I had a project in which (RSA) encryption was necessary, this is how I reconstructed the publicKey given the publicKey's byte array, that was just read from the file.
public PublicKey reconstruct_public_key(String algorithm, byte[] pub_key) {
PublicKey public_key = null;
try {
KeyFactory kf = KeyFactory.getInstance(algorithm);
EncodedKeySpec pub_key_spec = new X509EncodedKeySpec(pub_key);
public_key = kf.generatePublic(pub_key_spec);
} catch(NoSuchAlgorithmException e) {
System.out.println("Could not reconstruct the public key, the given algorithm oculd not be found.");
} catch(InvalidKeySpecException e) {
System.out.println("Could not reconstruct the public key");
}
return public_key;
}
Then you could call the procedure similar to this call, reconstruct_public_key("RSA", readFileBytes("path/to/your/publicKey/file"));
EDIT : I tried to do it myself (write the public key to a file, read that file and reconstruct the key). This works :
public static void main(String args[]) {
String path = "./pub_key_test.txt";
// Generate a keypair to write to file
KeyPair kp = generate_key();
PublicKey pub_key = kp.getPublic();
File file = new File(path);
try {
// Write to file
file.createNewFile();
FileOutputStream out = new FileOutputStream(path);
out.write(pub_key.getEncoded()); // Write public key to the file
out.close();
// Read from file
FileInputStream in = new FileInputStream(path);
byte[] pub_key_arr = new byte[in.available()];
in.read(pub_key_arr, 0, in.available());
in.close();
// Reconstruct public key
PublicKey reconstructed_pub_key = reconstruct_public_key("RSA", pub_key_arr);
} catch(IOException e) {
System.out.println("Could not open the file : " + e.getStackTrace());
}
}
And this is the generate_key procedure :
public KeyPair generate_key() {
while(true) { // Else the compiler will complain that this procedure does not always return a "KeyPair"
try {
final KeyPairGenerator key_generator = KeyPairGenerator.getInstance("RSA");
key_generator.initialize(2048); // Keys of 2048 bits (minimum key length for RSA keys) are safe enough (according to the slides 128bit keys > 16 years to brute force it)
final KeyPair keys = key_generator.generateKeyPair();
return keys;
} catch(NoSuchAlgorithmException e) {
System.out.println("The given encryption algorithm (RSA) does not exist. -- generate_key() - Cryptography.");
}
}
}
If you test this, you will see that the publicKey is reconstructed successfully.
EDIT : I tried doing it myself, using the ssh-keygen tool. This is what i did :
- First I generated a RSA private key (
.PEM format)
- Outputted the public key portion to
.DER format, so it can be used by Java.
This is how I did the conversion, which is a bit different of yours :
openssl rsa -in private_key_file.pem -pubout -outform DER -out java_readable_file.der
And I did the file reading like here, which doesn't differ much of yours. I tested this and Java successfully reconstructed the public key.
