Using RSA encryption in Java without BouncyCastle

Question

In my program, I'm trying to encrypt some plaintext with RSA using the following code: ``` static String RSAEncrypt(String pubkey, String plain){ return encrypt(pubkey,plain,"RSA"); } static String encrypt(String stringKey, String plain, String algo){ String enc="failed"; try{ byte[] byteKey = new BASE64Decoder().decodeBuffer(stringKey); Key key = new SecretKeySpec(byteKey,algo); byte[] data = plain.getBytes(); Cipher c = Cipher.getInstance(algo); c.init(Cipher.ENCRYPT_MODE, key); byte[] encVal = c.doFinal(data); enc = new BASE64Encoder().encode(encVal); }catch(Exception e){e.printStackTrace();} return enc; } ``` However, when it runs, it shows the following error: ``` java.security.InvalidKeyException: No installed provider supports this key: javax.crypto.spec.SecretKeySpec at javax.crypto.Cipher.chooseProvider(Cipher.java:877) at javax.crypto.Cipher.init(Cipher.java:1212) at javax.crypto.Cipher.init(Cipher.java:1152) at Crypto.encrypt(Crypto.java:37) at Crypto.RSAEncrypt(Crypto.java…

Accepted Answer

As was said in the comments, `SecretKeySpec` is for symmetric algorithms only. You mentioned that you got your `byte[]` containing the key by calling `getEncoded`.

There are two possibilities and two resulting formats:

Encoding of an RSA PrivateKey

Calling `PrivateKey#getEncoded` on an instance of an RSA private key will result in a PKCS#8 encoding for private keys, and it can be restored with the help of PKCS8EncodedKeySpec.

Encoding of an RSA PublicKey

`PublicKey#getEncoded` on an RSA public key results in the generic X.509 public key encoding, and can be restored with X509EncodedKeySpec.

Example Usage

```
byte[] data = "test".getBytes("UTF8");
KeyPairGenerator kpg = KeyPairGenerator.getInstance("RSA");
kpg.initialize(512);
KeyPair keyPair = kpg.genKeyPair();
        
byte[] pk = keyPair.getPublic().getEncoded();
X509EncodedKeySpec spec = new X509EncodedKeySpec(pk);
KeyFactory keyFactory = KeyFactory.getInstance("RSA");
PublicKey pubKey = keyFactory.generatePublic(spec);
Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");
cipher.init(Cipher.ENCRYPT_MODE, pubKey);
byte[] encrypted = cipher.doFinal(data);
        
byte[] priv = keyPair.getPrivate().getEncoded();
PKCS8EncodedKeySpec spec2 = new PKCS8EncodedKeySpec(priv);
PrivateKey privKey = keyFactory.generatePrivate(spec2);
cipher.init(Cipher.DECRYPT_MODE, privKey);
byte[] plain = cipher.doFinal(encrypted);
        
System.out.println(new String(plain, "UTF8")); //=> "test"
```

Using RSA encryption in Java without BouncyCastle

Solution

Problem