ring/rsa/
padding.rs

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
// Copyright 2015-2016 Brian Smith.
//
// Permission to use, copy, modify, and/or distribute this software for any
// purpose with or without fee is hereby granted, provided that the above
// copyright notice and this permission notice appear in all copies.
//
// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHORS DISCLAIM ALL WARRANTIES
// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY
// SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
// OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
// CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.

use crate::{bits, digest, error, rand};

mod pkcs1;
mod pss;

pub use self::{
    pkcs1::{PKCS1, RSA_PKCS1_SHA256, RSA_PKCS1_SHA384, RSA_PKCS1_SHA512},
    pss::{PSS, RSA_PSS_SHA256, RSA_PSS_SHA384, RSA_PSS_SHA512},
};
pub(super) use pkcs1::RSA_PKCS1_SHA1_FOR_LEGACY_USE_ONLY;

/// Common features of both RSA padding encoding and RSA padding verification.
pub trait Padding: 'static + Sync + crate::sealed::Sealed + core::fmt::Debug {
    // The digest algorithm used for digesting the message (and maybe for
    // other things).
    fn digest_alg(&self) -> &'static digest::Algorithm;
}

/// An RSA signature encoding as described in [RFC 3447 Section 8].
///
/// [RFC 3447 Section 8]: https://tools.ietf.org/html/rfc3447#section-8
#[cfg(feature = "alloc")]
pub trait RsaEncoding: Padding {
    #[doc(hidden)]
    fn encode(
        &self,
        m_hash: digest::Digest,
        m_out: &mut [u8],
        mod_bits: bits::BitLength,
        rng: &dyn rand::SecureRandom,
    ) -> Result<(), error::Unspecified>;
}

/// Verification of an RSA signature encoding as described in
/// [RFC 3447 Section 8].
///
/// [RFC 3447 Section 8]: https://tools.ietf.org/html/rfc3447#section-8
pub trait Verification: Padding {
    fn verify(
        &self,
        m_hash: digest::Digest,
        m: &mut untrusted::Reader,
        mod_bits: bits::BitLength,
    ) -> Result<(), error::Unspecified>;
}

// Masks `out` with the output of the mask-generating function MGF1 as
// described in https://tools.ietf.org/html/rfc3447#appendix-B.2.1.
fn mgf1(digest_alg: &'static digest::Algorithm, seed: &[u8], out: &mut [u8]) {
    let digest_len = digest_alg.output_len();

    // Maximum counter value is the value of (mask_len / digest_len) rounded up.
    for (i, out) in out.chunks_mut(digest_len).enumerate() {
        let mut ctx = digest::Context::new(digest_alg);
        ctx.update(seed);
        // The counter will always fit in a `u32` because we reject absurdly
        // long inputs very early.
        ctx.update(&u32::to_be_bytes(i.try_into().unwrap()));
        let digest = ctx.finish();
        // `zip` does the right thing as the the last chunk may legitimately be
        // shorter than `digest`, and `digest` will never be shorter than `out`.
        for (m, &d) in out.iter_mut().zip(digest.as_ref().iter()) {
            *m ^= d;
        }
    }
}

#[cfg(test)]
mod test {
    use super::*;
    use crate::{digest, error, test};
    use alloc::vec;

    #[test]
    fn test_pss_padding_verify() {
        test::run(
            test_file!("rsa_pss_padding_tests.txt"),
            |section, test_case| {
                assert_eq!(section, "");

                let digest_name = test_case.consume_string("Digest");
                let alg = match digest_name.as_ref() {
                    "SHA256" => &RSA_PSS_SHA256,
                    "SHA384" => &RSA_PSS_SHA384,
                    "SHA512" => &RSA_PSS_SHA512,
                    _ => panic!("Unsupported digest: {}", digest_name),
                };

                let msg = test_case.consume_bytes("Msg");
                let msg = untrusted::Input::from(&msg);
                let m_hash = digest::digest(alg.digest_alg(), msg.as_slice_less_safe());

                let encoded = test_case.consume_bytes("EM");
                let encoded = untrusted::Input::from(&encoded);

                // Salt is recomputed in verification algorithm.
                let _ = test_case.consume_bytes("Salt");

                let bit_len = test_case.consume_usize_bits("Len");
                let is_valid = test_case.consume_string("Result") == "P";

                let actual_result =
                    encoded.read_all(error::Unspecified, |m| alg.verify(m_hash, m, bit_len));
                assert_eq!(actual_result.is_ok(), is_valid);

                Ok(())
            },
        );
    }

    // Tests PSS encoding for various public modulus lengths.
    #[cfg(feature = "alloc")]
    #[test]
    fn test_pss_padding_encode() {
        test::run(
            test_file!("rsa_pss_padding_tests.txt"),
            |section, test_case| {
                assert_eq!(section, "");

                let digest_name = test_case.consume_string("Digest");
                let alg = match digest_name.as_ref() {
                    "SHA256" => &RSA_PSS_SHA256,
                    "SHA384" => &RSA_PSS_SHA384,
                    "SHA512" => &RSA_PSS_SHA512,
                    _ => panic!("Unsupported digest: {}", digest_name),
                };

                let msg = test_case.consume_bytes("Msg");
                let salt = test_case.consume_bytes("Salt");
                let encoded = test_case.consume_bytes("EM");
                let bit_len = test_case.consume_usize_bits("Len");
                let expected_result = test_case.consume_string("Result");

                // Only test the valid outputs
                if expected_result != "P" {
                    return Ok(());
                }

                let rng = test::rand::FixedSliceRandom { bytes: &salt };

                let mut m_out = vec![0u8; bit_len.as_usize_bytes_rounded_up()];
                let digest = digest::digest(alg.digest_alg(), &msg);
                alg.encode(digest, &mut m_out, bit_len, &rng).unwrap();
                assert_eq!(m_out, encoded);

                Ok(())
            },
        );
    }
}