ); and using hash when talking about the hash primitive functions ( SHA, BLAKE, etc. ) or their output only. This prevents a lot of confusion for first-time readers.
• Changed SHA-256 to BLAKE2 as it is the most modern, secure, flexible and fast hashing algorithm at the moment
• Added small explanation about cipher modes
• Added small explanation about public key cryptography
• Added reference to NaCl/box and NaCl/secretbox (libsodium)
• SHA-1 is not broken per se, that would mean a break of its second pre-image resistance, which is not the same as the collision breakthrough by the Google team earlier this year -- that being said, it's still time to stop using it, so let's just call it "deprecated".

PRNGs:

• Fixed typos and changed conceptual phrasing for clarity
• Added explanation of what the Seed is
• Fixed terminology: all software random number generators are pseudo-random number generators -- for true randomness one need would need a hardware source.

[PauloASilva]

Hi @Jack64, first of all, thanks for your contribution.

We're following Vincent Driessen's successful branching model as described on How To Contribute section. Because of that, pull requests should be opened to our develop branch from a (feature) branch on your own fork repository.

Right now our develop branch already has multiple fixes and community contributions ready to be released, what will happened soon.

Can o please submit your changes to our develop branch?

Regards, Paulo A. Silva

[Jack64]

Yes of course, let me close this and re-PR correctly :)