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The FromXmlString initializes an RSA object using key information in an XML string that was generated using the ToXmlString method. The FromXmlString method accepts either an XML string containing a public key or an XML string containing a public and private key. Use the FromXmlString method to conveniently initialize RSA key information.
- 3. Saving the Keys in Binary Format
- Source Code
Generate a keypair for encrypting on your dev server. Openssl genrsa -des3 -out private.pem 2048. Openssl rsa -in private.pem -outform PEM -pubout -out public.pem. Store the public key in the application code, doesn't matter where. This will be used in the function at step 5. Maybe obfuscate the code to prevent altering of the encrypting mechanism. I want to use JWT generate policy using RSA256 algorithm. This is for learning purpose, so I'm using assign message policy for 'private.privatekey' which has to be PEM encoded RSA private key. I thought of using a sample base64 encoded strin, but it did'nt worked out. I'm a 500 response. In Windows, use PuTTYgen to generate your public and private keys. If needed, download PuTTYgen from the PuTTY download page. (PuTTYgen might have been installed previously with PuTTY or WinSCP.) Launch the program, and then click the Generate button. Keys that begin with '-BEGIN RSA PRIVATE KEY' are pkcs1 encoded files. This pkcs1 encoding is not supported by Java unless you an external library like BouncyCastle. I ran into the same issue yesterday and after about 8 hours, found the solution.
1. Introduction
Let us learn the basics of generating and using RSA keys in Java.
Java provides classes for the generation of RSA public and private key pairs with the package java.security. You can use RSA keys pairs in public key cryptography.
Public key cryptography uses a pair of keys for encryption. Distribute the public key to whoever needs it but safely secure the private key.
Public key cryptography can be used in two modes:
Encryption: Only the private key can decrypt the data encrypted with the public key.
Authentication: Data encrypted with the private key can only be decrypted with the public key thus proving who the data came from.
2. Generating a Key Pair
First step in creating an RSA Key Pair is to create a KeyPairGeneratorfrom a factory method by specifying the algorithm (“RSA” in this instance):
Initialize the KeyPairGenerator with the key size. Use a key size of 1024 or 2048. Currently recommended key size for SSL certificates used in e-commerce is 2048 so that is what we use here.
From the KeyPair object, get the public key using getPublic() and the private key using getPrivate().
3. Saving the Keys in Binary Format
Save the keys to hard disk once they are obtained. This allows re-using the keys for encryption, decryption and authentication.
What is the format of the saved files? The key information is encoded in different formats for different types of keys. Here is how you can find what format the key was saved in. On my machine, the private key was saved in PKCS#8 format and the public key in X.509 format. We need this information below to load the keys.
3.1. Load Private Key from File
After saving the private key to a file (or a database), you might need to load it at a later time. You can do that using the following code. Note that you need to know what format the data was saved in: PKCS#8 in our case.
3.2 Load Public Key from File
Load the public key from a file as follows. The public key has been saved in X.509 format so we use the X509EncodedKeySpec class to convert it.
4. Use Base64 for Saving Keys as Text
Save the keys in text format by encoding the data in Base64. Java 8 provides a Base64 class which can be used for the purpose. Save the private key with a comment as follows:
And the public key too (with a comment):
5. Generating a Digital Signature
As mentioned above, one of the purposes of public key cryptography is digital signature i.e. you generate a digital signature from a file contents, sign it with your private key and send the signature along with the file. The recipient can then use your public key to verify that the signature matches the file contents.
Here is how you can do it. Use the signature algorithm “SHA256withRSA” which is guaranteed to be supported on all JVMs. Use the private key (either generated or load from file as shown above) to initialize the Signatureobject for signing. It is then updated with contents from the data file and the signature is generated and written to the output file. This output file contains the digital signature and must be sent to the recipient for verification.
6. Verifying the Digital Signature
The recipient uses the digital signature sent with a data file to verify that the data file has not been tampered with. It requires access to the sender’s public key and can be loaded from a file if necessary as presented above.
The code below updates the Signature object with data from the data file. It then loads the signature from file and uses Signature.verify() to check if the signature is valid.
And that in a nutshell is how you can use RSA public and private keys for digital signature and verification.
Source Code
Go here for the source code.
-->Definition
Creates and returns an XML string containing the key of the current RSA object.
Parameters
Generate Rsa Private Key
- includePrivateParameters
- Boolean
true to include a public and private RSA key; false to include only the public key.
Generate Rsa Private Key From String C
Returns
An XML string containing the key of the current RSA object.
Exceptions
.NET Core only: This member is not supported.
Remarks
The ToXmlString method creates an XML string that contains either the public and private key of the current RSA object or contains only the public key of the current RSA object.
Use the ToXmlString method whenever you need to conveniently persist RSA key information. To initialize an RSA object with the key in an XML string, use the FromXmlString method.
Caution
Persisting an XML string containing a private key to an insecure location is a security threat. The security of your application can be compromised if a malicious third party can access your private key. To safely persist a private key, use a secure key container. For more information about persisting private keys in a key container, see How to: Store Asymmetric Keys in a Key Container.
When you pass true to the ToXmlString method, the resulting XML string takes the following form:
When you pass false to the ToXmlString method, the resulting XML string takes the following form: