Thursday, January 28, 2016

RSA Assymmetric Key Encryption


In addition to the standard X509 *.cer certificates there are also certificate files ending with *.PFX or *.P12.The later ones are X509 certs as well, but may in addition contain a private key, too. PFX was a Microsoft extension, while P12 was the Netscape one.

Generating from Scratch using OpenSSL


1. Generate a 2048-bit RSA private key
$ openssl genrsa -out private_key.pem 2048
This will generate a key file in traditional key format also called ssLeay private key format.
2. Convert private Key to PKCS#8 format (so Java can read it)
$ openssl pkcs8 -topk8 -inform PEM -outform DER -in private_key.pem -out private_key.der -nocrypt
3. Output public key portion in DER format (so Java can read it)
$ openssl rsa -in private_key.pem -pubout -outform DER -out public_key.der



Generating from the .p12 File


  • Private key:
    openssl pkcs12 -in yourP12File.pfx -nocerts -out privateKey.pem
    This will generate the private key alone 
  • Certificates:
    openssl pkcs12 -in yourP12File.pfx -clcerts -nokeys -out publicCert.pem
    this will generate the certificate and private key in one .pem file. 
After this use the Steps 2 and 3 above to generate the certificate files.



Sample Code to Test


public class TestAssymmetric {

public static void main(String[] args) throws InvalidKeySpecException, NoSuchAlgorithmException, IOException, InvalidKeyException, NoSuchPaddingException, InvalidAlgorithmParameterException, IllegalBlockSizeException, BadPaddingException
{
AssymmetricEncryptor encypter=new AssymmetricEncryptor();
PublicKey publicKey = encypter.getPublicKey("C:\\Users\\apillai\\Documents\\Assets\\public_key.der");
System.out.println(publicKey);

String clearText = "hello world";
System.out.println("Clear Text:" + clearText);
String encryptedString = encypter.encrypt(clearText,publicKey);
System.out.println("Encrypted String:" + encryptedString);
System.out.println("Encrypted String: Encoded" + Base64.encode(encryptedString.getBytes()));

PrivateKey privateKey = encypter.getPrivateKey("C:\\Users\\apillai\\Documents\\Assets\\private_key.der");
System.out.println(privateKey);
String decryptedString = encypter.decrypt(encryptedString,privateKey);
System.out.println(decryptedString);
}

}

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