crypto/des: show example of 16-byte key

[gopherbot]

by visan.ovidiu:

Which operating system are you using?
Ubuntu 11.10

Which version are you using?  (run 'go version')
go version go1

Please provide any additional information below.

NewTripleDESCipher should accept as minimum a 16 byte length key and as maximum the
current 24 byte lenght key.
Also it should take the initialization vector (IV) as parameter.

eg. http://msdn.microsoft.com/en-us/library/system.security.cryptography.tripledes.aspx

[rsc]

Comment 1:

This amounts to not supporting DES-EDE2, only DES-EDE3
+agl for an opinion on whether we want to do that.
It is unclear to me - it appears that Java does not support it either,
and it is trivial for clients who want to use less key to expand it
before using our 3DES.

Labels changed: added priority-later, removed priority-triage.

Status changed to Thinking.

[agl]

Comment 2:

An IV can only apply to a cipher mode, not a cipher. So that's moot here.
A patch to expand a 128-bit key internally would be pretty simple. But I think I'd still
want to see some evidence that something in the real world is actually using EDE2.

[gopherbot]

Comment 3 by visan.ovidiu:

As an example, sometimes i have to take some code written in C# and have the pleasure to
write it in Go. The problem here is that the C# code it's using a 16 byte key and the
encrypted text it's in a file, and i wanted to decrypt that using Go.
 
Thanks for the short reply (considering the amount of work you have).

[gopherbot]

Comment 4 by visan.ovidiu:

Thanks for the short reply (considering the amount of work you have). 
As an example, sometimes i have to take some code written in C# and have the pleasure to
write it in Go. The problem here is that the C# code it's using a 16 byte key to decrypt
an existing text that's in a file, and i wanted to decrypt that text using Go.

[rsc]

Comment 5:

Just in case it's not clear, the workaround here is to use
func key16to24(key []byte) []byte {
    var b []byte
    b = append(b, key[:16]...)
    b = append(b, key[:8]...)
    return b
}
to convert your 16-byte key into the equivalent 24-byte key.
Russ

[agl]

Comment 6:

As rsc points out, the workaround is easy. If lots of people will be using it then it's
worth putting in the standard library. However, DES-EDE2 is very obscure and it might
well be that you're the only person who needs it. In that case, it's obviously better if
you carry the code yourself.

[gopherbot]

Comment 7 by visan.ovidiu:

Thank you very much Russ!
It worked flawlessly, thanks taking time for this.
More small examples like this would help lots of newcomers to Go.
Thanks again!

[rsc]

Comment 8:

Let's put this into a godoc example somewhere and call it done.

Status changed to Accepted.

[gopherbot]

Comment 9 by visan.ovidiu:

thanks, it might help others too

[rsc]

Comment 10:

Labels changed: added go1.1.

[rsc]

Comment 11:

Labels changed: added size-s.

[rsc]

Comment 12:

Labels changed: added suggested.

[agl]

Comment 13:

This issue was closed by revision 8f1d170.

Status changed to Fixed.