README.md

metadata

license: cc0-1.0
pretty_name: Common Crawl document-digest bloom filter
tags:
  - bloom-filter
  - file-hashes

Common Crawl document-digest bloom filter

Membership filter over payload sha1 digests of document-type captures (PDF ~74%, DOC/XLS/PPT/EPUB and similar) from one Common Crawl crawl's URL index — the ~1% of CC that isn't HTML. CC digests are SHA-1 of the (possibly truncated pre-2025) WARC payload; for static documents this equals the file's raw sha1.

• 30,951,194 sha1 keys (UPPERCASE hex), p = 1e-4, 71 MiB
• Source: CC-MAIN index content_digest column, filtered by MIME (crawl data © Common Crawl, generously public; this digest compilation CC0)
• One crawl only — a document must have been live and crawled that month to appear; more crawls widen coverage

Rebuild

cc_extract_job.py in this repo streams one crawl's CDXJ index (~1 h locally, $0), cc_digests_to_hex.py converts the base32 digests to hex, ./dcso_bloom_build.py cc.sha1.bloom sha1 builds the filter.

Format

DCSO bloom filter format (github.com/DCSO/bloom), the same format CIRCL publishes hashlookup in: 48-byte little-endian u64 header (version, n, p, k, m, N) followed by the bit array. Keys are hex digest strings — UPPERCASE for sha1, lowercase for sha256 (the hashlookup convention). Any DCSO-compatible reader works.

Membership answers are probabilistic: p = 1e-4 false-positive rate, no false negatives. Confirm anything important against the source.