blob: 457e350af67ba95b79b45233ce8ee6a20c51190b [file] [log] [blame]
// Copyright 2015 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.
//! Building blocks for parsing DER-encoded ASN.1 structures.
//!
//! This module contains the foundational parts of an ASN.1 DER parser.
use super::Positive;
use crate::error;
use untrusted;
pub const CONSTRUCTED: u8 = 1 << 5;
pub const CONTEXT_SPECIFIC: u8 = 2 << 6;
#[derive(Clone, Copy, PartialEq)]
#[repr(u8)]
pub enum Tag {
Boolean = 0x01,
Integer = 0x02,
BitString = 0x03,
OctetString = 0x04,
Null = 0x05,
OID = 0x06,
Sequence = CONSTRUCTED | 0x10, // 0x30
UTCTime = 0x17,
GeneralizedTime = 0x18,
ContextSpecificConstructed0 = CONTEXT_SPECIFIC | CONSTRUCTED | 0,
ContextSpecificConstructed1 = CONTEXT_SPECIFIC | CONSTRUCTED | 1,
ContextSpecificConstructed3 = CONTEXT_SPECIFIC | CONSTRUCTED | 3,
}
impl From<Tag> for usize {
fn from(tag: Tag) -> Self { tag as usize }
}
pub fn expect_tag_and_get_value<'a>(
input: &mut untrusted::Reader<'a>, tag: Tag,
) -> Result<untrusted::Input<'a>, error::Unspecified> {
let (actual_tag, inner) = read_tag_and_get_value(input)?;
if usize::from(tag) != usize::from(actual_tag) {
return Err(error::Unspecified);
}
Ok(inner)
}
pub fn read_tag_and_get_value<'a>(
input: &mut untrusted::Reader<'a>,
) -> Result<(u8, untrusted::Input<'a>), error::Unspecified> {
let tag = input.read_byte()?;
if (tag & 0x1F) == 0x1F {
return Err(error::Unspecified); // High tag number form is not allowed.
}
// If the high order bit of the first byte is set to zero then the length
// is encoded in the seven remaining bits of that byte. Otherwise, those
// seven bits represent the number of bytes used to encode the length.
let length = match input.read_byte()? {
n if (n & 0x80) == 0 => usize::from(n),
0x81 => {
let second_byte = input.read_byte()?;
if second_byte < 128 {
return Err(error::Unspecified); // Not the canonical encoding.
}
usize::from(second_byte)
},
0x82 => {
let second_byte = usize::from(input.read_byte()?);
let third_byte = usize::from(input.read_byte()?);
let combined = (second_byte << 8) | third_byte;
if combined < 256 {
return Err(error::Unspecified); // Not the canonical encoding.
}
combined
},
_ => {
return Err(error::Unspecified); // We don't support longer lengths.
},
};
let inner = input.skip_and_get_input(length)?;
Ok((tag, inner))
}
pub fn bit_string_with_no_unused_bits<'a>(
input: &mut untrusted::Reader<'a>,
) -> Result<untrusted::Input<'a>, error::Unspecified> {
nested(input, Tag::BitString, error::Unspecified, |value| {
let unused_bits_at_end = value.read_byte().map_err(|_| error::Unspecified)?;
if unused_bits_at_end != 0 {
return Err(error::Unspecified);
}
Ok(value.skip_to_end())
})
}
// TODO: investigate taking decoder as a reference to reduce generated code
// size.
pub fn nested<'a, F, R, E: Copy>(
input: &mut untrusted::Reader<'a>, tag: Tag, error: E, decoder: F,
) -> Result<R, E>
where
F: FnOnce(&mut untrusted::Reader<'a>) -> Result<R, E>,
{
let inner = expect_tag_and_get_value(input, tag).map_err(|_| error)?;
inner.read_all(error, decoder)
}
fn nonnegative_integer<'a>(
input: &mut untrusted::Reader<'a>, min_value: u8,
) -> Result<untrusted::Input<'a>, error::Unspecified> {
// Verify that |input|, which has had any leading zero stripped off, is the
// encoding of a value of at least |min_value|.
fn check_minimum(input: untrusted::Input, min_value: u8) -> Result<(), error::Unspecified> {
input.read_all(error::Unspecified, |input| {
let first_byte = input.read_byte()?;
if input.at_end() && first_byte < min_value {
return Err(error::Unspecified);
}
let _ = input.skip_to_end();
Ok(())
})
}
let value = expect_tag_and_get_value(input, Tag::Integer)?;
value.read_all(error::Unspecified, |input| {
// Empty encodings are not allowed.
let first_byte = input.read_byte()?;
if first_byte == 0 {
if input.at_end() {
// |value| is the legal encoding of zero.
if min_value > 0 {
return Err(error::Unspecified);
}
return Ok(value);
}
let r = input.skip_to_end();
r.read_all(error::Unspecified, |input| {
let second_byte = input.read_byte()?;
if (second_byte & 0x80) == 0 {
// A leading zero is only allowed when the value's high bit
// is set.
return Err(error::Unspecified);
}
let _ = input.skip_to_end();
Ok(())
})?;
check_minimum(r, min_value)?;
return Ok(r);
}
// Negative values are not allowed.
if (first_byte & 0x80) != 0 {
return Err(error::Unspecified);
}
let _ = input.skip_to_end();
check_minimum(value, min_value)?;
Ok(value)
})
}
/// Parse as integer with a value in the in the range [0, 255], returning its
/// numeric value. This is typically used for parsing version numbers.
#[inline]
pub fn small_nonnegative_integer(input: &mut untrusted::Reader) -> Result<u8, error::Unspecified> {
let value = nonnegative_integer(input, 0)?;
value.read_all(error::Unspecified, |input| {
let r = input.read_byte()?;
Ok(r)
})
}
/// Parses a positive DER integer, returning the big-endian-encoded value,
/// sans any leading zero byte.
pub fn positive_integer<'a>(
input: &mut untrusted::Reader<'a>,
) -> Result<Positive<'a>, error::Unspecified> {
Ok(Positive(nonnegative_integer(input, 1)?))
}
#[cfg(test)]
mod tests {
use super::*;
use crate::error;
use untrusted;
fn with_good_i<F, R>(value: &[u8], f: F)
where
F: FnOnce(&mut untrusted::Reader) -> Result<R, error::Unspecified>,
{
let r = untrusted::Input::from(value).read_all(error::Unspecified, f);
assert!(r.is_ok());
}
fn with_bad_i<F, R>(value: &[u8], f: F)
where
F: FnOnce(&mut untrusted::Reader) -> Result<R, error::Unspecified>,
{
let r = untrusted::Input::from(value).read_all(error::Unspecified, f);
assert!(r.is_err());
}
static ZERO_INTEGER: &'static [u8] = &[0x02, 0x01, 0x00];
static GOOD_POSITIVE_INTEGERS: &'static [(&'static [u8], u8)] = &[
(&[0x02, 0x01, 0x01], 0x01),
(&[0x02, 0x01, 0x02], 0x02),
(&[0x02, 0x01, 0x7e], 0x7e),
(&[0x02, 0x01, 0x7f], 0x7f),
// Values that need to have an 0x00 prefix to disambiguate them from
// them from negative values.
(&[0x02, 0x02, 0x00, 0x80], 0x80),
(&[0x02, 0x02, 0x00, 0x81], 0x81),
(&[0x02, 0x02, 0x00, 0xfe], 0xfe),
(&[0x02, 0x02, 0x00, 0xff], 0xff),
];
static BAD_NONNEGATIVE_INTEGERS: &'static [&'static [u8]] = &[
&[], // At end of input
&[0x02], // Tag only
&[0x02, 0x00], // Empty value
// Length mismatch
&[0x02, 0x00, 0x01],
&[0x02, 0x01],
&[0x02, 0x01, 0x00, 0x01],
&[0x02, 0x01, 0x01, 0x00], // Would be valid if last byte is ignored.
&[0x02, 0x02, 0x01],
// Negative values
&[0x02, 0x01, 0x80],
&[0x02, 0x01, 0xfe],
&[0x02, 0x01, 0xff],
// Values that have an unnecessary leading 0x00
&[0x02, 0x02, 0x00, 0x00],
&[0x02, 0x02, 0x00, 0x01],
&[0x02, 0x02, 0x00, 0x02],
&[0x02, 0x02, 0x00, 0x7e],
&[0x02, 0x02, 0x00, 0x7f],
];
#[test]
fn test_small_nonnegative_integer() {
with_good_i(ZERO_INTEGER, |input| {
assert_eq!(small_nonnegative_integer(input)?, 0x00);
Ok(())
});
for &(test_in, test_out) in GOOD_POSITIVE_INTEGERS.iter() {
with_good_i(test_in, |input| {
assert_eq!(small_nonnegative_integer(input)?, test_out);
Ok(())
});
}
for &test_in in BAD_NONNEGATIVE_INTEGERS.iter() {
with_bad_i(test_in, |input| {
let _ = small_nonnegative_integer(input)?;
Ok(())
});
}
}
#[test]
fn test_positive_integer() {
with_bad_i(ZERO_INTEGER, |input| {
let _ = positive_integer(input)?;
Ok(())
});
for &(test_in, test_out) in GOOD_POSITIVE_INTEGERS.iter() {
with_good_i(test_in, |input| {
let test_out = [test_out];
assert_eq!(
positive_integer(input)?.big_endian_without_leading_zero(),
untrusted::Input::from(&test_out[..])
);
Ok(())
});
}
for &test_in in BAD_NONNEGATIVE_INTEGERS.iter() {
with_bad_i(test_in, |input| {
let _ = positive_integer(input)?;
Ok(())
});
}
}
}