litcrypt 0.2.0

Let's encrypt your string statically during compile time
Documentation 
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//! A repeating-key XOR functions.
//!
//! This functions might be useful to play with
//! [the matasano crypto challenges](http://cryptopals.com).
//! 
//! 

//
// Copyright (c) 2014 Aleksey Kuznetsov
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all
// copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

/// Returns result of a XOR operation applied to a `source` byte sequence.
///
/// `key` will be an infinitely repeating byte sequence.
pub fn xor(source: &[u8], key: &[u8]) -> Vec<u8> {
    match key.len() {
        0 => source.into(),
        1 => xor_with_byte(source, key[0]),
        _ => {
            let key_iter = InfiniteByteIterator::new(key);
            source.iter().zip(key_iter).map(|(&a, b)| a ^ b).collect()
        }
    }
}

/// Returns result of a XOR operation applied to a `source` byte sequence.
///
/// `byte` will be an infinitely repeating byte sequence.
pub fn xor_with_byte(source: &[u8], byte: u8) -> Vec<u8> {
    source.iter().map(|&a| a ^ byte).collect()
}

struct InfiniteByteIterator<'a> {
    bytes: &'a [u8],
    index: usize,
}

impl<'a> InfiniteByteIterator<'a> {
    pub fn new(bytes: &'a [u8]) -> InfiniteByteIterator<'a> {
        InfiniteByteIterator {
            bytes: bytes,
            index: 0,
        }
    }
}

impl<'a> Iterator for InfiniteByteIterator<'a> {
    type Item = u8;
    fn next(&mut self) -> Option<u8> {
        let byte = self.bytes[self.index];
        self.index = next_index(self.index, self.bytes.len());
        Some(byte)
    }
}

fn next_index(index: usize, count: usize) -> usize {
    if index + 1 < count {
        index + 1
    } else {
        0
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::expectest::prelude::*;

    #[test]
    fn xor_valid_result() {
        let source = &[0, 1, 2, 3];
        let result = xor(source, &[34, 52]);
        expect!(result).to(be_equal_to([34, 53, 32, 55]));
    }

    #[test]
    fn xor_valid_result_with_one_byte() {
        let source = &[0, 1, 2, 3];
        let result = xor(source, &[47]);
        expect!(result).to(be_equal_to([47, 46, 45, 44]));
    }

    #[test]
    fn xor_empty_key() {
        let source = &[0, 1, 2, 3];
        let result = xor(source, &[]);
        expect!(result).to(be_equal_to(source));
    }

    #[test]
    fn xor_empty_source() {
        let source = &[];
        let result = xor(source, &[45, 32, 56]);
        expect!(result.iter()).to(be_empty());
    }

    #[test]
    fn xor_with_byte_valid_result() {
        let source = &[0, 1, 2, 3];
        let result = xor_with_byte(source, 23);
        expect!(result).to(be_equal_to([23, 22, 21, 20]));
    }
}