Re: Obscuring an NSString
Re: Obscuring an NSString
- Subject: Re: Obscuring an NSString
- From: Kyle Sluder <email@hidden>
- Date: Sun, 5 Dec 2010 20:41:55 -0800
On Dec 5, 2010, at 2:31 PM, Adam Gerson <email@hidden> wrote:
> Thanks to all who responded. Let me explain my situation a little
> better. I am storing several string values into an XML file. I want to
> obscure one of them. When I encrpyt the NSString to an NSdata I can
> store the data as a string in XML, however when I read the string back
> in I dont know how to convert it back to NSData to decrypt.
You'd better not be treating your XML data as an NSString. ;-)
As long as you store your data in a CDATA section, the XML API you're using should give you the ability to get the raw data for a node.
Alternatively, one of the convenient properties of Base64 is that it maps your data into a range of printable ASCII characters. So you can treat the Base64 data as ASCII and write it as a string in your XML document (being mindful, of course, of the document's encoding, which is most likely UTF-8 and therefore identical to ASCII for the Base64 output range). Then read it back in as a string, convert it to ASCII, and feed the raw ASCII data into the Base64 decoding algorithm.
So to maximize flexibility without involving CDATAs, here's the process I'd use:
Saving: Plaintext NSString --> Plaintext NSData (UTF-8; use -dataWithEncoding:) --> Base64 NSData (ASCII) --> Base64 NSString (use +stringWithData:encoding: to create this) --> your XML document
Loading: Your XML document --> Base64 NSString (UTF-16) --> Base64 NSData (ASCII characters; use -dataWithEncoding to get this) --> Plaintext NSData (UTF-16) --> NSString (again use +stringWithData:encoding:)
HTH,
--Kyle Sluder
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