> For clean Markdown of any page, append .md to the page URL.
> For a complete documentation index, see https://docs.adid.dev/llms.txt.
> For full documentation content, see https://docs.adid.dev/llms-full.txt.

# Bitstring Status List 2021

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**What it is.** The W3C [Bitstring Status List](https://www.w3.org/TR/vc-bitstring-status-list/) (the renamed successor of Status List 2021) bitstring approach. Each issuer maintains one or more "status list credentials" that themselves are VCs whose subject is a gzipped, base64-encoded bitstring. Revoked credentials are marked by setting bit `statusListIndex` to `1`.

**IDA's deviation from spec.** The on-chain `RevocationRegistry` (§11.4) is **complementary**, not replacement, to Status List 2021. IDA dual-anchors revocation: bit set in the bitstring (off-chain primary) AND `revokeCredential` event on chain (primary audit trail). This is intentional non-conformance with strict Status List 2021 because the on-chain anchor gives verifiers a tamper-evident timestamp without trusting the issuer's bitstring host.

**Source:** `docs/verifiable-credentials/revocation.md` ✅.