52 lines
2.7 KiB
Markdown
52 lines
2.7 KiB
Markdown
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Frequently Asked Questions
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===========================
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How do I use this library to encrypt passwords?
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------------------------------------------------
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Passwords should not be encrypted, they should be hashed with a *slow* password
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hashing function that's designed to slow down password guessing attacks. See
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[How to Safely Store Your Users' Passwords in
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2016](https://paragonie.com/blog/2016/02/how-safely-store-password-in-2016).
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How do I give it the same key every time instead of a new random key?
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----------------------------------------------------------------------
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A `Key` object can be saved to a string by calling its `saveToAsciiSafeString()`
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method. You will have to save that string somewhere safe, and then load it back
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into a `Key` object using `Key`'s `loadFromAsciiSafeString` static method.
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Where you store the string depends on your application. For example if you are
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using `KeyProtectedByPassword` to encrypt files with a user's login password,
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then you should not store the `Key` at all. If you are protecting sensitive data
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on a server that may be compromised, then you should store it in a hardware
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security module. When in doubt, consult a security expert.
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Why is an EnvironmentIsBrokenException getting thrown?
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-------------------------------------------------------
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Either you've encountered a bug in this library, or your system doesn't support
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the use of this library. For example, if your system does not have a secure
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random number generator, this library will refuse to run, by throwing that
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exception, instead of falling back to an insecure random number generator.
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Why am I getting a BadFormatException when loading a Key from a string?
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------------------------------------------------------------------------
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If you're getting this exception, then the string you're giving to
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`loadFromAsciiSafeString()` is *not* the same as the string you got from
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`saveToAsciiSafeString()`. Perhaps your database column isn't wide enough and
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it's truncating the string as you insert it?
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Does encrypting hide the length of the plaintext?
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--------------------------------------------------
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Encryption does not, and is not intended to, hide the length of the data being
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encrypted. For example, it is not safe to encrypt a field in which only a small
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number of different-length values are possible (e.g. "male" or "female") since
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it would be possible to tell what the plaintext is by looking at the length of
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the ciphertext. In order to do this safely, it is your responsibility to, before
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encrypting, pad the data out to the length of the longest string that will ever
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be encrypted. This way, all plaintexts are the same length, and no information
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about the plaintext can be gleaned from the length of the ciphertext.
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