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der: order UTCTime in SET OF by its encoding - #2448
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tarcieri merged 2 commits intoOct 5, 2026
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`UtcTime` used its chronological `Ord` as `ValueOrd` (`OrdIsValueOrd`).
X.690 11.6 orders `SET OF` components by their encodings, and a UTCTime
encodes the year as two digits (RFC 5280: 50..99 = 19xx, 00..49 = 20xx),
so the two orders disagree across 2000:
1999-12-31 23:59:59 -> "991231235959Z"
2000-01-01 00:00:00 -> "000101000000Z" (sorts first in DER)
`SetOfVec<UtcTime>` therefore encodes non-DER output for such sets, and
`SetOf`/`SetOfRef` reject the DER encoding.
Implement `ValueOrd` for `UtcTime` by comparing the encoded value. `Ord`
stays chronological.
dishmaker
reviewed
Oct 2, 2026
tarcieri
reviewed
Oct 5, 2026
Comment on lines
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| // Every field is encoded as two decimal digits, so comparing the fields in order is | ||
| // comparing the encodings. | ||
| let fields = |t: &Self| { | ||
| let dt = &t.0; | ||
| ( | ||
| dt.year() % 100, | ||
| dt.month(), | ||
| dt.day(), | ||
| dt.hour(), | ||
| dt.minutes(), | ||
| dt.seconds(), | ||
| ) | ||
| }; | ||
| Ok(fields(self).cmp(&fields(other))) |
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This seems like a little bit weird way of implementing this (i.e. using an anonymous function) versus just writing out the comparisons, but the fix seems correct so I'll go ahead and merge it
tarcieri
approved these changes
Oct 5, 2026
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UtcTimeuses its chronologicalOrdasValueOrd(impl OrdIsValueOrd for UtcTime). X.690 11.6 orders the components of a DERSET OFby their encodings. A UTCTime encodes the year as two digits: under RFC 5280,50..99is 19xx and00..49is 20xx. So the two orders disagree across 2000:SetOfVec<UtcTime>therefore encodes such a set out of DER order, andSetOf/SetOfRefreject the correctly ordered encoding.This PR implements
ValueOrdforUtcTimeby comparing the encodedYYMMDDHHMMSSZvalue.Ordstays chronological. No otherOrdIsValueOrdtype has this mismatch:GeneralizedTime's four-digit year sorts the same in both orders, and every pair ofObjectIdentifier,Int/Uint, string,BitStringandOctetStringvalues checked throughder_cmpagrees with octet order.Tests:
utc_time::tests::value_ord_is_encoding_order:value_cmp/der_cmpput 2000 before 1999, andOrdstill puts 1999 first.der/tests/set_of.rsutctime_order: aSetOfVec<UtcTime>holding both dates encodes 2000 first. It fails on master.This is independent of the
SET OFtag-order fix (der: order SET OF components by their encoded octets): the two touch different code and merge without conflict.This PR was produced by AI agents (Claude) during differential fuzzing of
der/x509-cert. It was found by checking everyOrdIsValueOrdtype'sder_cmpagainst the byte order of its encodings.