ring/io/
der.rs

Help
1// Copyright 2015 Brian Smith.
2//
3// Permission to use, copy, modify, and/or distribute this software for any
4// purpose with or without fee is hereby granted, provided that the above
5// copyright notice and this permission notice appear in all copies.
6//
7// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
8// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
9// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
10// SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
11// WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
12// OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
13// CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
14
15//! Building blocks for parsing DER-encoded ASN.1 structures.
16//!
17//! This module contains the foundational parts of an ASN.1 DER parser.
18
19use super::Positive;
20use crate::error;
21
22pub const CONSTRUCTED: u8 = 1 << 5;
23pub const CONTEXT_SPECIFIC: u8 = 2 << 6;
24
25#[derive(Clone, Copy, PartialEq)]
26#[repr(u8)]
27pub enum Tag {
28    Boolean = 0x01,
29    Integer = 0x02,
30    BitString = 0x03,
31    OctetString = 0x04,
32    Null = 0x05,
33    OID = 0x06,
34    Sequence = CONSTRUCTED | 0x10, // 0x30
35    UTCTime = 0x17,
36    GeneralizedTime = 0x18,
37
38    ContextSpecific1 = CONTEXT_SPECIFIC | 1,
39
40    ContextSpecificConstructed0 = CONTEXT_SPECIFIC | CONSTRUCTED | 0,
41    ContextSpecificConstructed1 = CONTEXT_SPECIFIC | CONSTRUCTED | 1,
42    ContextSpecificConstructed3 = CONTEXT_SPECIFIC | CONSTRUCTED | 3,
43}
44
45impl From<Tag> for usize {
46    fn from(tag: Tag) -> Self {
47        Self::from(Tag::into(tag))
48    }
49}
50
51impl From<Tag> for u8 {
52    fn from(tag: Tag) -> Self {
53        Tag::into(tag)
54    }
55}
56
57// `impl From<Tag> for u8` but as a `const fn`.
58impl Tag {
59    pub const fn into(self) -> u8 {
60        self as u8
61    }
62}
63
64pub fn expect_tag_and_get_value<'a>(
65    input: &mut untrusted::Reader<'a>,
66    tag: Tag,
67) -> Result<untrusted::Input<'a>, error::Unspecified> {
68    let (actual_tag, inner) = read_tag_and_get_value(input)?;
69    if usize::from(tag) != usize::from(actual_tag) {
70        return Err(error::Unspecified);
71    }
72    Ok(inner)
73}
74
75pub fn read_tag_and_get_value<'a>(
76    input: &mut untrusted::Reader<'a>,
77) -> Result<(u8, untrusted::Input<'a>), error::Unspecified> {
78    let tag = input.read_byte()?;
79    if (tag & 0x1F) == 0x1F {
80        return Err(error::Unspecified); // High tag number form is not allowed.
81    }
82
83    // If the high order bit of the first byte is set to zero then the length
84    // is encoded in the seven remaining bits of that byte. Otherwise, those
85    // seven bits represent the number of bytes used to encode the length.
86    let length = match input.read_byte()? {
87        n if (n & 0x80) == 0 => usize::from(n),
88        0x81 => {
89            let second_byte = input.read_byte()?;
90            if second_byte < 128 {
91                return Err(error::Unspecified); // Not the canonical encoding.
92            }
93            usize::from(second_byte)
94        }
95        0x82 => {
96            let second_byte = usize::from(input.read_byte()?);
97            let third_byte = usize::from(input.read_byte()?);
98            let combined = (second_byte << 8) | third_byte;
99            if combined < 256 {
100                return Err(error::Unspecified); // Not the canonical encoding.
101            }
102            combined
103        }
104        _ => {
105            return Err(error::Unspecified); // We don't support longer lengths.
106        }
107    };
108
109    let inner = input.read_bytes(length)?;
110    Ok((tag, inner))
111}
112
113#[inline]
114pub fn bit_string_with_no_unused_bits<'a>(
115    input: &mut untrusted::Reader<'a>,
116) -> Result<untrusted::Input<'a>, error::Unspecified> {
117    bit_string_tagged_with_no_unused_bits(Tag::BitString, input)
118}
119
120pub(crate) fn bit_string_tagged_with_no_unused_bits<'a>(
121    tag: Tag,
122    input: &mut untrusted::Reader<'a>,
123) -> Result<untrusted::Input<'a>, error::Unspecified> {
124    nested(input, tag, error::Unspecified, |value| {
125        let unused_bits_at_end = value.read_byte().map_err(|_| error::Unspecified)?;
126        if unused_bits_at_end != 0 {
127            return Err(error::Unspecified);
128        }
129        Ok(value.read_bytes_to_end())
130    })
131}
132
133// TODO: investigate taking decoder as a reference to reduce generated code
134// size.
135pub fn nested<'a, F, R, E: Copy>(
136    input: &mut untrusted::Reader<'a>,
137    tag: Tag,
138    error: E,
139    decoder: F,
140) -> Result<R, E>
141where
142    F: FnOnce(&mut untrusted::Reader<'a>) -> Result<R, E>,
143{
144    let inner = expect_tag_and_get_value(input, tag).map_err(|_| error)?;
145    inner.read_all(error, decoder)
146}
147
148pub(crate) fn nonnegative_integer<'a>(
149    input: &mut untrusted::Reader<'a>,
150) -> Result<untrusted::Input<'a>, error::Unspecified> {
151    let value = expect_tag_and_get_value(input, Tag::Integer)?;
152    match value
153        .as_slice_less_safe()
154        .split_first()
155        .ok_or(error::Unspecified)?
156    {
157        // Zero or leading zero.
158        (0, rest) => {
159            match rest.first() {
160                // Zero.
161                None => Ok(value),
162                // Necessary leading zero.
163                Some(&second) if second & 0x80 == 0x80 => Ok(untrusted::Input::from(rest)),
164                // Unnecessary leading zero.
165                _ => Err(error::Unspecified),
166            }
167        }
168        // Positive value with no leading zero.
169        (first, _) if first & 0x80 == 0 => Ok(value),
170        // Negative value.
171        (_, _) => Err(error::Unspecified),
172    }
173}
174
175/// Parse as integer with a value in the in the range [0, 255], returning its
176/// numeric value. This is typically used for parsing version numbers.
177#[inline]
178pub fn small_nonnegative_integer(input: &mut untrusted::Reader) -> Result<u8, error::Unspecified> {
179    let value = nonnegative_integer(input)?;
180    match *value.as_slice_less_safe() {
181        [b] => Ok(b),
182        _ => Err(error::Unspecified),
183    }
184}
185
186/// Parses a positive DER integer, returning the big-endian-encoded value,
187/// sans any leading zero byte.
188pub fn positive_integer<'a>(
189    input: &mut untrusted::Reader<'a>,
190) -> Result<Positive<'a>, error::Unspecified> {
191    let value = nonnegative_integer(input)?;
192    Positive::from_be_bytes(value)
193}
194
195#[cfg(test)]
196mod tests {
197    use super::*;
198    use crate::error;
199
200    fn with_i<'a, F, R>(value: &'a [u8], f: F) -> Result<R, error::Unspecified>
201    where
202        F: FnOnce(&mut untrusted::Reader<'a>) -> Result<R, error::Unspecified>,
203    {
204        untrusted::Input::from(value).read_all(error::Unspecified, f)
205    }
206
207    static ZERO_INTEGER: &[u8] = &[0x02, 0x01, 0x00];
208
209    static GOOD_POSITIVE_INTEGERS_SMALL: &[(&[u8], u8)] = &[
210        (&[0x02, 0x01, 0x01], 0x01),
211        (&[0x02, 0x01, 0x02], 0x02),
212        (&[0x02, 0x01, 0x7e], 0x7e),
213        (&[0x02, 0x01, 0x7f], 0x7f),
214        // Values that need to have an 0x00 prefix to disambiguate them from
215        // them from negative values.
216        (&[0x02, 0x02, 0x00, 0x80], 0x80),
217        (&[0x02, 0x02, 0x00, 0x81], 0x81),
218        (&[0x02, 0x02, 0x00, 0xfe], 0xfe),
219        (&[0x02, 0x02, 0x00, 0xff], 0xff),
220    ];
221
222    static GOOD_POSITIVE_INTEGERS_LARGE: &[(&[u8], &[u8])] = &[
223        (&[0x02, 0x02, 0x01, 0x00], &[0x01, 0x00]),
224        (&[0x02, 0x02, 0x02, 0x01], &[0x02, 0x01]),
225        (&[0x02, 0x02, 0x7e, 0xfe], &[0x7e, 0xfe]),
226        (&[0x02, 0x02, 0x7f, 0xff], &[0x7f, 0xff]),
227        // Values that need to have an 0x00 prefix to disambiguate them from
228        // them from negative values.
229        (&[0x02, 0x03, 0x00, 0x80, 0x00], &[0x80, 0x00]),
230        (&[0x02, 0x03, 0x00, 0x81, 0x01], &[0x81, 0x01]),
231        (&[0x02, 0x03, 0x00, 0xfe, 0xfe], &[0xfe, 0xfe]),
232        (&[0x02, 0x03, 0x00, 0xff, 0xff], &[0xff, 0xff]),
233    ];
234
235    static BAD_NONNEGATIVE_INTEGERS: &[&[u8]] = &[
236        &[],           // At end of input
237        &[0x02],       // Tag only
238        &[0x02, 0x00], // Empty value
239        // Length mismatch
240        &[0x02, 0x00, 0x01],
241        &[0x02, 0x01],
242        // Would be valid if leading zero is ignored when comparing length.
243        &[0x02, 0x01, 0x00, 0x01],
244        &[0x02, 0x01, 0x01, 0x00], // Would be valid if last byte is ignored.
245        &[0x02, 0x02, 0x01],
246        // Values that are missing a necessary leading 0x00
247        &[0x02, 0x01, 0x80],
248        &[0x02, 0x01, 0x81],
249        &[0x02, 0x01, 0xfe],
250        &[0x02, 0x01, 0xff],
251        // Values that have an unnecessary leading 0x00
252        &[0x02, 0x02, 0x00, 0x00],
253        &[0x02, 0x02, 0x00, 0x01],
254        &[0x02, 0x02, 0x00, 0x02],
255        &[0x02, 0x02, 0x00, 0x7e],
256        &[0x02, 0x02, 0x00, 0x7f],
257    ];
258
259    #[test]
260    fn test_small_nonnegative_integer() {
261        let zero = (ZERO_INTEGER, 0x00);
262        for &(test_in, test_out) in
263            core::iter::once(&zero).chain(GOOD_POSITIVE_INTEGERS_SMALL.iter())
264        {
265            let result = with_i(test_in, |input| {
266                assert_eq!(small_nonnegative_integer(input)?, test_out);
267                Ok(())
268            });
269            assert_eq!(result, Ok(()));
270        }
271        for &test_in in BAD_NONNEGATIVE_INTEGERS
272            .iter()
273            .chain(GOOD_POSITIVE_INTEGERS_LARGE.iter().map(|(input, _)| input))
274        {
275            let result = with_i(test_in, small_nonnegative_integer);
276            assert_eq!(result, Err(error::Unspecified));
277        }
278    }
279
280    #[test]
281    fn test_positive_integer() {
282        for (test_in, test_out) in GOOD_POSITIVE_INTEGERS_SMALL
283            .iter()
284            .map(|(test_in, test_out)| (*test_in, core::slice::from_ref(test_out)))
285            .chain(GOOD_POSITIVE_INTEGERS_LARGE.iter().copied())
286        {
287            let result = with_i(test_in, |input| {
288                assert_eq!(
289                    positive_integer(input)?.big_endian_without_leading_zero(),
290                    test_out
291                );
292                Ok(())
293            });
294            assert_eq!(result, Ok(()))
295        }
296        for &test_in in core::iter::once(&ZERO_INTEGER).chain(BAD_NONNEGATIVE_INTEGERS.iter()) {
297            let result = with_i(test_in, positive_integer);
298            assert!(matches!(result, Err(error::Unspecified)));
299        }
300    }
301}
ring/io/der.rs

ring/io/
der.rs
