sether 0.1.1

Streaming PII redaction for AI applications. The hiding place for sensitive data flowing into LLMs. Secrets pack, SSE-aware streaming, audit events, drop-in middlewares for httpx / ASGI / WSGI / OpenAI / Anthropic.

Sether (Python)

Hide personal data from your AI before it reaches any LLM provider.

Named for the Hebrew sether (סֵתֶר), the hiding place. Psalm 32:7.

Your app → Sether redacts locally → LLM. The token vault stays in your infrastructure; restore_sync() swaps the originals back into the reply.

Sether is a streaming PII-redaction layer that sits between your application and any LLM API. It detects sensitive data (email, phone, SSN, credit card, IBAN, IP addresses, secrets, and labelled identity fields), swaps each match for a stable token before the request leaves your boundary, then restores the original values transparently in the response.

This is the Python port of @raeven-co/sether. Same detection engine, same token format, same chunk-boundary streaming safety, ported faithfully to Python with both synchronous and asynchronous streaming and drop-in integrations for httpx, ASGI (FastAPI / Starlette), WSGI (Flask), the OpenAI SDK, and the Anthropic SDK.

A product of Raeven Company LTD.

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Why this exists

If your application sends a customer's email, phone number, or any other PII to an LLM provider, that is a sub-processor disclosure under GDPR Article 28. Credit-card data pulls you into PCI DSS scope. Health identifiers trigger HIPAA. Sether stops the leak at the boundary: sensitive substrings become stable tokens before the bytes leave your process, and restore() swaps them back so your application code does not need to branch on redacted text.

This package does not phone home. Streams are not sent to Raeven. The vault stays in your process (or your own backing store if you implement Vault).

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Install

pip install sether

Requires Python 3.9+. The phone detector uses phonenumbers (installed automatically). Integration extras are optional:

pip install "sether[openai]"      # wrap_openai
pip install "sether[anthropic]"   # wrap_anthropic
pip install "sether[httpx]"       # wrap_httpx
pip install "sether[all]"         # all of the above

The ASGI and WSGI middlewares have no extra dependency.

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60-second quickstart

from sether import Sether

sether = Sether()

# Outgoing: redact before sending to the LLM.
safe = sether.redact_sync("my email is [e-mail]")
# -> "my email is <EMAIL_xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx>"

# Incoming: restore before showing the user.
back = sether.restore_sync(safe)
# -> "my email is [e-mail]"

The same Sether instance shares its vault between redaction and restoration, which is how the round-trip identity is preserved.

Streaming (sync and async)

sether = Sether()

# Synchronous: any iterable of text chunks.
def chunks():
    yield "Contact alice@"
    yield "example.com or call "
    yield "[phone]."

redacted = "".join(sether.redact_stream(chunks()))
restored = "".join(sether.restore_stream([redacted]))

# Asynchronous: any async iterable (e.g. an LLM token stream).
async def run(llm_stream):
    async for piece in sether.aredact_stream(llm_stream):
        await forward_to_model(piece)

The redact stream holds back safe_distance_bytes (default 256) at the tail of each chunk so a PII pattern crossing a chunk boundary is still detected when the next chunk arrives. A long whitespace-free value (a JWT, an API key) is held back up to max(safe_distance_bytes * 4, 8192) bytes so it is never emitted partially across a boundary. For values larger than that bound, raise safe_distance_bytes or use redact_sync on complete payloads. This round-trip identity is verified by property-based tests over 60 random chunk partitions.

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Detectors

By default Sether runs the basic pack. Pass an explicit list to narrow scope, or add the opt-in packs.

from sether import Sether, basic_detectors, secrets_detectors, identity_detectors

sether = Sether(detectors=[*basic_detectors, *secrets_detectors, *identity_detectors])

Basic pack (basic_detectors)

Detector	Type	Method
email_detector	EMAIL	RFC-5321-style regex. ASCII-only.
phone_detector	PHONE	phonenumbers (international format). For national-format numbers use create_phone_detector(default_country="US").
credit_card_detector	CC	Bounded regex + Luhn check.
ssn_detector	SSN	Regex + SSA invalid-prefix rules.
ipv4_detector	IPV4	Strict octet-bounded regex.
ipv6_detector	IPV6	Candidate regex + in-tree validator.
iban_detector	IBAN	Regex + mod-97 checksum.

Secrets pack (secrets_detectors)

aws_access_key_detector, openai_key_detector, anthropic_key_detector, github_pat_detector (classic + fine-grained), slack_token_detector, stripe_key_detector, jwt_detector, high_entropy_detector (Shannon entropy >= 3.5 bits/char).

Identity pack (identity_detectors, opt-in)

Label-anchored detection for names, dates of birth, passport numbers, and addresses. A value is redacted only when it appears with the label that introduces it (Name:, DOB:, Passport No:, Address:) or, for a few distinctive standalone shapes (a street line with a house number, a UK postcode), a structure strong enough to keep false positives low. Labels are recognised across many languages (Latin-script plus CJK, Cyrillic, Arabic), and value capture is Unicode-aware.

Free-text NER (unlabelled names, organisations, locations in running prose) is not covered here; that is the separate sether-ner roadmap item.

Custom detectors

Anything with a type string and a detect(text) method works:

import re
from sether import DetectorMatch

class OrderIdDetector:
    type = "ORDER_ID"
    _re = re.compile(r"\bORD-\d{8}\b")

    def detect(self, text):
        return [DetectorMatch(m.start(), m.end(), m.group(0)) for m in self._re.finditer(text)]

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Token vault

Tokens map back to originals through a vault. Sether ships an in-memory LRU vault (10,000 entries, 1-hour TTL by default). Implement the Vault protocol to change eviction, encrypt at rest, or namespace tokens per tenant.

from sether import Vault   # a runtime-checkable Protocol: set/get/has/delete/size/clear

class NamespacedVault:
    def __init__(self, prefix):
        self._store = {}
        self._prefix = prefix
    def set(self, token, value): self._store[self._prefix + token] = value
    def get(self, token): return self._store.get(self._prefix + token)
    def has(self, token): return (self._prefix + token) in self._store
    def delete(self, token): return self._store.pop(self._prefix + token, None) is not None
    def size(self): return len(self._store)
    def clear(self): self._store.clear()

sether = Sether(vault=NamespacedVault("tenant-42:"))

The Vault interface is synchronous: restore substitutes tokens as bytes flow through and cannot await a lookup per token. Front an async store (Redis, Postgres) with a synchronous in-process cache you hydrate before the restore pass, or keep the vault in-process.

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SSE / JSON-stream mode

OpenAI and Anthropic streaming responses come back as Server-Sent Events. The SSE-aware stream redacts payloads inside data: lines while preserving the data: / event: / id: / retry: framing and blank-line separators verbatim.

from sether import create_sse_redact_stream, basic_detectors, MemoryVault

vault = MemoryVault()
stream = create_sse_redact_stream(basic_detectors, vault)
out = stream.feed(sse_chunk) + stream.finish()
# or the iterator helpers: sse_redact_iter(chunks, detectors, vault)

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Drop-in integrations

from sether import Sether
sether = Sether()

httpx

import httpx
from sether import wrap_httpx

client = wrap_httpx(httpx.Client(), detectors=sether.detectors, vault=sether.vault)
r = client.post("https://api.example.com/v1/chat",
                json={"q": "email [e-mail]"})
# The request carried <EMAIL_...>; r.text has any tokens the server echoed restored.

Works on httpx.Client and httpx.AsyncClient. Binary bodies pass through untouched.

ASGI (FastAPI / Starlette)

from fastapi import FastAPI
from sether import SetherASGIMiddleware

app = FastAPI()
app.add_middleware(SetherASGIMiddleware, detectors=sether.detectors, vault=sether.vault)

WSGI (Flask)

from flask import Flask
from sether import SetherWSGIMiddleware

app = Flask(__name__)
app.wsgi_app = SetherWSGIMiddleware(app.wsgi_app, detectors=sether.detectors, vault=sether.vault)

OpenAI SDK

from openai import OpenAI
from sether import wrap_openai

client = wrap_openai(OpenAI(), detectors=sether.detectors, vault=sether.vault)
# Redacts messages out, restores choices back. Sync, async, and streaming clients.

Anthropic SDK

import anthropic
from sether import wrap_anthropic

client = wrap_anthropic(anthropic.Anthropic(), detectors=sether.detectors, vault=sether.vault)
# Redacts messages/system out, restores content blocks back.

The SDK wrappers are structurally typed. Sether never imports openai or anthropic; any object matching the chat.completions.create / messages.create shape works.

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Audit events

Each redaction can be described by a structured AuditEvent that maps to the regulation it satisfies (GDPR Art. 28, SOC 2 CC6.7, HIPAA, PCI DSS, and more, see DEFAULT_REGULATION_MAPPINGS). The original value is never carried in an event, only its length. The JSON wire shape matches the TypeScript package (camelCase keys) so events are interchangeable across both.

from sether import AuditEvent, ConsoleAuditSink, MemoryAuditSink

sink = ConsoleAuditSink()   # JSONL to stderr; MemoryAuditSink accumulates for tests
sink.write(AuditEvent(timestamp="...", detector="EMAIL", value_length=17, token="<EMAIL_x>"))

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Honest limitations

These match the TypeScript package's documented limits:

• Email detection is ASCII-only. IDN/Unicode local parts do not match.
• IPv6 ::1 (loopback) is not detected. The candidate regex requires 4+ chars. Loopback is not customer PII.
• Credit-card regex is permissive, then validated by Luhn. False positives in dense numeric content are possible.
• Names / DOB / passport / address are label-anchored, not free-text NER.
• Very large whitespace-free values split across chunk boundaries are held back only up to max(safe_distance_bytes * 4, 8192) bytes. Raise safe_distance_bytes or use redact_sync on complete payloads.

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Parity with the TypeScript package

This port reproduces the audited TypeScript engine 1:1: the same detector regexes (compiled with re.ASCII so \b / \d stay ASCII-only as in JS), the same Luhn / mod-97 / SSA validation, the same overlap resolution (longest match wins), the same <TYPE_uuid> token format, and the same safe-distance and long-value streaming guards. 76 tests cover detectors, vault, streaming (including a property-based chunk-partition round-trip), SSE, audit, and all five integrations.

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License

MIT (c) Godfrey Lebo / Raeven Company LTD

Reporting security issues

Email [e-mail]. Do not file public issues for security findings.