decrytption in ios 7 not working using aes - objective-c

Question

In My App, i'm getting data from xml, where it is encrypted, and i need to decrypt the received nsstring,
UserName = #"QEjbHvzPjk+YuLDVPUJuEA==";
I Need to decrypt this nsstring into regular format, i searched and find aes , but it doesn't make any changes,
NSString* msg = [FBEncryptorAES decryptBase64String:UserName
keyString:#"01234567890abcdefghijklmnopqrstuvwxyz"];
if (msg)
{
UserName = msg;
NSLog(#"decrypted: %#", msg);
} else
{
UserName = #"(failed to decrypt)";
}
How can i decrypt the above nsstring, Thanks in Advance.

Answer 1

The string is not only AES encrypted, it is Base64 encoded. The trailing "==" is typical of base64 padding. Also AES encryption produces data bytes, not ASCII characters and the output is a multiple of the block size. It is common to Base64 encode the result of encryption so it is ASCII and can be included in XML.
For iOS 7 there are several Base64 API methods for NSData. Probably what you want is:
- (id)initWithBase64EncodedString:(NSString *)base64String options:(NSDataBase64DecodingOptions)options
Example:
NSString *userName = #"QEjbHvzPjk+YuLDVPUJuEA==";
NSData *data = [[NSData alloc] initWithBase64EncodedString:userName options:0];
NSLog(#"data: %#", data);
NSLog output:
data: <4048db1e fccf8e4f 98b8b0d5 3d426e10>
The data probably is AES encrypted, it is a multiple of block length, and if so you will need the key and also information on padding, mode and possibly iv.
Note that the FBEncryptorAES class method encryptedBase64String does accept Base64 input but the decryption key string is suspect and the encryption may not match this decryption method due to method and possible iv. So the FBEncryptorAES class may not be what you need.