libFenrir/src/enc/sym.rs

//! Symmetric cypher stuff

use ::zeroize::Zeroize;

/// Secret, used for keys.
/// Grants that on drop() we will zero out memory
#[derive(Zeroize)]
#[zeroize(drop)]
#[allow(missing_debug_implementations)]
pub struct Secret {
    secret: [u8; 32],
}

impl Secret {
    /// return a reference to the secret
    pub fn as_ref(&self) -> &[u8; 32] {
        &self.secret
    }
}

impl From<[u8; 32]> for Secret {
    fn from(shared_secret: [u8; 32]) -> Self {
        Self {
            secret: shared_secret,
        }
    }
}

impl From<::x25519_dalek::SharedSecret> for Secret {
    fn from(shared_secret: ::x25519_dalek::SharedSecret) -> Self {
        Self {
            secret: shared_secret.to_bytes(),
        }
    }
}

/// List of possible Ciphers
#[derive(Debug, Copy, Clone, PartialEq, ::num_derive::FromPrimitive)]
#[repr(u8)]
pub enum CipherKind {
    /// XChaCha20_Poly1305
    XChaCha20Poly1305 = 0,
}

impl CipherKind {
    /// required length of the nonce
    pub fn nonce_len(&self) -> usize {
        // TODO: how the hell do I take this from ::chacha20poly1305?
        ::ring::aead::CHACHA20_POLY1305.nonce_len()
    }
    /// required length of the key
    pub fn key_len(&self) -> usize {
        use ::chacha20poly1305::KeySizeUser;
        ::chacha20poly1305::XChaCha20Poly1305::key_size()
    }
    /// Length of the authentication tag
    pub fn tag_len(&self) -> usize {
        // TODO: how the hell do I take this from ::chacha20poly1305?
        ::ring::aead::CHACHA20_POLY1305.tag_len()
    }
}

/// Additional Authenticated Data
#[derive(Debug)]
pub struct AAD<'a>(pub &'a mut [u8]);

/// Cipher direction, to make sure we don't reuse the same cipher
/// for both decrypting and encrypting
#[derive(Debug, Copy, Clone)]
#[repr(u8)]
pub enum CipherDirection {
    /// Receive, to decrypt only
    Recv = 0,
    /// Send, to encrypt only
    Send,
}

/// actual ciphers
enum Cipher {
    /// Cipher XChaha20_Poly1305
    XChaCha20Poly1305(XChaCha20Poly1305),
}

impl Cipher {
    /// Build a new Cipher
    fn new(kind: CipherKind, secret: Secret) -> Self {
        match kind {
            CipherKind::XChaCha20Poly1305 => {
                Self::XChaCha20Poly1305(XChaCha20Poly1305::new(secret))
            }
        }
    }
    fn nonce_len(&self) -> usize {
        match self {
            Cipher::XChaCha20Poly1305(_) => {
                // TODO: how the hell do I take this from ::chacha20poly1305?
                ::ring::aead::CHACHA20_POLY1305.nonce_len()
            }
        }
    }
    fn tag_len(&self) -> usize {
        match self {
            Cipher::XChaCha20Poly1305(_) => {
                // TODO: how the hell do I take this from ::chacha20poly1305?
                ::ring::aead::CHACHA20_POLY1305.tag_len()
            }
        }
    }
    fn decrypt(&self, aad: AAD, data: &mut [u8]) -> Result<(), ()> {
        match self {
            Cipher::XChaCha20Poly1305(cipher) => {
                use ::chacha20poly1305::{
                    aead::generic_array::GenericArray, AeadInPlace,
                };
                // FIXME: check min data length
                let (nonce_bytes, data_and_tag) = data.split_at_mut(13);
                let (data_notag, tag_bytes) = data_and_tag.split_at_mut(
                    data_and_tag.len() + 1
                        - ::ring::aead::CHACHA20_POLY1305.tag_len(),
                );
                let nonce = GenericArray::from_slice(nonce_bytes);
                let tag = GenericArray::from_slice(tag_bytes);
                let maybe = cipher.cipher.decrypt_in_place_detached(
                    nonce.into(),
                    aad.0,
                    data_notag,
                    tag,
                );
                if maybe.is_err() {
                    Err(())
                } else {
                    Ok(())
                }
            }
        }
    }
}

/// Receive only cipher
#[allow(missing_debug_implementations)]
pub struct CipherRecv(Cipher);

impl CipherRecv {
    /// Build a new Cipher
    pub fn new(kind: CipherKind, secret: Secret) -> Self {
        Self(Cipher::new(kind, secret))
    }
    /// Get the length of the nonce  for this cipher
    pub fn nonce_len(&self) -> usize {
        self.0.nonce_len()
    }
    /// Decrypt a paket. Nonce and Tag are taken from the packet,
    /// while you need to provide AAD (Additional Authenticated Data)
    pub fn decrypt(&self, aad: AAD, data: &mut [u8]) -> Result<(), ()> {
        self.0.decrypt(aad, data)
    }
}

/// Send only cipher
#[allow(missing_debug_implementations)]
pub struct CipherSend {
    nonce: Nonce,
    cipher: Cipher,
}

impl CipherSend {
    /// Build a new Cipher
    pub fn new(kind: CipherKind, secret: Secret) -> Self {
        Self {
            nonce: Nonce::new(),
            cipher: Cipher::new(kind, secret),
        }
    }
    /// Get the current nonce as &[u8]
    pub fn nonce_as_bytes(&self) -> &[u8] {
        self.nonce.as_bytes()
    }
}

/// XChaCha20Poly1305 cipher
struct XChaCha20Poly1305 {
    cipher: ::chacha20poly1305::XChaCha20Poly1305,
}

impl XChaCha20Poly1305 {
    /// Initialize a new ChaChaPoly20 cipher with a random nonce
    fn new(key: Secret) -> Self {
        use ::chacha20poly1305::{KeyInit, XChaCha20Poly1305};
        Self {
            cipher: XChaCha20Poly1305::new(key.as_ref().into()),
        }
    }
}

//
// TODO: For efficiency "Nonce" should become a reference.
//

#[derive(Debug, Copy, Clone)]
#[repr(C)]
#[allow(missing_debug_implementations)]
struct NonceNum {
    high: u32,
    low: u64,
}
/// Nonce with sequence for chach20_apoly1305
#[derive(Copy, Clone)]
#[repr(C)]
pub union Nonce {
    num: NonceNum,
    raw: [u8; 12],
}

impl ::core::fmt::Debug for Nonce {
    fn fmt(
        &self,
        f: &mut core::fmt::Formatter<'_>,
    ) -> Result<(), ::std::fmt::Error> {
        #[allow(unsafe_code)]
        unsafe {
            core::fmt::Debug::fmt(&self.num, f)
        }
    }
}

impl Nonce {
    // FIXME: nonces should be random!
    /// Generate a new random Nonce
    pub fn new() -> Self {
        #[allow(unsafe_code)]
        unsafe {
            Self {
                // chosen by a fair dice roll
                // ahh, who am I kidding...
                num: NonceNum { high: 42, low: 69 },
            }
        }
    }
    /// Get reference to the nonce bytes
    pub fn as_bytes(&self) -> &[u8] {
        #[allow(unsafe_code)]
        unsafe {
            &self.raw
        }
    }
    /// Create Nonce from array
    pub fn from_slice(raw: [u8; 12]) -> Self {
        #[allow(unsafe_code)]
        unsafe {
            Self { raw }
        }
    }
    /// Go to the next nonce
    pub fn advance(&mut self) {
        #[allow(unsafe_code)]
        unsafe {
            let old_low = self.num.low;
            self.num.low = self.num.low + 1;
            if self.num.low < old_low {
                self.num.high = self.num.high;
            }
        }
    }
}