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How to set padding for signed key encryption in java? [duplicate]

I am using rsa key to encrypt a long string which I will send to my server(will encrypt it with server's public key and my private key) But it throws an exception like javax.crypto.IllegalBlockSizeException: Data must not be longer than 256 bytes
I feel that I have not understood the working of rsa properly till now(using the inbuilt libraries are the cause for this). Can some one please explain why this exception is being thrown. Is it not at all possible to send long string encrypted?

The RSA algorithm can only encrypt data that has a maximum byte length
of the RSA key length in bits divided with eight minus eleven padding
bytes, i.e. number of maximum bytes = key length in bits / 8 - 11.
So basicly you divide the key length with 8 -11(if you have padding). For example if you have a 2048bit key you can encrypt 2048/8 = 256 bytes (- 11 bytes if you have padding). So, either use a larger key or you encrypt the data with a symmetric key, and encrypt that key with rsa (which is the recommended approach).
That will require you to:
generate a symmetric key
Encrypt the data with the symmetric key
Encrypt the symmetric key with rsa
send the encrypted key and the data
Decrypt the encrypted symmetric key with rsa
decrypt the data with the symmetric key
done :)

Based on #John Snow answer, I did an example
Generate Symmetric Key (AES with 128 bits)
KeyGenerator generator = KeyGenerator.getInstance("AES");
generator.init(128); // The AES key size in number of bits
SecretKey secKey = generator.generateKey();
Encrypt plain text using AES
String plainText = "Please encrypt me urgently..."
Cipher aesCipher = Cipher.getInstance("AES");
aesCipher.init(Cipher.ENCRYPT_MODE, secKey);
byte[] byteCipherText = aesCipher.doFinal(plainText.getBytes());
Encrypt the key using RSA public key
KeyPairGenerator kpg = KeyPairGenerator.getInstance("RSA");
kpg.initialize(2048);
KeyPair keyPair = kpg.generateKeyPair();
PublicKey puKey = keyPair.getPublic();
PrivateKey prKey = keyPair.getPrivate();
Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
cipher.init(Cipher.PUBLIC_KEY, puKey);
byte[] encryptedKey = cipher.doFinal(secKey.getEncoded()/*Seceret Key From Step 1*/);
Send encrypted data (byteCipherText) + encrypted AES Key (encryptedKey)
On the client side, decrypt symmetric key using RSA private key
cipher.init(Cipher.PRIVATE_KEY, prKey);
byte[] decryptedKey = cipher.doFinal(encryptedKey);
Decrypt the cipher text using decrypted symmetric key
//Convert bytes to AES SecertKey
SecretKey originalKey = new SecretKeySpec(decryptedKey , 0, decryptedKey .length, "AES");
Cipher aesCipher = Cipher.getInstance("AES");
aesCipher.init(Cipher.DECRYPT_MODE, originalKey);
byte[] bytePlainText = aesCipher.doFinal(byteCipherText);
String plainText = new String(bytePlainText);`

You should not use RSA on your secret data directly. You should only ever use RSA on pseudo-random or completely random data, such as session keys or message authentication codes.
You've gotten the problem at 256 bytes -- that is because you're probably working with 2048 bit keys. The keys are able to encrypt any integer in the range 0 to 2^2048 - 1 into the same range, and that means your data must be 256 bytes or smaller.
If you intend to encrypt more than this, please use one RSA encryption to encrypt a session key for a symmetric algorithm, and use that to encrypt your data.

To follow on from John Snow's answer above I created a simple random-symmetric-crypt library that you can use to simply encrypt any length data using a private key.
You can find the library at GitHub - random-symmetric-crypto
final RandomSymmetricCipher cipher = new RandomSymmetricCipher();
// Encrypt the data and the random symmetric key.
final CryptoPacket cryptoPacket = cipher.encrypt(inputData, PRIVATE_KEY_BASE64);
// Convert the CryptoPacket into a Base64 String that can be readily reconstituted at the other end.
final CryptoPacketConverter cryptoPacketConverter = new CryptoPacketConverter();
final String base64EncryptedData = cryptoPacketConverter.convert(cryptoPacket);
System.out.println("Base64EncryptedData=" + base64EncryptedData);
// Decrypt the Base64 encoded (and encrypted) String.
final byte[] outputData = cipher.decrypt(base64EncryptedData, PUBLIC_KEY_BASE64);

I went through the same problem, this is how I solved it.
AES can encrypt data as a standalone algorithm and can also do it with the help of RSA algorithm. Using AES standalone algorithm combined with RSA algorithm in the same block code(function) will cause increase in Data size affecting the AES key Size. You shouldn't do as shown with the code:
//encryption without using RSA KEY both can't run at the same time.
byte[] bytes = Files.readAllBytes(Paths.get(pvtKeyFile));
ks = new PKCS8EncodedKeySpec(bytes);
kf = KeyFactory.getInstance("RSA");
pvt = kf.generatePrivate(ks);
cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
cipher.init(Cipher.ENCRYPT_MODE, pvt);
processFiles(cipher, localFile, localFile + ".enc");
System.out.println("The encrypted files have been created successfully.");
//encryption using RSA.
byte[] bytes = Files.readAllBytes(Paths.get(pvtKeyFile));
ks = new PKCS8EncodedKeySpec(bytes);
kf = KeyFactory.getInstance("RSA");
pvt = kf.generatePrivate(ks);
kgen = KeyGenerator.getInstance("AES");
kgen.init(128);
skey = kgen.generateKey();
byte[] iv = new byte[128/8];
srandom.nextBytes(iv);
ivspec = new IvParameterSpec(iv);
try (FileOutputStream out = new FileOutputStream(localFile + ".enc")) {
{
cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
cipher.init(Cipher.ENCRYPT_MODE, pvt);
byte[] b = cipher.doFinal(skey.getEncoded());
out.write(b);
System.err.println("AES Key Length: " + b.length);
}
out.write(iv);
System.err.println("IV Length: " + iv.length);
ciphers = Cipher.getInstance("AES/CBC/PKCS5Padding");
ciphers.init(Cipher.ENCRYPT_MODE, skey, ivspec);
System.out.println("The encrypted files have been created successfully.");
try (FileInputStream in = new FileInputStream(localFile)) {
processFile(ciphers, in, out);
}
}
You can't do as shown above, it will cause error during the decryption process. if you are to use AES standalone algorithm use it in one block of code without including the RSA algorithm and the vice versa is true, as show below.
//encryption without using RSA KEY both can't run at the same time.
byte[] bytes = Files.readAllBytes(Paths.get(pvtKeyFile));
ks = new PKCS8EncodedKeySpec(bytes);
kf = KeyFactory.getInstance("RSA");
pvt = kf.generatePrivate(ks);
cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
cipher.init(Cipher.ENCRYPT_MODE, pvt);
processFiles(cipher, localFile, localFile + ".enc");
System.out.println("The encrypted files have been created successfully.");
OR
You can only use the RSA Algorithm as shown:
byte[] bytes = Files.readAllBytes(Paths.get(pvtKeyFile));
ks = new PKCS8EncodedKeySpec(bytes);
kf = KeyFactory.getInstance("RSA");
pvt = kf.generatePrivate(ks);
kgen = KeyGenerator.getInstance("AES");
kgen.init(128);
skey = kgen.generateKey();
byte[] iv = new byte[128/8];
srandom.nextBytes(iv);
ivspec = new IvParameterSpec(iv);
try (FileOutputStream out = new FileOutputStream(localFile + ".enc")) {
{
cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
cipher.init(Cipher.ENCRYPT_MODE, pvt);
byte[] b = cipher.doFinal(skey.getEncoded());
out.write(b);
System.err.println("AES Key Length: " + b.length);
}
out.write(iv);
System.err.println("IV Length: " + iv.length);
ciphers = Cipher.getInstance("AES/CBC/PKCS5Padding");
ciphers.init(Cipher.ENCRYPT_MODE, skey, ivspec);
System.out.println("The encrypted files have been created successfully.");
try (FileInputStream in = new FileInputStream(localFile)) {
processFile(ciphers, in, out);
}
}
Thanks I hope it will help someone regards.

you need split your data by the publicKey
int keyLength = publicKey.getModulus().bitLength() / 16;
String[] datas = splitString(data, keyLength - 11);
String mi = ""//the data after encrypted;
for (String s : datas) {
mi += bcd2Str(cipher.doFinal(s.getBytes()));
}
return mi;
public static String bcd2Str(byte[] bytes) {
char temp[] = new char[bytes.length * 2], val;
for (int i = 0; i < bytes.length; i++) {
val = (char) (((bytes[i] & 0xf0) >> 4) & 0x0f);
temp[i * 2] = (char) (val > 9 ? val + 'A' - 10 : val + '0');
val = (char) (bytes[i] & 0x0f);
temp[i * 2 + 1] = (char) (val > 9 ? val + 'A' - 10 : val + '0');
}
return new String(temp);
}

iOS CryptoKit in Java

I am looking for settings/parameters of CryptoKit which will allow me to share data between iOS App and a Java Application. The flow would be something like below:
- Use CryptoKit to encrypt a text using a fixed key and random initialization vector (IV).
- In the Java application use standard javax libraries to perform the decryption using the same fixed key. The random IV will be transported/shared with the application along with the encrypted text.
Similarly, the reverse is also required, where text is encrypted using JavaX libraries using a fixed key and random IV. The random IV and encrypted text is shared with the iOS app where it should use CryptoKit to decrypt it.
Below is the code for Encrypt and Decrypt in Java
public static byte[] encrypt(byte[] plaintext, byte[] key, byte[] IV) throws Exception
{
// Get Cipher Instance
Cipher cipher = Cipher.getInstance("AES_256/GCM/NoPadding");
// Create SecretKeySpec
SecretKeySpec keySpec = new SecretKeySpec(key, "AES");
// Create GCMParameterSpec
GCMParameterSpec gcmParameterSpec = new GCMParameterSpec(GCM_TAG_LENGTH * 8, IV);
// Initialize Cipher for ENCRYPT_MODE
cipher.init(Cipher.ENCRYPT_MODE, keySpec, gcmParameterSpec);
// Perform Encryption
byte[] cipherText = cipher.doFinal(plaintext);
return cipherText;
}
public static String decrypt(byte[] cipherText, byte[] key, byte[] IV) throws Exception
{
// Get Cipher Instance
Cipher cipher = Cipher.getInstance("AES_256/GCM/NoPadding");
// Create SecretKeySpec
SecretKeySpec keySpec = new SecretKeySpec(key, "AES");
// Create GCMParameterSpec
GCMParameterSpec gcmParameterSpec = new GCMParameterSpec(GCM_TAG_LENGTH * 8, IV);
// Initialize Cipher for DECRYPT_MODE
cipher.init(Cipher.DECRYPT_MODE, keySpec, gcmParameterSpec);
// Perform Decryption
byte[] decryptedText = cipher.doFinal(cipherText);
return new String(decryptedText);
}
The CryptoKit commands as below:
let mykey = SymmetricKey(data: passhash)
let myiv = try AES.GCM.Nonce()
let mySealedBox = try AES.GCM.seal(source.data(using: .utf8)!, using: mykey, nonce: myiv)
let myNewSealedBox = try AES.GCM.SealedBox(nonce: myiv, ciphertext: mySealedBox.ciphertext, tag: mySealedBox.tag)
let myText = try String(decoding: AES.GCM.open(myNewSealedBox, using: mykey), as: UTF8.self)
Below are the steps to generate an encrypted text in Java:
int GCM_IV_LENGTH = 12;
//Generate Key
MessageDigest md = MessageDigest.getInstance("SHA265");
byte[] key = md.digest("pass".getBytes(StandardCharsets.UTF_8));
// Generate IV
SecureRandom sr = new SecureRandom(pass.getBytes(StandardCharsets.UTF_8));
byte[] IV = new byte[GCM_IV_LENGTH];
sr.nextBytes(IV);
//Encrypt
byte[] cipherText = encrypt("Text to encrypt".getBytes(), key, IV);
//Base64 Encoded CipherText
String cipherTextBase64 = Base64.getEncoder().encodeToString(cipherText);
To Decrypt this in SWIFT CryptoKit, I first need to create a sealed box with this CipherText however, the CryptoKit API to create a sealed box requires the following:
Nonce/IV (Available above)
CipherText (Available above)
Tag (NO IDEA FROM WHERE TO GET THIS????)
AES.GCM.SealedBox(nonce: , ciphertext: , tag: )
The other way, lets first encrypt data in CryptoKit
let mykey = SymmetricKey(data: SHA256.hash(data: "12345".data(using: .utf8)!))
let myiv = AES.GCM.Nonce()
let mySealedBox = try AES.GCM.seal("Text to encrypt".data(using: .utf8)!, using: mykey, nonce: myiv)
let cipherText = mySealedBox.cipherText.base64EncodedString()
let iv = myiv.withUnsafeBytes{
return Data(Array($0)).base64EncodedString()
}
If i pass this IV and CipherText to Java Decrypt function along with key (SHA265 hash of "12345" string), i get a TAG mismatch error.

This is the final set of code in SWIFT:
let pass = “Password”
let data = “Text to encrypt”.data(using: .utf8)!
let key = SymmetricKey(data: SHA256.hash(data: pass.datat(using: .utf8)!))
let iv = AES.GCM.Nonce()
let mySealedBox = try AES.GCM.seal(data, using: key, nonce: iv)
dataToShare = mySealedBox.combined?.base64EncodedData()
Write this data to a file (I am using google APIs to write this data to a file on google drive)
Read this data from the file in java and pass it to the functions as defined in the question using the below code:
byte[] iv = Base64.getDecoder().decode(text.substring(0,16));
cipher[] = Base64.getDecoder().decode(text.substring(16));
byte[] key = md.digest(pass.getBytes(StandardCharsets.UTF_8));
String plainText = decrypt(cipher, key, iv);

How to properly recreate SecretKey from string

I'm trying to make an encryption-decryption app. I've got two classes - one with functions to generate the key, encrypt and decrypt, second one for JavaFX GUI. In the GUI class I've got 4 textareas: 1st to write text to encrypt, 2nd for encrypted text, 3rd for the key (String encodedKey = Base64.getEncoder().encodeToString(klucz.getEncoded());) and 4th for decrypted text.
The problem is, I am not able to decrypt the text. I'm trying to recreate the SecretKey like this:
String encodedKey = textAreaKey.getText();
byte[] decodedKey = Base64.getDecoder().decode(encodedKey);
SecretKey klucz = new SecretKeySpec(decodedKey, "DESede");
When I encrypt the key looks like this: com.sun.crypto.provider.DESedeKey#4f964d80 and when I try to recreate it: javax.crypto.spec.SecretKeySpec#4f964d80 and I'm getting javax.crypto.IllegalBlockSizeException: Input length must be multiple of 8 when decrypting with padded cipher
Here is my 1st class:
public class Encryption {
public static SecretKey generateKey() throws NoSuchAlgorithmException {
Security.addProvider(new com.sun.crypto.provider.SunJCE());
KeyGenerator keygen = KeyGenerator.getInstance("DESede");
keygen.init(168);
SecretKey klucz = keygen.generateKey();
return klucz;
}
static byte[] encrypt(byte[] plainTextByte, SecretKey klucz)
throws Exception {
Cipher cipher = Cipher.getInstance("DESede/ECB/PKCS5Padding");
cipher.init(Cipher.ENCRYPT_MODE, klucz);
byte[] encryptedBytes = cipher.doFinal(plainTextByte);
return encryptedBytes;
}
static byte[] decrypt(byte[] encryptedBytes, SecretKey klucz)
throws Exception {
Cipher cipher = Cipher.getInstance("DESede/ECB/PKCS5Padding");
cipher.init(Cipher.DECRYPT_MODE, klucz);
byte[] decryptedBytes = cipher.doFinal(encryptedBytes);
return decryptedBytes;
}
}
edit
btnEncrypt.setOnAction((ActionEvent event) -> {
try {
String plainText = textAreaToEncrypt.getText();
SecretKey klucz = Encryption.generateKey();
byte[] plainTextByte = plainText.getBytes();
byte[] encryptedBytes = Encryption.encrypt(plainTextByte, klucz);
String encryptedText = Base64.getEncoder().encodeToString(encryptedBytes);
textAreaEncryptedText.setText(encryptedText);
byte[] byteKey = klucz.getEncoded();
String stringKey = Base64.getEncoder().encodeToString(byteKey);
textAreaKey.setTextstringKey
} catch (Exception ex) {
ex.printStackTrace();
}
});
btnDecrypt.setOnAction((ActionEvent event) -> {
try {
String stringKey = textAreaKey.getText();
byte[] decodedKey = Base64.getDecoder().decode(encodedKey);
SecretKey klucz2 = new SecretKeySpec(decodedKey, "DESede");
String encryptedText = textAreaEncryptedText.getText();
byte[] encryptedBytes = Base64.getDecoder().decode(encryptedText.getBytes());
byte[] decryptedBytes = Encryption.decrypt(encryptedBytes, klucz2;
String decryptedText = Base64.getEncoder().encodeToString(decryptedBytes);
textAreaDecryptedText.setText(decryptedText);
} catch (Exception ex) {
ex.printStackTrace();
}
});

One of your problems is here:
String encryptedText = new String(encryptedBytes, "UTF8");
Generally, many byte sequences in cipher text are not valid UTF-8–encoded characters. When you try to create a String, this malformed sequences will be replaced with the "replacement character", and then information from the the cipher text is irretrievably lost. When you convert the String back to bytes and try to decrypt it, the corrupt cipher text raises an error.
If you need to represent the cipher text as a character string, use base-64 encoding, just as you do for the key.
The other principal problem is that you are aren't specifying the full transformation. You should specify the "mode" and "padding" of the cipher explicitly, like "DESede/ECB/PKCS5Padding".
The correct mode will depend on your assignment. ECB is generally not secure, but more secure modes add a bit of complexity that may be outside the scope of your assignment. Study your instructions and clarify the requirements with your teacher if necessary.

There are two main issues:
You should not use user entered password as a key (there are difference between them). The key must have specific size depending on the cipher (16 or 24 bytes for 3des)
Direct 3DES (DESede) is a block cipher encrypting 8 bytes at once. To encrypt multiple blocks, there are some methods defined how to do that properly. It is calls Block cipher mode.
For proper encryption you need to take care of a few more things
Creating a key from the password
Let's assume you want to use DESede (3des). The key must have fixed size - 16 or 24 bytes. To properly generate a key from password you should use PBKDF. Some people are sensitive to "must use", however neglecting this step really compromises the encryption security mainly using user-entered passwords.
For 3DES you can use :
int keySize = 16*8;
int iterations = 800000;
char[] password = "password".toCharArray();
SecureRandom random = new SecureRandom();
byte[] salt = random.generateSeed(8);
SecretKeyFactory secKeyFactory = SecretKeyFactory.getInstance("PBKDF2WithHmacSHA512");
KeySpec spec = new PBEKeySpec(password, salt, iterations, keySize);
SecretKey pbeSecretKey = secKeyFactory.generateSecret(spec);
SecretKey desSecret = new SecretKeySpec(pbeSecretKey.getEncoded(), "DESede");
// iv needs to have block size
// we will use the salt for simplification
IvParameterSpec ivParam = new IvParameterSpec(salt);
Cipher cipher = Cipher.getInstance("DESEde/CBC/PKCS5Padding");
cipher.init(Cipher.ENCRYPT_MODE, desSecret, ivParam);
System.out.println("salt: "+Base64.getEncoder().encodeToString(salt));
System.out.println(cipher.getIV().length+" iv: "+Base64.getEncoder().encodeToString(cipher.getIV()));
byte[] ciphertext = cipher.doFinal("plaintext input".getBytes());
System.out.println("encrypted: "+Base64.getEncoder().encodeToString(ciphertext));
if you can ensure that your password has good entropy (is long and random enough) you may be good with a simple hash
MessageDigest dgst = MessageDigest.getInstance("sha-1");
byte[] hash = dgst.digest("some long, complex and random password".getBytes());
byte[] keyBytes = new byte[keySize/8];
System.arraycopy(hash, 0, keyBytes, 0, keySize/8);
SecretKey desSecret = new SecretKeySpec(keyBytes, "DESede");
The salt serves to randomize the output and should be used.
The output of the encryption should be salt | cipthertext | tag (not necessarily in this order, but you will need all of these for proper encryption).
To decrypt the output, you will need to split the output to salt, ciphertext and the tag.
I see zero vectors ( static salt or iv ) very often in examples from StackOverflow, but in many cases it may lead to broken ciphers revelaling key or plaintext.
The initialization vector iv is needed for block chain modes (encrypting longer input than a single block), we could use the salt from the key as well
when having the same size ( 8 bytes in our case). For really secure solution the password salt should be longer.
The tag is an authentication tag, to ensure that nobody has manipulated with the ciphertext. You could use HMAC of the plaintext or ciphertext. It is important you should use different key for HMAC than for encryption. However - I believe in your case your homework will be ok even without the hmac tag

getting a IllegalBlockSizeException: Data must not be longer than 256 bytes when using rsa

I am using rsa key to encrypt a long string which I will send to my server(will encrypt it with server's public key and my private key) But it throws an exception like javax.crypto.IllegalBlockSizeException: Data must not be longer than 256 bytes
I feel that I have not understood the working of rsa properly till now(using the inbuilt libraries are the cause for this). Can some one please explain why this exception is being thrown. Is it not at all possible to send long string encrypted?

The RSA algorithm can only encrypt data that has a maximum byte length
of the RSA key length in bits divided with eight minus eleven padding
bytes, i.e. number of maximum bytes = key length in bits / 8 - 11.
So basicly you divide the key length with 8 -11(if you have padding). For example if you have a 2048bit key you can encrypt 2048/8 = 256 bytes (- 11 bytes if you have padding). So, either use a larger key or you encrypt the data with a symmetric key, and encrypt that key with rsa (which is the recommended approach).
That will require you to:
generate a symmetric key
Encrypt the data with the symmetric key
Encrypt the symmetric key with rsa
send the encrypted key and the data
Decrypt the encrypted symmetric key with rsa
decrypt the data with the symmetric key
done :)

Based on #John Snow answer, I did an example
Generate Symmetric Key (AES with 128 bits)
KeyGenerator generator = KeyGenerator.getInstance("AES");
generator.init(128); // The AES key size in number of bits
SecretKey secKey = generator.generateKey();
Encrypt plain text using AES
String plainText = "Please encrypt me urgently..."
Cipher aesCipher = Cipher.getInstance("AES");
aesCipher.init(Cipher.ENCRYPT_MODE, secKey);
byte[] byteCipherText = aesCipher.doFinal(plainText.getBytes());
Encrypt the key using RSA public key
KeyPairGenerator kpg = KeyPairGenerator.getInstance("RSA");
kpg.initialize(2048);
KeyPair keyPair = kpg.generateKeyPair();
PublicKey puKey = keyPair.getPublic();
PrivateKey prKey = keyPair.getPrivate();
Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
cipher.init(Cipher.PUBLIC_KEY, puKey);
byte[] encryptedKey = cipher.doFinal(secKey.getEncoded()/*Seceret Key From Step 1*/);
Send encrypted data (byteCipherText) + encrypted AES Key (encryptedKey)
On the client side, decrypt symmetric key using RSA private key
cipher.init(Cipher.PRIVATE_KEY, prKey);
byte[] decryptedKey = cipher.doFinal(encryptedKey);
Decrypt the cipher text using decrypted symmetric key
//Convert bytes to AES SecertKey
SecretKey originalKey = new SecretKeySpec(decryptedKey , 0, decryptedKey .length, "AES");
Cipher aesCipher = Cipher.getInstance("AES");
aesCipher.init(Cipher.DECRYPT_MODE, originalKey);
byte[] bytePlainText = aesCipher.doFinal(byteCipherText);
String plainText = new String(bytePlainText);`

You should not use RSA on your secret data directly. You should only ever use RSA on pseudo-random or completely random data, such as session keys or message authentication codes.
You've gotten the problem at 256 bytes -- that is because you're probably working with 2048 bit keys. The keys are able to encrypt any integer in the range 0 to 2^2048 - 1 into the same range, and that means your data must be 256 bytes or smaller.
If you intend to encrypt more than this, please use one RSA encryption to encrypt a session key for a symmetric algorithm, and use that to encrypt your data.

To follow on from John Snow's answer above I created a simple random-symmetric-crypt library that you can use to simply encrypt any length data using a private key.
You can find the library at GitHub - random-symmetric-crypto
final RandomSymmetricCipher cipher = new RandomSymmetricCipher();
// Encrypt the data and the random symmetric key.
final CryptoPacket cryptoPacket = cipher.encrypt(inputData, PRIVATE_KEY_BASE64);
// Convert the CryptoPacket into a Base64 String that can be readily reconstituted at the other end.
final CryptoPacketConverter cryptoPacketConverter = new CryptoPacketConverter();
final String base64EncryptedData = cryptoPacketConverter.convert(cryptoPacket);
System.out.println("Base64EncryptedData=" + base64EncryptedData);
// Decrypt the Base64 encoded (and encrypted) String.
final byte[] outputData = cipher.decrypt(base64EncryptedData, PUBLIC_KEY_BASE64);

I went through the same problem, this is how I solved it.
AES can encrypt data as a standalone algorithm and can also do it with the help of RSA algorithm. Using AES standalone algorithm combined with RSA algorithm in the same block code(function) will cause increase in Data size affecting the AES key Size. You shouldn't do as shown with the code:
//encryption without using RSA KEY both can't run at the same time.
byte[] bytes = Files.readAllBytes(Paths.get(pvtKeyFile));
ks = new PKCS8EncodedKeySpec(bytes);
kf = KeyFactory.getInstance("RSA");
pvt = kf.generatePrivate(ks);
cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
cipher.init(Cipher.ENCRYPT_MODE, pvt);
processFiles(cipher, localFile, localFile + ".enc");
System.out.println("The encrypted files have been created successfully.");
//encryption using RSA.
byte[] bytes = Files.readAllBytes(Paths.get(pvtKeyFile));
ks = new PKCS8EncodedKeySpec(bytes);
kf = KeyFactory.getInstance("RSA");
pvt = kf.generatePrivate(ks);
kgen = KeyGenerator.getInstance("AES");
kgen.init(128);
skey = kgen.generateKey();
byte[] iv = new byte[128/8];
srandom.nextBytes(iv);
ivspec = new IvParameterSpec(iv);
try (FileOutputStream out = new FileOutputStream(localFile + ".enc")) {
{
cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
cipher.init(Cipher.ENCRYPT_MODE, pvt);
byte[] b = cipher.doFinal(skey.getEncoded());
out.write(b);
System.err.println("AES Key Length: " + b.length);
}
out.write(iv);
System.err.println("IV Length: " + iv.length);
ciphers = Cipher.getInstance("AES/CBC/PKCS5Padding");
ciphers.init(Cipher.ENCRYPT_MODE, skey, ivspec);
System.out.println("The encrypted files have been created successfully.");
try (FileInputStream in = new FileInputStream(localFile)) {
processFile(ciphers, in, out);
}
}
You can't do as shown above, it will cause error during the decryption process. if you are to use AES standalone algorithm use it in one block of code without including the RSA algorithm and the vice versa is true, as show below.
//encryption without using RSA KEY both can't run at the same time.
byte[] bytes = Files.readAllBytes(Paths.get(pvtKeyFile));
ks = new PKCS8EncodedKeySpec(bytes);
kf = KeyFactory.getInstance("RSA");
pvt = kf.generatePrivate(ks);
cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
cipher.init(Cipher.ENCRYPT_MODE, pvt);
processFiles(cipher, localFile, localFile + ".enc");
System.out.println("The encrypted files have been created successfully.");
OR
You can only use the RSA Algorithm as shown:
byte[] bytes = Files.readAllBytes(Paths.get(pvtKeyFile));
ks = new PKCS8EncodedKeySpec(bytes);
kf = KeyFactory.getInstance("RSA");
pvt = kf.generatePrivate(ks);
kgen = KeyGenerator.getInstance("AES");
kgen.init(128);
skey = kgen.generateKey();
byte[] iv = new byte[128/8];
srandom.nextBytes(iv);
ivspec = new IvParameterSpec(iv);
try (FileOutputStream out = new FileOutputStream(localFile + ".enc")) {
{
cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
cipher.init(Cipher.ENCRYPT_MODE, pvt);
byte[] b = cipher.doFinal(skey.getEncoded());
out.write(b);
System.err.println("AES Key Length: " + b.length);
}
out.write(iv);
System.err.println("IV Length: " + iv.length);
ciphers = Cipher.getInstance("AES/CBC/PKCS5Padding");
ciphers.init(Cipher.ENCRYPT_MODE, skey, ivspec);
System.out.println("The encrypted files have been created successfully.");
try (FileInputStream in = new FileInputStream(localFile)) {
processFile(ciphers, in, out);
}
}
Thanks I hope it will help someone regards.

you need split your data by the publicKey
int keyLength = publicKey.getModulus().bitLength() / 16;
String[] datas = splitString(data, keyLength - 11);
String mi = ""//the data after encrypted;
for (String s : datas) {
mi += bcd2Str(cipher.doFinal(s.getBytes()));
}
return mi;
public static String bcd2Str(byte[] bytes) {
char temp[] = new char[bytes.length * 2], val;
for (int i = 0; i < bytes.length; i++) {
val = (char) (((bytes[i] & 0xf0) >> 4) & 0x0f);
temp[i * 2] = (char) (val > 9 ? val + 'A' - 10 : val + '0');
val = (char) (bytes[i] & 0x0f);
temp[i * 2 + 1] = (char) (val > 9 ? val + 'A' - 10 : val + '0');
}
return new String(temp);
}

Decrypt AES encrypted file in java

I have a file encrypted with java application using AES. I also have a key file was encrypted with. But i can't understand how to use the key to decrypt file. Most tutorials and examples create temporary random key, encrypt file and decrypt it in one place.
So, question is how to specify a key which have to be used for decryption?
EDIT:
Samples i found use following code to generate key. I have no idea where i can use my key here.
KeyGenerator kgen = KeyGenerator.getInstance("AES");
kgen.init(128);
SecretKey key = kgen.generateKey();

Just to summarise my comments to Lucifer's answer.
If you don't know what padding was used to encrypt, then decrypt with 'no padding' set. That will decrypt everything, including the padding, and won't throw an error because of mismatched padding.
When you have decrypted the cyphertext, have a look at the last block of the output and see what padding was used. Different paddings leave different byte patterns, so it is usually easy enough to tell.
Set your decryption method to expect the correct type of padding, and it will be automatically removed for you.

The answer could be simply to put the key data as bytes into a SecretKeySpec like this:
SecretKeySpec aesKey = new SecretKeySpec(myKeyData, "AES");
Note that SecretKeySpec implements the Key interface, so you can use it directly in a Cipher.init() method. So there is no SecretKeyFactory needed, which you would use otherwise.

Please try following methods, if might helpful for you.
private static byte[] cipherData(PaddedBufferedBlockCipher cipher, byte[] data)
throws Exception
{
int minSize = cipher.getOutputSize(data.length);
byte[] outBuf = new byte[minSize];
int length1 = cipher.processBytes(data, 0, data.length, outBuf, 0);
int length2 = cipher.doFinal(outBuf, length1);
int actualLength = length1 + length2;
byte[] result = new byte[actualLength];
System.arraycopy(outBuf, 0, result, 0, result.length);
return result;
}
private static byte[] decrypt(byte[] cipher, byte[] key, byte[] iv) throws Exception
{
PaddedBufferedBlockCipher aes = new PaddedBufferedBlockCipher(new CBCBlockCipher(
new AESEngine()));
CipherParameters ivAndKey = new ParametersWithIV(new KeyParameter(key), iv);
aes.init(false, ivAndKey);
return cipherData(aes, cipher);
}
private static byte[] encrypt(byte[] plain, byte[] key, byte[] iv) throws Exception
{
PaddedBufferedBlockCipher aes = new PaddedBufferedBlockCipher(new CBCBlockCipher(
new AESEngine()));
CipherParameters ivAndKey = new ParametersWithIV(new KeyParameter(key), iv);
aes.init(true, ivAndKey);
return cipherData(aes, plain);
}

Complete example of encrypting/Decrypting a huge video without throwing Java OutOfMemoryException and using Java SecureRandom for Initialization Vector generation. Also depicted storing key bytes to database and then reconstructing same key from those bytes.
https://stackoverflow.com/a/18892960/185022