Generating RSA keys in PKCS#1 format in Java

Question

When I generate an RSA key pair using the Java API, the public key is encoded in the X.509 format and the private key is encoded in the PKCS#8 format. I\'m looking to encod

Answer 1

I was trying to generate OpenSSL-friendly RSA public keys in DER format using BountyCastle J2ME library ported to BlackBerry, my code:

public void testMe() throws Exception {
  RSAKeyPairGenerator generator = new RSAKeyPairGenerator();
  generator.init(new RSAKeyGenerationParameters(BigInteger.valueOf(0x10001),
                 new SecureRandom(), 512, 80));
  AsymmetricCipherKeyPair keyPair = generator.generateKeyPair();

  RSAKeyParameters params =  (RSAKeyParameters) keyPair.getPublic();
  RSAPublicKeyStructure struct = new RSAPublicKeyStructure(params.getModulus(), 
                                                           params.getExponent());

  SubjectPublicKeyInfo info = 
    new SubjectPublicKeyInfo(new AlgorithmIdentifier("1.2.840.113549.1.1.1"), 
                             struct);

  byte[] bytes = info.getDEREncoded();

  FileOutputStream out = new FileOutputStream("/tmp/test.der");

  out.write(bytes);
  out.flush();
  out.close();
}

Key was still incorrect:

$ openssl asn1parse -in test.der -inform DER -i
0:d=0  hl=2 l=  90 cons: SEQUENCE          
2:d=1  hl=2 l=  11 cons:  SEQUENCE          
4:d=2  hl=2 l=   9 prim:   OBJECT            :rsaEncryption
15:d=1  hl=2 l=  75 prim:  BIT STRING     

I changed org.bouncycastle.asn1.x509.AlgorithmIdentifier

public AlgorithmIdentifier(
    String     objectId)
{
    this.objectId = new DERObjectIdentifier(objectId);
    // This line has been added
    this.parametersDefined = true;
}

And now have nice key:

$ openssl asn1parse -in test.der -inform DER -i
0:d=0  hl=2 l=  92 cons: SEQUENCE          
2:d=1  hl=2 l=  13 cons:  SEQUENCE          
4:d=2  hl=2 l=   9 prim:   OBJECT            :rsaEncryption
15:d=2  hl=2 l=   0 prim:   NULL              
17:d=1  hl=2 l=  75 prim:  BIT STRING 

Which can be used to encrypt:

$ echo "123" | openssl rsautl -pubin  -inkey test.der -encrypt -keyform DER -out y
$ wc -c y
64 y