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 AUTHORS DISCLAIM ALL WARRANTIES
8// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
9// MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHORS 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 tag as Self
48 }
49}
50
51impl From<Tag> for u8 {
52 fn from(tag: Tag) -> Self {
53 tag as Self
54 } // XXX: narrowing conversion.
55}
56
57pub fn expect_tag_and_get_value<'a>(
58 input: &mut untrusted::Reader<'a>,
59 tag: Tag,
60) -> Result<untrusted::Input<'a>, error::Unspecified> {
61 let (actual_tag: u8, inner: Input<'_>) = read_tag_and_get_value(input)?;
62 if usize::from(tag) != usize::from(actual_tag) {
63 return Err(error::Unspecified);
64 }
65 Ok(inner)
66}
67
68pub fn read_tag_and_get_value<'a>(
69 input: &mut untrusted::Reader<'a>,
70) -> Result<(u8, untrusted::Input<'a>), error::Unspecified> {
71 let tag = input.read_byte()?;
72 if (tag & 0x1F) == 0x1F {
73 return Err(error::Unspecified); // High tag number form is not allowed.
74 }
75
76 // If the high order bit of the first byte is set to zero then the length
77 // is encoded in the seven remaining bits of that byte. Otherwise, those
78 // seven bits represent the number of bytes used to encode the length.
79 let length = match input.read_byte()? {
80 n if (n & 0x80) == 0 => usize::from(n),
81 0x81 => {
82 let second_byte = input.read_byte()?;
83 if second_byte < 128 {
84 return Err(error::Unspecified); // Not the canonical encoding.
85 }
86 usize::from(second_byte)
87 }
88 0x82 => {
89 let second_byte = usize::from(input.read_byte()?);
90 let third_byte = usize::from(input.read_byte()?);
91 let combined = (second_byte << 8) | third_byte;
92 if combined < 256 {
93 return Err(error::Unspecified); // Not the canonical encoding.
94 }
95 combined
96 }
97 _ => {
98 return Err(error::Unspecified); // We don't support longer lengths.
99 }
100 };
101
102 let inner = input.read_bytes(length)?;
103 Ok((tag, inner))
104}
105
106#[inline]
107pub fn bit_string_with_no_unused_bits<'a>(
108 input: &mut untrusted::Reader<'a>,
109) -> Result<untrusted::Input<'a>, error::Unspecified> {
110 bit_string_tagged_with_no_unused_bits(Tag::BitString, input)
111}
112
113pub(crate) fn bit_string_tagged_with_no_unused_bits<'a>(
114 tag: Tag,
115 input: &mut untrusted::Reader<'a>,
116) -> Result<untrusted::Input<'a>, error::Unspecified> {
117 nested(input, tag, error:error::Unspecified, |value: &mut Reader<'_>| {
118 let unused_bits_at_end: u8 = value.read_byte().map_err(|_| error::Unspecified)?;
119 if unused_bits_at_end != 0 {
120 return Err(error::Unspecified);
121 }
122 Ok(value.read_bytes_to_end())
123 })
124}
125
126// TODO: investigate taking decoder as a reference to reduce generated code
127// size.
128pub fn nested<'a, F, R, E: Copy>(
129 input: &mut untrusted::Reader<'a>,
130 tag: Tag,
131 error: E,
132 decoder: F,
133) -> Result<R, E>
134where
135 F: FnOnce(&mut untrusted::Reader<'a>) -> Result<R, E>,
136{
137 let inner: Input<'_> = expect_tag_and_get_value(input, tag).map_err(|_| error)?;
138 inner.read_all(incomplete_read:error, read:decoder)
139}
140
141pub(crate) fn nonnegative_integer<'a>(
142 input: &mut untrusted::Reader<'a>,
143) -> Result<untrusted::Input<'a>, error::Unspecified> {
144 let value: Input<'_> = expect_tag_and_get_value(input, Tag::Integer)?;
145 match value
146 .as_slice_less_safe()
147 .split_first()
148 .ok_or(err:error::Unspecified)?
149 {
150 // Zero or leading zero.
151 (0, rest: &[u8]) => {
152 match rest.first() {
153 // Zero.
154 None => Ok(value),
155 // Necessary leading zero.
156 Some(&second: u8) if second & 0x80 == 0x80 => Ok(untrusted::Input::from(bytes:rest)),
157 // Unnecessary leading zero.
158 _ => Err(error::Unspecified),
159 }
160 }
161 // Positive value with no leading zero.
162 (first: &u8, _) if first & 0x80 == 0 => Ok(value),
163 // Negative value.
164 (_, _) => Err(error::Unspecified),
165 }
166}
167
168/// Parse as integer with a value in the in the range [0, 255], returning its
169/// numeric value. This is typically used for parsing version numbers.
170#[inline]
171pub fn small_nonnegative_integer(input: &mut untrusted::Reader) -> Result<u8, error::Unspecified> {
172 let value: Input<'_> = nonnegative_integer(input)?;
173 match *value.as_slice_less_safe() {
174 [b: u8] => Ok(b),
175 _ => Err(error::Unspecified),
176 }
177}
178
179/// Parses a positive DER integer, returning the big-endian-encoded value,
180/// sans any leading zero byte.
181pub fn positive_integer<'a>(
182 input: &mut untrusted::Reader<'a>,
183) -> Result<Positive<'a>, error::Unspecified> {
184 let value: Input<'_> = nonnegative_integer(input)?;
185 Positive::from_be_bytes(input:value)
186}
187
188#[cfg(test)]
189mod tests {
190 use super::*;
191 use crate::error;
192
193 fn with_i<'a, F, R>(value: &'a [u8], f: F) -> Result<R, error::Unspecified>
194 where
195 F: FnOnce(&mut untrusted::Reader<'a>) -> Result<R, error::Unspecified>,
196 {
197 untrusted::Input::from(value).read_all(error::Unspecified, f)
198 }
199
200 static ZERO_INTEGER: &[u8] = &[0x02, 0x01, 0x00];
201
202 static GOOD_POSITIVE_INTEGERS_SMALL: &[(&[u8], u8)] = &[
203 (&[0x02, 0x01, 0x01], 0x01),
204 (&[0x02, 0x01, 0x02], 0x02),
205 (&[0x02, 0x01, 0x7e], 0x7e),
206 (&[0x02, 0x01, 0x7f], 0x7f),
207 // Values that need to have an 0x00 prefix to disambiguate them from
208 // them from negative values.
209 (&[0x02, 0x02, 0x00, 0x80], 0x80),
210 (&[0x02, 0x02, 0x00, 0x81], 0x81),
211 (&[0x02, 0x02, 0x00, 0xfe], 0xfe),
212 (&[0x02, 0x02, 0x00, 0xff], 0xff),
213 ];
214
215 static GOOD_POSITIVE_INTEGERS_LARGE: &[(&[u8], &[u8])] = &[
216 (&[0x02, 0x02, 0x01, 0x00], &[0x01, 0x00]),
217 (&[0x02, 0x02, 0x02, 0x01], &[0x02, 0x01]),
218 (&[0x02, 0x02, 0x7e, 0xfe], &[0x7e, 0xfe]),
219 (&[0x02, 0x02, 0x7f, 0xff], &[0x7f, 0xff]),
220 // Values that need to have an 0x00 prefix to disambiguate them from
221 // them from negative values.
222 (&[0x02, 0x03, 0x00, 0x80, 0x00], &[0x80, 0x00]),
223 (&[0x02, 0x03, 0x00, 0x81, 0x01], &[0x81, 0x01]),
224 (&[0x02, 0x03, 0x00, 0xfe, 0xfe], &[0xfe, 0xfe]),
225 (&[0x02, 0x03, 0x00, 0xff, 0xff], &[0xff, 0xff]),
226 ];
227
228 static BAD_NONNEGATIVE_INTEGERS: &[&[u8]] = &[
229 &[], // At end of input
230 &[0x02], // Tag only
231 &[0x02, 0x00], // Empty value
232 // Length mismatch
233 &[0x02, 0x00, 0x01],
234 &[0x02, 0x01],
235 // Would be valid if leading zero is ignored when comparing length.
236 &[0x02, 0x01, 0x00, 0x01],
237 &[0x02, 0x01, 0x01, 0x00], // Would be valid if last byte is ignored.
238 &[0x02, 0x02, 0x01],
239 // Values that are missing a necessary leading 0x00
240 &[0x02, 0x01, 0x80],
241 &[0x02, 0x01, 0x81],
242 &[0x02, 0x01, 0xfe],
243 &[0x02, 0x01, 0xff],
244 // Values that have an unnecessary leading 0x00
245 &[0x02, 0x02, 0x00, 0x00],
246 &[0x02, 0x02, 0x00, 0x01],
247 &[0x02, 0x02, 0x00, 0x02],
248 &[0x02, 0x02, 0x00, 0x7e],
249 &[0x02, 0x02, 0x00, 0x7f],
250 ];
251
252 #[test]
253 fn test_small_nonnegative_integer() {
254 let zero = (ZERO_INTEGER, 0x00);
255 for &(test_in, test_out) in
256 core::iter::once(&zero).chain(GOOD_POSITIVE_INTEGERS_SMALL.iter())
257 {
258 let result = with_i(test_in, |input| {
259 assert_eq!(small_nonnegative_integer(input)?, test_out);
260 Ok(())
261 });
262 assert_eq!(result, Ok(()));
263 }
264 for &test_in in BAD_NONNEGATIVE_INTEGERS
265 .iter()
266 .chain(GOOD_POSITIVE_INTEGERS_LARGE.iter().map(|(input, _)| input))
267 {
268 let result = with_i(test_in, small_nonnegative_integer);
269 assert_eq!(result, Err(error::Unspecified));
270 }
271 }
272
273 #[test]
274 fn test_positive_integer() {
275 for (test_in, test_out) in GOOD_POSITIVE_INTEGERS_SMALL
276 .iter()
277 .map(|(test_in, test_out)| (*test_in, core::slice::from_ref(test_out)))
278 .chain(GOOD_POSITIVE_INTEGERS_LARGE.iter().copied())
279 {
280 let result = with_i(test_in, |input| {
281 assert_eq!(
282 positive_integer(input)?.big_endian_without_leading_zero(),
283 test_out
284 );
285 Ok(())
286 });
287 assert_eq!(result, Ok(()))
288 }
289 for &test_in in core::iter::once(&ZERO_INTEGER).chain(BAD_NONNEGATIVE_INTEGERS.iter()) {
290 let result = with_i(test_in, positive_integer);
291 assert!(matches!(result, Err(error::Unspecified)));
292 }
293 }
294}
295