RE: Generating Unique Initialization Vectors

[Søren Dreijer]

Jeff,
 
Thanks for the swift reply!
 
Currently I just use GenerateBlock() to generate the entire random sequence in one go instead of calling GenerateByte() continually.

Speaking of which, I'm not really sure what blocking means compared to nonblocking?
 
I guess using the library on other systems than Windows does not guarantee a unique IV. Do you know how the autoseeding function works? Does it take things such as time into account to minimize collisions?
Also, does using MCP guarantee a unique random value each time? I know the API provides such a function but I don't know if Crypto++ uses it. If it doesn't it would probably be better to wrap your own random generator on Windows which actually uses that function..

Cheers!

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> Date: Mon, 4 Sep 2006 19:54:04 -0400
> From: [EMAIL PROTECTED]
> To: cryptopp-list@eskimo.com
> Subject: Re: Generating Unique Initialization Vectors
>
> Hi Soren,
>
> Sorry, I should have gone into more detail.
>
> > What is the best approach to generating unique initialization vectors for
> > block ciphers such as AES in CFB mode?
> I would personally use the Crypto++ RNG. There are better ways to
> generate, rather than going for 1 byte at a time.
>
>     CryptoPP::AutoSeededRandomPool rng;
>
>     std::string Key( "BYTE key[ CryptoPP::AES::DEFAULT_KEYLENGTH ]
> =\r\n    { " );
>     std::string   IV( ("BYTE  iv[ CryptoPP::AES::BLOCKSIZE ] =\r\n    { " );
>
>     //
>     // IV
>     //
>     for( INT i = 0; i < CryptoPP::AES::BLOCKSIZE; i++ ) {
>
>         BYTE b = rng.GenerateByte();
>         ...
>
>     }
>
> > How does AutoSeededRandomPool work? Is it guaranteed
> > not to return the same number twice?
> Gleaned from osrng.cpp:
> if Not WIN32
>    Nonblocking RNG:  /dev/urandom
>    Blocking RNG:  /dev/random
>
> If WIN32
>     Use Microsoft Cryptographic Provider
>
> IIRC, MCP uses an OS derived value, stored in the registry (this is
> for NT systems, not 9x systems)
>
> Jeff
>
> On 9/4/06, Søren Dreijer <[EMAIL PROTECTED]> wrote:
> >
> > Yes, I know how you use it but I don't see anything about how to use it to
> > generate a unique IV..
> >
> > ________________________________
> > > Date: Mon, 4 Sep 2006 17:27:38 -0400
> > > From: [EMAIL PROTECTED]
> > > To: cryptopp-list@eskimo.com
> > > Subject: Re: Generating Unique Initialization Vectors
> >
> > >
> > > Hi Soren,
> > >
> > > > > How does AutoSeededRandomPool work?
> > >
> > http://www.eskimo.com/~weidai/cgi-bin/fom-serve/cache/83.html
> > >
> > > Jeff
> > >
> > > On 9/4/06, Søren Dreijer <[EMAIL PROTECTED]> wrote:
> > > >
> > > > Hey,
> > > >
> > > > What is the best approach to generating unique
> > initialization vectors for
> > > > block ciphers such as AES in CFB mode?
> > > >
> > > > How does AutoSeededRandomPool work? Is it guaranteed
> > not to return the same
> > > > number twice?
> > > >
> > > > - Soren
> > > >
> > > > ________________________________
> > > > Call friends with PC-to-PC calling -- FREE Try it now!
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> >
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