Understanding digital signature

Question

i generate certificate "test.cer" using java keytool ? as i understand , test.cer contains PublicKey and PrivateKey.
So i can import that Keys for digital signature.
so why i need
KeyPairGenerator keyGen = KeyPairGenerator.getInstance( "DSA" );
keyGen.initialize( 1024 );
KeyPair pair = keyGen.generateKeyPair();
PrivateKey privateKey = pair.getPrivate();
PublicKey publicKey = pair.getPublic();
Thanks

Answer 1

Rashad.Cahangirov wrote:
step 1) C:\Documents and Settings\User>keytool -genkey -alias MyCertificate
step 2) C:\Documents and Settings\User>keytool -certreq -alias MyCertificate -file myRequest.cer
Enter keystore password: test123456
step 3) C:\Documents and Settings\User>keytool -export -alias MyCertificate -file myCertificate.cer
Enter keystore password: test123456
Certificate stored in file <myCertificate.cer>
now at step4 - i want to sign data.txt use myCertificate.cer. What i must to do. any code or link to artcle which contains code sampleAs I already said, you sign with the private key and not the certificate. You verify with the certificate.
Your first 3 steps are flawed. You need to understand what you are doing so you should do some background reading first.
1) Applied Cryptography, Schneier, Wiley, ISBN 0-471-11709-9
2) Practical Cryptography, Ferguson and Schneier, Wiley, ISBN 0-471-22357-3
3) Java Cryptography, Knudsen, O'Reilly, ISBN 1-56592-402-9 dated but still a good starting point
4) Google
P.S. The basics for signing using Java are given in http://java.sun.com/j2se/1.4.2/docs/guide/security/CryptoSpec.html#Signature