Hi group,
my application should generate signatures(=sign X509 Certificates) with 
a private key which i define with only the values modulus and private 
exponent(no prime factors or other values).Therefore i use the 
RSAPrivateKeySpec Class. In order to generate the signature i pass the 
private key to the sign method of the Class Signature. And thats the 
position my program rises an exception.

java.security.SignatureException: Signing error: 
java.lang.ArithmeticException: BigInteger: modulus not positive
	at iaik.security.rsa.RSASignature.engineSign(Unknown Source)
	at java.security.Signature.sign(Unknown Source)
	at 
robert.distributedCA.DemoApp$MyActionListener.actionPerformed(DemoApp.java:468)
	at java.awt.Button.processActionEvent(Unknown Source)
	at java.awt.Button.processEvent(Unknown Source)
	...

If I pass a generated private Key with all information like the prime 
factors and crt_coefficient, the sign method is working fine.
My explanation for this is that the signature method use additional 
values like the prime factors to compute the signature by using the 
chinese remainder theoreme. Maybe the sign method looks at any of these 
values and throws an exception because of their zero values.
Is this a acceptable explication of my error?
Is it possible to generate X509 Certificate Signatures without using the 
primefactors or crt_coefficient? Maybe i can skip the CRT because as far 
as I know it is just an improvement of speed.

CODE:

PrivateKey privKey = DemoApp.mainApp.getSecurity().getCaPrivateKey();
BigInteger modulus = new BigInteger(1,
         ((RSAPrivateKey)privKey).getModulus().toByteArray());
BigInteger privExponent = new BigInteger(1,
     ((RSAPrivateKey)privKey).getPrivateExponent().toByteArray());
RSAPrivateKeySpec keySpec = new RSAPrivateKeySpec( modulus,
                            privExponent);
KeyFactory kFact = KeyFactory.getInstance("RSA");
privateKey = kFact.generatePrivate(keySpec);

byte[] tbs = cert.getTBSCertificate();
Signature sharsa = Signature.getInstance("SHA1withRSA", "IAIK");
sharsa.initSign(privateKey);
sharsa.update(tbs);
byte[] signatureValue = sharsa.sign();     <- exception

Thanks
Robert

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how I do x509 signature creation