??Difference Between utf8encoder.GetBytes and Encoding.ASCII.GetBytes

[Phil C.]

Hi. (Using VB.Net) I have a symmetric encryption key stored as text,
encrytped by DPAPI in my web config that I use a handler
class to decrypt by the DPAPI and pass to the class that does the
encryption/decryption.
The decrypted DPAPI key is a string and needs to be converted to a byte
array for use by the encryption/decryption class. I'm confused as to the
difference using utf8encoder.GetBytes() or Encoding.ASCII.GetBytes() to do
this.

Thanks,

Phil
Boston, MA

 

[Joe Kaplan \(MVP - ADSI\)]

Generally speaking, the different encoding classes will give you an array of
bytes from a string corresponding to how that encoding actually represents a
string. Unicode (UTF16) represents each character as 2 bytes. UTF8 will
use a variable number of bytes for each character, but uses only one for
ASCII characters, so it generally uses much less space to store the same
Unicode data.

ASCII converts characters into a single byte using only 7 bits of each byte.
Since it only supports ASCII characters, it can result in data loss if the
string in question contains non-ASCII characters. It rarely has a use in
..NET crypto since strings are unicode in .NET.

If your encryption key is stored as text, it is probably stored in Base64.
In that case, you probably want to use Convert.FromBase64String to convert
the string key into a byte array.

Joe K.

 

[Phil C.]

Thank you Joe, you saved me a lot of grief.
However, then, what is the difference between UTF8Encoding.GetBytes("text")
and Encoding.Unicode.GetBytes("text)
or the converse
UTF8Encoding.GetString(Byte())
Encoding.Unicode.GetString(Byte())
??

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[Joe Kaplan \(MVP - ADSI\)]

The easiest thing to do is to write some code to test it and see, but I'll
try to explain too.

UTF8 and Unicode (which is really UTF16 as an encoding) are just two
different ways to create a binary encoding of a unicode string. UTF8 uses a
variable number of bytes for each character (depending on the character) and
UTF16 will use 2 bytes for each character. Since you test string, "test",
is all ASCII characters, the UTF8 version will be 4 bytes and the same as
the ASCII version. The Unicode version will be 8 bytes. To see differences
between ASCII and UTF8, you need to use non-ASCII characters in your test.

The various static/shared properties on the Encoding classes are just
shortcuts to keep you from having to build a new instance of the encoding
class. Generally, it will always be a little faster to just use them:

Encoding.UTF8
Encoding.Unicode

HTH,

Joe K.

 

[Phil C.]

Thanks Joe,
It's the usual "too many ways of doing something" make things more complex.