1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160

//! This crate provides trait for Message Authentication Code (MAC) algorithms.

#![no_std]
#![cfg_attr(docsrs, feature(doc_cfg))]
#![doc(
    html_logo_url = "https://raw.githubusercontent.com/RustCrypto/meta/master/logo.svg",
    html_favicon_url = "https://raw.githubusercontent.com/RustCrypto/meta/master/logo.svg",
    html_root_url = "https://docs.rs/crypto-mac/0.11.1"
)]
#![forbid(unsafe_code)]
#![warn(missing_docs, rust_2018_idioms)]

#[cfg(feature = "std")]
extern crate std;

#[cfg(feature = "cipher")]
pub use cipher;
#[cfg(feature = "cipher")]
use cipher::{BlockCipher, NewBlockCipher};

#[cfg(feature = "dev")]
#[cfg_attr(docsrs, doc(cfg(feature = "dev")))]
pub mod dev;

mod errors;

pub use crate::errors::{InvalidKeyLength, MacError};
pub use generic_array::{self, typenum::consts};

use generic_array::typenum::Unsigned;
use generic_array::{ArrayLength, GenericArray};
use subtle::{Choice, ConstantTimeEq};

/// Key for an algorithm that implements [`NewMac`].
pub type Key<M> = GenericArray<u8, <M as NewMac>::KeySize>;

/// Instantiate a [`Mac`] algorithm.
pub trait NewMac: Sized {
    /// Key size in bytes with which cipher guaranteed to be initialized.
    type KeySize: ArrayLength<u8>;

    /// Initialize new MAC instance from key with fixed size.
    fn new(key: &Key<Self>) -> Self;

    /// Initialize new MAC instance from key with variable size.
    ///
    /// Default implementation will accept only keys with length equal to
    /// `KeySize`, but some MACs can accept range of key lengths.
    fn new_from_slice(key: &[u8]) -> Result<Self, InvalidKeyLength> {
        if key.len() != Self::KeySize::to_usize() {
            Err(InvalidKeyLength)
        } else {
            Ok(Self::new(GenericArray::from_slice(key)))
        }
    }
}

/// The [`Mac`] trait defines methods for a Message Authentication algorithm.
pub trait Mac: Clone {
    /// Output size of the [[`Mac`]]
    type OutputSize: ArrayLength<u8>;

    /// Update MAC state with the given data.
    fn update(&mut self, data: &[u8]);

    /// Reset [`Mac`] instance.
    fn reset(&mut self);

    /// Obtain the result of a [`Mac`] computation as a [`Output`] and consume
    /// [`Mac`] instance.
    fn finalize(self) -> Output<Self>;

    /// Obtain the result of a [`Mac`] computation as a [`Output`] and reset
    /// [`Mac`] instance.
    fn finalize_reset(&mut self) -> Output<Self> {
        let res = self.clone().finalize();
        self.reset();
        res
    }

    /// Check if tag/code value is correct for the processed input.
    fn verify(self, tag: &[u8]) -> Result<(), MacError> {
        let choice = self.finalize().bytes.ct_eq(tag);

        if choice.unwrap_u8() == 1 {
            Ok(())
        } else {
            Err(MacError)
        }
    }
}

/// [`Output`] is a thin wrapper around bytes array which provides a safe `Eq`
/// implementation that runs in a fixed time.
#[derive(Clone)]
pub struct Output<M: Mac> {
    bytes: GenericArray<u8, M::OutputSize>,
}

impl<M: Mac> Output<M> {
    /// Create a new MAC [`Output`].
    pub fn new(bytes: GenericArray<u8, M::OutputSize>) -> Output<M> {
        Output { bytes }
    }

    /// Get the MAC tag/code value as a byte array.
    ///
    /// Be very careful using this method, since incorrect use of the tag value
    /// may permit timing attacks which defeat the security provided by the
    /// [`Mac`] trait.
    pub fn into_bytes(self) -> GenericArray<u8, M::OutputSize> {
        self.bytes
    }
}

impl<M: Mac> ConstantTimeEq for Output<M> {
    fn ct_eq(&self, other: &Self) -> Choice {
        self.bytes.ct_eq(&other.bytes)
    }
}

impl<M: Mac> PartialEq for Output<M> {
    fn eq(&self, x: &Output<M>) -> bool {
        self.ct_eq(x).unwrap_u8() == 1
    }
}

impl<M: Mac> Eq for Output<M> {}

#[cfg(feature = "cipher")]
#[cfg_attr(docsrs, doc(cfg(feature = "cipher")))]
/// Trait for MAC functions which can be created from block cipher.
pub trait FromBlockCipher {
    /// Block cipher type
    type Cipher: BlockCipher;

    /// Create new MAC isntance from provided block cipher.
    fn from_cipher(cipher: Self::Cipher) -> Self;
}

#[cfg(feature = "cipher")]
#[cfg_attr(docsrs, doc(cfg(feature = "cipher")))]
impl<T> NewMac for T
where
    T: FromBlockCipher,
    T::Cipher: NewBlockCipher,
{
    type KeySize = <<Self as FromBlockCipher>::Cipher as NewBlockCipher>::KeySize;

    fn new(key: &Key<Self>) -> Self {
        let cipher = <Self as FromBlockCipher>::Cipher::new(key);
        Self::from_cipher(cipher)
    }

    fn new_from_slice(key: &[u8]) -> Result<Self, InvalidKeyLength> {
        <Self as FromBlockCipher>::Cipher::new_from_slice(key)
            .map_err(|_| InvalidKeyLength)
            .map(Self::from_cipher)
    }
}