fix(vc): read Multibase base64url Bitstring Status List encodedLists - #235
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Bitstring Status List v1.0 defines encodedList as the Multibase base64url (u prefix, no padding) form of the GZIP-compressed bitstring. isRevoked handed it straight to BitBuffer.fromBitstring, which expects plain padded base64, so a list from a conformant issuer, including the example in the specification, failed as an unreadable encodedList and the status check could not complete. A u-prefixed list is now checked against the base64url alphabet and rewritten into the base64 bit-buffers reads; its inflate already accepts GZIP. Lists without the prefix are read as before, and plain base64 of a GZIP or zlib stream never starts with u, so the two forms cannot be confused.
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Walkthrough
ChangesBitstring encodedList decoding
Priority: ⬇️ Low Estimated code review effort: 2 (Simple) | ~10 minutes Change: Bug fix · Severity of issue fixed: Low Suggested reviewers: Merge Risk: 🔵 Low · up to Malformed status lists can be accepted as valid. Add the length check before merging, or explicitly accept this bounded validation gap. Security Architecture ReviewSecurity architecture risk: 🔵 Low · up to Conforming status lists can now be read during revocation checks. The existing proof, issuer, and list-identity checks still precede decoding, and unreadable lists still prevent verification. No bypass was identified, though coverage of downstream uses is incomplete. Retained concerns Security review detailsSecurity Blast Radius
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Inline comments:
Review comments at @packages/vc/src/verification/is-revoked.ts:
- Around line 49-77: Update decodeEncodedList to reject Base64URL payloads whose
length is 1 modulo 4, alongside the existing character validation, before
padding and decoding; preserve the existing error for invalid Multibase input.
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.changeset/bitstring-multibase-encoded-list.mdpackages/vc/src/verification/is-revoked.test.tspackages/vc/src/verification/is-revoked.ts
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A base64url string whose length is 1 modulo 4 cannot encode any byte string, but base64-js drops the trailing character and decodes the rest, so a malformed list could be read as the list before it. Treat such a list as unreadable.
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What
Bitstring Status List v1.0, Section 2.2 defines
encodedListas "a Multibase-encoded base64url (with no padding) representation of the GZIP-compressed bitstring".isRevokedpassed it straight toBitBuffer.fromBitstring, which expects plain, padded base64. A list from a conformant issuer, including the example in the specification (uH4sIAAAAAAAAA-3BMQEAAADCoPVPbQwfoAAAAAAAAAAAAAAAAAAAAIC3AYbSVKsAQAAA), fails withInvalid string. Length must be a multiple of 4and surfaces as an unreadableencodedList, so the credential's status cannot be determined.Change
A
u-prefixed list is checked against the base64url alphabet and rewritten into the padded base64 thatbit-buffersreads; its inflate already handles GZIP. Lists without the prefix are read exactly as before. Plain base64 of a GZIP or zlib stream never starts withu(that needs a first byte of 0xB8 to 0xBB, which is neither a GZIP magic byte nor a valid zlib header), so the two forms cannot be confused. The existingmaxEncodedListBytescap still applies before decoding.Tests
u+ base64url) reads as revoked.encodedListreads as not revoked.u-prefixed list that is not base64url still fails closed as unreadable.The first two fail on main.
pnpm run buildandpnpm run checkpass locally.Possible follow-up, not in this PR:
examples/issuerstill issues lists in the zlib + base64 form.AI disclosure: I used Claude to help with analysis, code and tests, and reviewed all changes myself.
Summary by CodeRabbit
u-prefixedencodedListvalue. Lists without the prefix continue to be read as before, and malformed values return an unreadable-list error.