SafeStream-Redactor

Streaming PII & credential redaction for massive text files — constant O(1) memory, multi-tier detection (regex + validators + entropy + optional NER + contextual heuristics), fully customizable redaction.

Redact a 100 GB log file with the same memory footprint as a 1 KB one.

Unlike general PII engines (Presidio, scrubadub) it also detects credentials and secrets — AWS keys, GitHub/Slack/Stripe/Google/SendGrid/Twilio/npm tokens, JWTs, private-key blocks, and undocumented high-entropy secrets — in the same streaming pass.

Why?

Most PII tools load the whole document into memory. SafeStream-Redactor processes text in fixed-size chunks with an overlapping context window, so entities that straddle chunk boundaries are still caught — and memory use never grows with file size (proven by a test that redacts a generated 1 GB file under a 16 MB allocation cap).

Install

Three ways — pip, from source, or Docker:

# 1. pip (constant-memory core, zero third-party runtime deps)
pip install safestream-redactor

# optional spaCy-based PERSON/ORG/LOC detection:
pip install 'safestream-redactor[ner]'
python -m spacy download en_core_web_sm

# 2. from a clone (for development or the latest main)
git clone https://github.com/MounishSenisetty/SafeStream-Redactor
cd SafeStream-Redactor
pip install -e '.[dev]'

# 3. Docker — nothing to install locally; mount a directory and go
docker build -t safestream-redactor .
docker run --rm -v "$PWD":/data safestream-redactor \
    redact /data/input.txt -o /data/output.txt

# released multi-arch images (amd64/arm64, with SBOM + provenance) are on GHCR:
docker run --rm -v "$PWD":/data ghcr.io/mounishsenisetty/safestream-redactor \
    redact /data/input.txt -o /data/output.txt

Quickstart

CLI

# redact everything detectable, write to out.txt
safestream redact input.txt -o out.txt

# only emails + SSNs, custom replacement, plus a custom codename
safestream redact input.txt -o out.txt --types email,ssn --replace "***" --custom-word "ProjectX"

# mask all but the last 4 characters
safestream redact cards.csv -o masked.csv --mode mask --keep-last 4

# deterministic pseudonyms (same input -> same token), streaming from stdin
tail -f app.log | safestream redact - -o - --mode pseudonymize --hmac-key "$SECRET"

# redact a whole directory tree in parallel (RAM/CPU-aware worker count)
safestream redact ./logs -o ./logs_redacted --workers 8

# ...or split ONE big file across cores — output is byte-identical to the
# single-core pass (a seam cross-check guarantees no lost/duplicated text)
safestream redact huge.log -o huge_redacted.log --workers 8

# just list what would be redacted
safestream detect input.txt --json

# CI / pre-commit secret gate: non-zero exit if anything is found
safestream detect build.log --fail-on-detect

# per-type counts to stderr, plus a JSON run report for compliance filing
# (the report contains only type names, counts, and sizes — never matched text)
safestream redact input.txt -o out.txt --stats --report run.json

# non-UTF-8 source? decode it correctly (undecodable bytes are otherwise
# reported and warned about, since unscanned bytes are a coverage risk)
safestream redact legacy.log -o out.log --encoding latin-1

# generate a documented, validated starter policy to customise
safestream init-config -o policy.toml

While redacting, the CLI installs an offline network guard by default: any attempt to open a non-loopback connection through Python's socket layer raises an error. This is best-effort, defense-in-depth egress prevention for this process, its plugins, and its Python dependencies — not a hard boundary: native extensions issuing raw syscalls, a spawned subprocess, or another process on the machine are outside its reach. For a guaranteed boundary, also run with no network (docker run --network none ...) or a network namespace / seccomp policy. Pass --allow-network to disable the guard. See SECURITY.md for the full threat model.

Python API

from safestream_redactor import Redactor, RedactionPolicy, EntityType

redactor = Redactor()
redactor.redact("email bob@corp.io, ssn: 123-45-6789")
# 'email [REDACTED], ssn: [REDACTED]'

# detection only
for d in redactor.detect("card 4111 1111 1111 1111"):
    print(d.entity_type, d.confidence, d.text)

# per-type replacements
policy = RedactionPolicy(replacements={EntityType.EMAIL: "<EMAIL>"})
Redactor(policy=policy).redact("write to bob@corp.io")   # 'write to <EMAIL>'

# constant-memory file-to-file; the write is atomic (never a partial output)
# and the returned stats carry per-type counts — content-free audit evidence
stats = Redactor().redact_file("huge.log", "huge_redacted.log")
print(stats.summary())   # '3 detection(s): email=2, ssn=1'

# generator-based streaming (any iterable of text chunks)
with open("huge.log") as f:
    for clean_chunk in Redactor().redact_stream(iter(lambda: f.read(65536), "")):
        process(clean_chunk)

# parallel, RAM-aware redaction across a directory tree
from safestream_redactor.scheduler import redact_tree
redact_tree("logs/", "logs_redacted/", Redactor(), workers=8)

# split a single large file across cores; byte-identical to the sequential pass
Redactor().redact_file("huge.log", "huge_redacted.log", workers=8)

# enforce the offline guarantee around any block of code
from safestream_redactor import netguard
with netguard.enforced():
    Redactor().redact_file("huge.log", "huge_redacted.log")   # network calls now raise

Extending with plugins

Any installed package can add a detection tier by advertising an entry point — no fork required. SafeStream discovers and loads them automatically.

# in your plugin package's pyproject.toml
[project.entry-points."safestream_redactor.detectors"]
my_detector = "my_pkg.detectors:MyDetector"   # a Detector instance or zero-arg factory

A detector is anything with a name and detect(text) -> list[Detection] (the Detector protocol). Disable plugin loading with Redactor(load_plugins=False).

Policy files (TOML)

# policy.toml
[detection]
types = ["email", "ssn", "credit_card"]

[redaction]
mode = "replace"
replacement = "[GONE]"

[redaction.replacements]
email = "<EMAIL>"

[custom]
words = ["ProjectX"]

safestream redact input.txt -o out.txt --config policy.toml

A fuller, ready-to-use policy — NER enabled, plus custom patterns for passport / driver-licence / bank-account / routing / employee-ID / Slack-ID / DOB values — ships in examples/policy.toml. Generate a minimal starter with safestream init-config -o policy.toml.

Architecture

 chunks ──> [ rolling buffer + overlap window ] ──> redacted chunks
                     │
                     ▼
        ┌───────────────────────────┐
        │ Tier 1  deterministic     │  regex + validators (Luhn, SSN rules,
        │                           │  ipaddress parsing, ...) + credentials
        ├───────────────────────────┤
        │ Tier 2  statistical       │  Shannon-entropy scoring for bespoke,
        │                           │  undocumented high-entropy secrets
        ├───────────────────────────┤
        │ Tier 3  NER (optional)    │  spaCy PERSON / ORG / LOC
        ├───────────────────────────┤
        │ Tier 4  contextual        │  trigger words boost/suppress
        │                           │  confidence ("ssn:", "example", ...)
        └───────────────────────────┘
                     │
          confidence filter + overlap resolution
                     │
                     ▼
          redaction policy (replace / mask / pseudonymize / per-type)

  Scheduler: RAM/CPU-aware multiprocessing across files (safestream/scheduler.py).
  Parallel: one big file split into character-aligned ranges, output byte-identical
    to the sequential pass, seam cross-check falls back on disagreement (parallel.py).
  Offline guard: any non-loopback connection raises NetworkAccessError (netguard.py).
  Plugins: third-party tiers load from the 'safestream_redactor.detectors' entry point.

Each tier-1 pattern declares literal anchors every match must contain (AKIA, eyJ, @, ://, a digit, …); a cheap substring scan per window skips regexes that cannot match, so secret-sparse text runs ~25× faster with provably identical output (a differential test compares prefiltered and unfiltered detection).

The streaming engine keeps a rolling buffer of chunk_size + overlap characters. Only text at least overlap characters from the buffer's end is emitted each round; the tail is carried into the next round so any entity up to overlap characters long (default 4 KB) is always seen whole at least once, even when a chunk boundary cuts straight through it. An emit boundary that would split a detection retreats to the detection's start. Already-emitted text is kept (up to overlap chars) as read-only left context so the contextual tier scores identically to whole-text mode.

Detected entity types:

• PII: email, phone, credit_card (Luhn-validated), ssn, ipv4, ipv6, plus person / org / loc with the NER extra.
• Credentials & secrets: aws_key, aws_secret (the 40-char secret behind an aws … secret … key label), github_token, slack_token, slack_webhook, stripe_key, google_api_key, sendgrid_key, twilio_key, npm_token, openai_key, anthropic_key, jwt, private_key, url_credentials (passwords embedded in connection strings — only the password is redacted, so postgres://svc:hunter2@db/app becomes postgres://svc:[REDACTED]@db/app), api_key (generic key = value assignments), and secret (undocumented high-entropy strings, on by default — disable with --no-entropy).
• custom for user-supplied words and regexes.

Evaluation

Read this before quoting any number below. The corpora these numbers come from are synthetic and self-generated: the gold positives are emitted in the same canonical formats the detector targets, so a near-perfect score on them measures format coverage and false-positive resistance, not real-world recall. They are a regression fixture, not an accuracy claim, and a self-generated benchmark is not evidence of accuracy on your data. For a defensible accuracy number, run benchmarks/evaluate.py against an independent labeled corpus you control (see benchmarks/README.md — the Presidio research dataset, CoNLL, and the n2c2 de-identification set are the recommended targets). Expect recall on free-form prose (names, addresses) to be substantially lower than on structured PII unless the [ner] extra is enabled.

Format coverage & false-positive resistance (synthetic). On the adversarial corpus (1 MB of noisy log/JSON/CSV/SQL dense with hard negatives — order numbers, ISO timestamps, UUIDs, git hashes, invalid-area SSNs, 5-octet version strings; reproduce with benchmarks/generate_hard_dataset.py then benchmarks/run_benchmark.py):

* Recall here is against self-generated positives and is not a real-world recall figure — see the note above. The meaningful, non-circular result in this table is precision under distractors: SafeStream holds 0.999 while Presidio's phone recognizer emits thousands of false positives (P=0.649). Presidio was run via its pattern recognizers; its spaCy NER tier is a separate, model-dependent path that will out-recall SafeStream's regex core on prose unless you enable [ner].

Throughput is a known limitation, not a strength. ~3 MB/s single-core means a 100 GB file takes hours; compiled scanners (gitleaks, ripgrep-class) are 100–1000× faster. The value here is constant memory and credential coverage, not raw speed. A single large file can now be split across cores with --workers N / redact_file(..., workers=N) — measured ~3.7× on 4 cores, with byte-identical output to the single-core pass (a seam cross-check falls back to sequential rather than risk differing output). That narrows but does not close the gap to compiled scanners; a Vectorscan/re2 backend for the remaining constant factor stays on the roadmap.

Credentials & secrets — the genuinely differentiating capability. On a corpus of AWS keys, GitHub/Slack/Stripe/Google/SendGrid/npm tokens, JWTs, and a random high-entropy secret, Presidio ships no recognizers and detects 0/9; SafeStream detects 9/9. This is a capability difference (Presidio has no credential recognizers at all), not a tuned accuracy comparison.

Detection accuracy & limitations

100% recall and 100% precision together are not achievable for free-text PII, by anyone. Names, street addresses, bank account numbers, and employee IDs have no distinctive form — a bank account number is indistinguishable from any other run of digits, and "April" is both a name and a month. Any detector faces a precision/recall tradeoff: catch every possible name and you also redact ordinary words; redact only unambiguous matches and you miss the rest. SafeStream is tuned to favour precision on structured PII and credentials, with names and format-less identifiers handled by the opt-in levers below. Treat it as high-recall for credentials and structured PII, and best-effort for free prose — not as a guarantee of catching everything.

Why a file labelled "TEST" under-detects. The contextual tier deliberately subtracts confidence from any value sitting next to test, sample, example, dummy, fake, placeholder, or lorem (see detectors/contextual.py). This keeps documentation snippets and fixture data from being redacted. The side effect is that a file saturated with those marker words — e.g. a sample log full of TEST DATA, fake, example, TestPass — has most of its detections pushed below the default 0.5 threshold and left untouched. That is working as designed: on real data (without the marker words) recall is substantially higher. If you want those suppressed values redacted anyway, lower min_confidence (below).

Three levers to raise recall, in increasing order of effort:

1. Lower min_confidence. The default is 0.5. Setting it to 0.35 (--min-confidence 0.35, or in a policy file) recovers most values the test/sample suppression demotes, at some cost to precision. Do this per-run on data you know is noisy — not globally on trusted prose.

2. Enable NER for names. Person / org / location names need the optional spaCy tier: pip install 'safestream-redactor[ner]' then python -m spacy download en_core_web_sm, and run with --ner (or use_ner = true in a policy). Without it, names are not detected at all.

3. Add custom patterns for format-less identifiers. Passport numbers, driver licences, bank/routing/account numbers, employee IDs, Slack user IDs, and dates of birth have no universal signature, so they need label-anchored regexes you supply. A ready-to-use policy covering all of these ships in examples/policy.toml:

   safestream detect input.txt --config examples/policy.toml
   

   It also enables NER and documents each lever inline. Custom patterns redact the whole match (including the label word) — the fail-safe outcome for DLP.

Development

git clone https://github.com/MounishSenisetty/SafeStream-Redactor
cd SafeStream-Redactor
pip install -e '.[dev]'
pytest                                   # fast suite (incl. property-based tests)
pytest --cov=safestream_redactor         # with the 95% coverage gate
SAFESTREAM_MEMTEST_MB=100 pytest -m memory -o addopts=''   # constant-memory proof
ruff check . && ruff format --check .       # lint + format
mypy                                        # strict type check

See CONTRIBUTING.md. Good first issues live in docs/good_first_issues.md and the issue tracker. The audited state of the codebase and the phased improvement plan are in docs/AUDIT.md and docs/ROADMAP.md; the security policy and threat model (what the offline guard does and does not cover) are in SECURITY.md.

License

MIT