I have generated on my android application a pair of RSA Keys.
I receive from a web service
- an AES Key, encrypted with my RSA public key
- a String encoded with the AES key.
So I must do the following:
- decrypt the AES Key
- decrypt the string with the obtained AES Key.
To generate the RSA Keys I did:
keyGen = KeyPairGenerator.getInstance("RSA");
keyGen.initialize(size);
keypair = keyGen.genKeyPair();
privateKey = keypair.getPrivate();
publicKey = keypair.getPublic();
On RSA decrypt I use :
public static byte[] decryptRSA( PrivateKey key, byte[] text) throws
Exception
{
byte[] dectyptedText = null;
Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS7Padding");
cipher.init(Cipher.DECRYPT_MODE, key);
dectyptedText = cipher.doFinal(text);
return dectyptedText;
}
On AES decrypt I use:
public static byte[] decryptAES(byte[] key, byte[] text) throws
Exception {
SecretKeySpec skeySpec = new SecretKeySpec(key,
"AES");
Cipher cipher = Cipher.getInstance("AES/ECB/
PKCS7Padding");
cipher.init(Cipher.DECRYPT_MODE, skeySpec);
byte[] decrypted = cipher.doFinal(text);
return decrypted;
}
So, in my code, to obtain the decrypted AES Key I do
byte[] decryptedAESKey = sm.decryptRSA(key,
Base64.decode(ReceivedBase64EncryptedAESKey));
byte[] decryptedString = sm.decryptAES(decryptedAESKey,
Base64.decode(ReceivedEncryptedAESString));[/
>From the web service I get the ReceivedEncryptedAESString=
qjYcPCHkFpbTjntDCpXCGabSY5DFH... and the decryptedAESKey looks like:
[121, 98, 51, 100, 108, 112, 118, 107, 118, 97]
The problem appears to be on cipher.init(Cipher.DECRYPT_MODE,
skeySpec); as it throws an exception: InvalidKeyException: Key length
not 128/192/256 bits. Maybe I do RSA decryption wrong ?
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