htd2007's Blog

星期二, 九月 04, 2007

Picross DS - FAQ/Puzzle Solutions (ZIP)

Sent to you by Hudong via Google Reader:

Picross DS - FAQ/Puzzle Solutions (ZIP)

via IGN Complete on Sep 03, 2007

Picross DS (DS)
Picross DS, Nintendo DS

Things you can do from here:

Visit the original item
on IGN Complete
Subscribe to IGN Complete using Google Reader
Get started using Google Reader to easily keep up with all your favorite sites

How to digitally sign a string

Sent to you by Hudong via Google Reader:

How to digitally sign a string

via MSDN Blogs by NicolD on Sep 03, 2007

The first step is to create a pair of key(pulic/private):

RSACryptoServiceProvider RSA = new RSACryptoServiceProvider();
string publicKey = RSA.ToXmlString(false);
string privateKey = RSA.ToXmlString(true);

Private key is required to sign the string. Public key is required to verify if the sign is valid or not.

Sequence required to create a sign is:

select a private key
select an HASH algorithm to create one starting from the string to sign (you'll sign the hash, not the string)
create a sign starting from the hash

As shown bellow:

RSACryptoServiceProvider RSA = new RSACryptoServiceProvider();
RSA.FromXmlString(privateKey);
RSAPKCS1SignatureFormatter RSAFormatter = new RSAPKCS1SignatureFormatter(RSA);
RSAFormatter.SetHashAlgorithm("SHA1");
SHA1Managed SHhash = new SHA1Managed();
byte[] SignedHashValue = RSAFormatter.CreateSignature( SHhash.ComputeHash(new UnicodeEncoding().GetBytes(stringToBeSigned)));
string signature = System.Convert.ToBase64String(SignedHashValue);

Sequence of operations needed to verify a signature is instead:

select the proper public key
select the HASH algorithm to create one starting from the string to be verified
veirfy the sign

as shown below:

RSACryptoServiceProvider RSA = new RSACryptoServiceProvider();
RSA.FromXmlString(publicKey);
RSAPKCS1SignatureDeformatter RSADeformatter = new RSAPKCS1SignatureDeformatter(RSA);
RSADeformatter.SetHashAlgorithm("SHA1");
SHA1Managed SHhash = new SHA1Managed();
if (RSADeformatter.VerifySignature( 
 SHhash.ComputeHash(new UnicodeEncoding().GetBytes(stringToBeVerified)),
 System.Convert.FromBase64String(signature))
 )
 {
 /// The signature is valid.
 }
else
 {
 /// The signature is not valid.
 }