Sensitive data scanning

A developer can paste a card number or a live API key into a prompt by mistake. Proxium is the last stop before the request goes to a vendor. So it is the last place where that value can still be stopped.

:::info State on proxium.tech Each project uses the default policy of the gateway until it sets its own classes. On proxium.tech the default is credit_card, card_security, iban, national_id and credential on redact, with an alert, and every other class off. You set each class on the Data protection screen. See Protect sensitive data. :::

What it finds

Class	Finds	Check against false matches
credit_card	Card numbers	The Luhn check digit
iban	Bank account numbers	The mod-97 check
email	Email addresses
phone	Phone numbers
credential	AWS, GitHub, Slack, Stripe, OpenAI, Anthropic, Google and GitLab keys, JWTs, private key blocks, passwords in URLs such as postgres://user:pass@host, Authorization: Bearer values, *_KEY=, *_SECRET= and *_TOKEN= assignments	The known format of each key, or a long random value after a secret word
card_security	An expiry date or a security code	Only near a card number
national_id	US SSN, UK National Insurance number, Romanian CNP, Spanish DNI and NIE, Italian codice fiscale	The check digit or check letter, or the strict structure of the number
ip_address	IPv4 and IPv6 addresses	Each part in range; no version numbers such as 1.2.3.4.5
custom	The words and phrases of your project's list	A whole word, in any case
prompt_injection	Known instruction-override shapes, also in base64

The scan reads the whole request body except the model field. Each matcher reads the text one time, from start to end, with no regular expressions. One automaton finds your terms in a single pass too. So a long or a hostile prompt cannot slow it down.

What it does with a match

Each class has one of four actions:

Action	The request	The match
off	Goes out unchanged	Not looked for
flag	Goes out unchanged	Logged, and an alert is sent
redact	Goes out with a placeholder in place of the value	Logged, and an alert if you turned it on
block	Is refused with 403 guardrail_blocked	Logged, and an alert if you turned it on

Use flag to watch real traffic before you choose redact or block.

Fig. 1 · what the scan does with a card number

Example: a request holds the text Refund card 4242 4242 4242 4242. Proxium scans it in one pass, before the response cache, the stored prompts, the memory and the vendor.

• credit_card on block: the call gets 403 guardrail_blocked. Nothing is sent or stored.
• credit_card on redact: the value becomes [REDACTED:credit_card:1]. Only the placeholder reaches the response cache, the stored prompts, the memory and the vendor.
• No match, or credit_card on flag: the request goes out unchanged. A flag logs the match and sends an alert.

A project on the default policy has credit_card, card_security, iban, national_id and credential on redact, with an alert.

Example. The prompt Refund card 4242 4242 4242 4242, please, with credit_card set to redact, goes to the vendor as Refund card [REDACTED:credit_card:1], please. The same value two times gets the same number, so the model can still tell that two mentions are one card.

With block, your app gets:

403 body

{
  "error": {
    "message": "blocked by egress guardrail: credit_card detected at /messages/0/content (the matched value is deliberately not echoed)",
    "type": "guardrail_blocked",
    "code": "guardrail_blocked"
  }
}

Where the value never goes

The scan runs first in a call, before the response cache, the stored prompts, the memory and the vendor. A redacted or blocked value is therefore never written anywhere.

Each match writes an audit record: the project, the app, the key prefix, the time, the class and the action. It also names the place in the request, such as /messages/0/content. The record never holds the matched value. The refusal message and the alert do not hold it either. A flag sends the value to the vendor unchanged, so it is in the stored prompts if your project keeps them.

Alerts

An alert goes to the channels of Settings › Spend alerts: Slack, Discord, Telegram or a webhook. Proxium sends at most one alert for each class and app in a short window. The alert says how many requests matched since the last alert of that class and app, and it never holds the value.

Related pages

• What Proxium does not do
• Data handling
• The request flow