gpp_decrypt 0.1.1

Decrypts the cpassword from Group Policy Preference files (Groups.xml)
Documentation 
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use openssl::symm::{decrypt, Cipher};

const INIT_V: &[u8; 16] = b"\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00";
const KEY: &[u8; 32] = b"\x4e\x99\x06\xe8\xfc\xb6\x6c\xc9\xfa\xf4\x93\x10\x62\x0f\xfe\xe8\xf4\x96\xe8\x06\xcc\x05\x79\x90\x20\x9b\x09\xa4\x33\xb6\x6c\x1b";

/// Decrypts the provided Group Policy Preference cpassword. Returns `None` if
/// decryption fails.
pub fn gpp_decrypt(mut encrypted_string: String) -> String {
    
    let data: Vec<u8> = loop {

        // pad the string
        encrypted_string.extend(
            // creates an iterator that returns a '=' per iteration
            (0..4 - (encrypted_string.len() % 4)).map(|_| '='));

        // decode it, if it fails print a friendly error message
        match base64::decode(encrypted_string) {
            Ok(data) => break data,
            _ => return "error, input is not a valid base64 string.".to_string(),
        }
    };

    match openssl_decrypt(&data) {
        Some(output) => return output,
        None => return "error, failed to decrypt!".to_string(),
    }
}

fn openssl_decrypt(data: &[u8]) -> Option<String> {
    decrypt(Cipher::aes_256_cbc(), KEY, Some(INIT_V), data)
        .ok()
        .and_then(|dec| String::from_utf8(dec).ok())
}