Generate a Public-Private Key Pair. There are several ways to generate a Public-Private Key Pair depending on your platform. In this example, we will create a pair using Java. The Cryptographic Algorithm we will use in this example is RSA. Generating a Key Pair The Java KeyPairGenerator class (java.security.KeyPairGenerator) is used to generate asymmetric encryption / decryption key pairs. Public Key, Private Key Type Key Pairs The most commonly known type of asymmetric key pair is the public key, private key type of key pair.
Contents
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 https://brownani681.weebly.com/blog/songsheet-generator-code-for-key-change. : Only the private key can decrypt the data encrypted with the public key. Generate ssh key mac command line delete file.
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): https://brownani681.weebly.com/blog/sonic-generations-steam-key-free.
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.
“The secret of education lies in respecting the pupil.”
― Ralph Waldo Emerson
Contents
1. Introduction
In the previous part of this article, we covered the use of RSA for file encryption and decryption in java. Using RSA directly for file encryption will not work since it can only be used with small buffer sizes. In our particular case, with an RSA key size of 2048 bits, we ran into a limitation of a maximum of 245 bytes for the data size.
The solution for this limitation is to use a symmetric algorithm such as AES for encryption while using RSA for encrypting the AES secret key itself. When using AES for encryption, the initialization vector (IV) also needs to be communicated to the receiver for being able to decrypt the message. The entire process of using AES for encryption is covered in detail in this article here.
In the current case, we will generate an AES key, use the AES key for encrypting the file, and use RSA for encrypting the AES key. The output file is generated by including the encrypted AES key at the beginning of the file, followed by the initialization vector (IV) and finally the file data encrypted by AES. This way, just the output file can be delivered to the receiver, instead of the three separate components.
[Note: Check out how to use AES for file encryption and decryption in python.]
2. Java Imports
These are the required java imports for the implementation
3. Generating the AES Key
First step is to generate the AES key which will be used for the encryption. We generate a key of size 128 bits.
Java Generate Private Key Rsa Download
Where key will be generated. We also need the initialization vector of the same size as the key, which we generate as follows (along with the required IvParameterSpec):
4. Loading the RSA Private Key
Load the RSA private key from file using the appropriate class.
5. Save the AES Key
As mentioned above, the first part of the output file contains the encrypted AES key. For encryption, we use the Cipher class with the RSA private key and save it as follows:
6. Write the Initialization Vector
The initialization vector is next written to the output file. This is required for decryption using the AES key.
7. Encrypting the File Contents using the AES Key
The final step is to encrypt the contents of the file using the AES and write it to the output file.
Close the output file and send it to the receiver.
8. Decrypting the File using the RSA Public Key
Since the private key has been used for encryption, the public key can be used for decrypting the file contents. Remember that the file includes the AES key encrypted with the RSA private key at the beginning followed by the initialization vector, and the encrypted file data itself. So the decryption process has to handle all these steps in order to get at the file data.
9. Load the RSA Public Key from File
We use the following code to load the RSA public key from a file where it has been saved in binary format.
10. Load the AES Secret Key
Open the encrypted file and load the AES secret key. The AES secret key can be obtained from this data by decrypting using the RSA public key.
11. Read the Initialization Vector
Next in the file is the initialization vector. Load it as follows:
12. Decrypt the File Contents
Now comes the actual decryption of the file contents using the AES secret key. The output is written into a file with the extension .ver for verification purposes.
Java Generate Rsa Private Key From String
The static method processFile() is defined as before.
At this point the whole file has been decrypted and saved. You can verify that it matches the original file contents.
Conclusion
File encryption and decryption using RSA is somewhat involved since RSA encryption has a very low limit on the data that can be encrypted. The previous part of the article covered the details. To encrypt larger quantities of data, we need to use a symmetric algorithm such as AES for encryption and RSA for encrypting the AES key itself.
And here is the source code relevant to this blog post.
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