Objective-C

    NSString *plainString = @"foo";

    Encoding

    NSData *plainData = [plainString dataUsingEncoding:NSUTF8StringEncoding];

    NSString *base64String = [plainData base64EncodedStringWithOptions:0];

    NSLog(@"%@", base64String); // Zm9v

    Decoding

    NSData *decodedData = [[NSData alloc] initWithBase64EncodedString:base64String options:0];

    NSString *decodedString = [[NSString alloc] initWithData:decodedData encoding:NSUTF8StringEncoding];

    NSLog(@"%@", decodedString); // foo

    Swift

    let plainString = "foo"

    Encoding

    let plainData = plainString.dataUsingEncoding(NSUTF8StringEncoding)

    let base64String = plainData?.base64EncodedStringWithOptions(.allZeros)

    println(base64String!) // Zm9v

    Decoding

    let decodedData = NSData(base64EncodedString: base64String!, options: .allZeros)

    let decodedString = NSString(data: decodedData, encoding: NSUTF8StringEncoding)

    println(decodedString) // foo