der/asn1/integer/
uint.rs

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1//! Unsigned integer decoders/encoders.
2
3use crate::{Encoder, Length, Result, Tag};
4
5/// Decode an unsigned integer into a big endian byte slice with all leading
6/// zeroes removed.
7///
8/// Returns a byte array of the requested size containing a big endian integer.
9pub(super) fn decode_to_slice(bytes: &[u8]) -> Result<&[u8]> {
10    // The `INTEGER` type always encodes a signed value, so for unsigned
11    // values the leading `0x00` byte may need to be removed.
12    //
13    // We also disallow a leading byte which would overflow a signed ASN.1
14    // integer (since we're decoding an unsigned integer).
15    // We expect all such cases to have a leading `0x00` byte.
16    match bytes {
17        [] => Err(Tag::Integer.non_canonical_error()),
18        [0] => Ok(bytes),
19        [0, byte, ..] if *byte < 0x80 => Err(Tag::Integer.non_canonical_error()),
20        [0, rest @ ..] => Ok(rest),
21        [byte, ..] if *byte >= 0x80 => Err(Tag::Integer.value_error()),
22        _ => Ok(bytes),
23    }
24}
25
26/// Decode an unsigned integer into a byte array of the requested size
27/// containing a big endian integer.
28pub(super) fn decode_to_array<const N: usize>(bytes: &[u8]) -> Result<[u8; N]> {
29    let input = decode_to_slice(bytes)?;
30
31    // Input has leading zeroes removed, so we need to add them back
32    let mut output = [0u8; N];
33    output[N.saturating_sub(input.len())..].copy_from_slice(input);
34    Ok(output)
35}
36
37/// Encode the given big endian bytes representing an integer as ASN.1 DER.
38pub(super) fn encode_bytes(encoder: &mut Encoder<'_>, bytes: &[u8]) -> Result<()> {
39    let bytes = strip_leading_zeroes(bytes);
40
41    if needs_leading_zero(bytes) {
42        encoder.byte(0)?;
43    }
44
45    encoder.bytes(bytes)
46}
47
48/// Get the encoded length for the given unsigned integer serialized as bytes.
49#[inline]
50pub(super) fn encoded_len(bytes: &[u8]) -> Result<Length> {
51    let bytes = strip_leading_zeroes(bytes);
52    Length::try_from(bytes.len())? + needs_leading_zero(bytes) as u8
53}
54
55/// Strip the leading zeroes from the given byte slice
56pub(super) fn strip_leading_zeroes(mut bytes: &[u8]) -> &[u8] {
57    while let Some((byte, rest)) = bytes.split_first() {
58        if *byte == 0 && !rest.is_empty() {
59            bytes = rest;
60        } else {
61            break;
62        }
63    }
64
65    bytes
66}
67
68/// Does the given integer need a leading zero?
69fn needs_leading_zero(bytes: &[u8]) -> bool {
70    matches!(bytes.get(0), Some(byte) if *byte >= 0x80)
71}
der/asn1/integer/uint.rs

der/asn1/integer/
uint.rs
