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
161
162
163
164
165
166
167

// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0

//! Defines the Stateless Reset token

use s2n_codec::{decoder_value, Encoder, EncoderValue};
use subtle::ConstantTimeEq;

//= https://www.rfc-editor.org/rfc/rfc9000#section-10.3
//# Stateless Reset {
//#   Fixed Bits (2) = 1,
//#   Unpredictable Bits (38..),
//#   Stateless Reset Token (128),
//# }
pub const LEN: usize = 128 / 8;

// The implemented PartialEq will have the same results as
// a derived version, except it is constant-time. Therefore
// Hash can still be derived.
#[allow(clippy::derived_hash_with_manual_eq)]
#[derive(Copy, Clone, Debug, Eq, Hash)]
#[cfg_attr(
    any(test, feature = "generator"),
    derive(bolero_generator::TypeGenerator)
)]
pub struct Token([u8; LEN]);

impl Token {
    /// A zeroed out stateless reset token
    pub const ZEROED: Self = Self([0; LEN]);

    /// Unwraps this token, returning the underlying array
    pub fn into_inner(self) -> [u8; LEN] {
        self.0
    }
}

impl From<[u8; LEN]> for Token {
    fn from(bytes: [u8; LEN]) -> Self {
        Self(bytes)
    }
}

impl TryFrom<&[u8]> for Token {
    type Error = core::array::TryFromSliceError;

    fn try_from(bytes: &[u8]) -> Result<Self, Self::Error> {
        let bytes = bytes.try_into()?;
        Ok(Self(bytes))
    }
}

impl AsRef<[u8]> for Token {
    fn as_ref(&self) -> &[u8] {
        &self.0[..]
    }
}

impl AsMut<[u8]> for Token {
    fn as_mut(&mut self) -> &mut [u8] {
        self.0.as_mut()
    }
}

impl PartialEq for Token {
    //= https://www.rfc-editor.org/rfc/rfc9000#section-10.3.1
    //# When comparing a datagram to stateless reset token values, endpoints
    //# MUST perform the comparison without leaking information about the
    //# value of the token.
    fn eq(&self, other: &Self) -> bool {
        self.0.ct_eq(&other.0).into()
    }
}

decoder_value!(
    impl<'a> Token {
        fn decode(buffer: Buffer) -> Result<Self> {
            let (value, buffer) = buffer.decode_slice(LEN)?;
            let value: &[u8] = value.into_less_safe_slice();
            let token = Token::try_from(value).expect("slice len already verified");

            Ok((token, buffer))
        }
    }
);

impl EncoderValue for Token {
    fn encoding_size(&self) -> usize {
        LEN
    }

    fn encode<E: Encoder>(&self, encoder: &mut E) {
        self.as_ref().encode(encoder)
    }
}

// A generator for a stateless reset token
pub trait Generator: 'static + Send {
    /// If enabled, a stateless reset packet containing the token generated
    /// by this Generator will be sent when a packet is received that cannot
    /// be matched to an existing connection. Otherwise, the packet will be
    /// dropped with no further action.
    const ENABLED: bool = true;

    /// Generates a stateless reset token.
    ///
    /// The stateless reset token MUST be difficult to guess.
    ///
    /// To enable stateless reset functionality, the stateless reset token must
    /// be generated the same for a given `local_connection_id` before and after loss of state.
    fn generate(&mut self, local_connection_id: &[u8]) -> Token;
}

#[cfg(any(test, feature = "testing"))]
pub mod testing {
    use crate::{
        stateless_reset,
        stateless_reset::token::{Token, LEN},
    };

    pub const TEST_TOKEN_1: Token = Token(11111111123456578987654321u128.to_be_bytes());
    pub const TEST_TOKEN_2: Token = Token(222222222123456578987654321u128.to_be_bytes());
    pub const TEST_TOKEN_3: Token = Token(333333333123456578987654321u128.to_be_bytes());
    pub const TEST_TOKEN_4: Token = Token(444444444123456578987654321u128.to_be_bytes());

    const KEY: u8 = 123;

    #[derive(Debug, Default)]
    pub struct Generator();

    impl stateless_reset::token::Generator for Generator {
        fn generate(&mut self, connection_id: &[u8]) -> Token {
            let mut token = [0; LEN];

            for (index, byte) in connection_id.as_ref().iter().enumerate() {
                token[index] = byte ^ KEY;
            }

            token.into()
        }
    }
}

#[cfg(test)]
mod tests {
    use crate::stateless_reset::token::{testing::TEST_TOKEN_1, LEN};

    //= https://www.rfc-editor.org/rfc/rfc9000#section-10.3.1
    //= type=test
    //# When comparing a datagram to stateless reset token values, endpoints
    //# MUST perform the comparison without leaking information about the
    //# value of the token.
    #[test]
    fn equality_test() {
        let token_1 = TEST_TOKEN_1;
        let token_2 = TEST_TOKEN_1;

        assert_eq!(token_1, token_2);

        for i in 0..LEN {
            let mut token = TEST_TOKEN_1;
            token.0[i] = !TEST_TOKEN_1.0[i];

            assert_ne!(TEST_TOKEN_1, token);
        }
    }
}