Frequently Asked Questions
===========================

How do I use this library to encrypt passwords?
------------------------------------------------

Passwords should not be encrypted, they should be hashed with a *slow* password
hashing function that's designed to slow down password guessing attacks. See
[How to Safely Store Your Users' Passwords in
2016](https://paragonie.com/blog/2016/02/how-safely-store-password-in-2016).

How do I give it the same key every time instead of a new random key?
----------------------------------------------------------------------

A `Key` object can be saved to a string by calling its `saveToAsciiSafeString()`
method. You will have to save that string somewhere safe, and then load it back
into a `Key` object using `Key`'s `loadFromAsciiSafeString` static method.

Where you store the string depends on your application. For example if you are
using `KeyProtectedByPassword` to encrypt files with a user's login password,
then you should not store the `Key` at all. If you are protecting sensitive data
on a server that may be compromised, then you should store it in a hardware
security module. When in doubt, consult a security expert.

Why is an EnvironmentIsBrokenException getting thrown?
-------------------------------------------------------

Either you've encountered a bug in this library, or your system doesn't support
the use of this library. For example, if your system does not have a secure
random number generator, this library will refuse to run, by throwing that
exception, instead of falling back to an insecure random number generator.

Why am I getting a BadFormatException when loading a Key from a string?
------------------------------------------------------------------------

If you're getting this exception, then the string you're giving to
`loadFromAsciiSafeString()` is *not* the same as the string you got from
`saveToAsciiSafeString()`. Perhaps your database column isn't wide enough and
it's truncating the string as you insert it?

Does encrypting hide the length of the plaintext?
--------------------------------------------------

Encryption does not, and is not intended to, hide the length of the data being
encrypted. For example, it is not safe to encrypt a field in which only a small
number of different-length values are possible (e.g. "male" or "female") since
it would be possible to tell what the plaintext is by looking at the length of
the ciphertext. In order to do this safely, it is your responsibility to, before
encrypting, pad the data out to the length of the longest string that will ever
be encrypted. This way, all plaintexts are the same length, and no information
about the plaintext can be gleaned from the length of the ciphertext.

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• [F] FAQ.md
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• [F] InternalDeveloperDocs.md
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