burnedsecret — Official Python SDK for burnedsecret.com

When you put a secret into burnedsecret, your browser (or your client library) encrypts it on your own device before anything leaves you. The encryption key never goes to our server. We store an opaque blob of encrypted bytes; we cannot read it, and neither can anyone who breaches our database, subpoenas us, or gets a court order against us. We have nothing to hand over.

This package is the official Python client. All crypto runs in your process — the server only sees ciphertext, IVs, and (for the request flow) RSA-OAEP wrapped keys. The decryption material lives in your code (URL fragments, or PKCS8 bytes you stash in a KMS), never on our servers.

Installation

pip install burnedsecret

Python 3.10 or newer is required. The SDK pulls in cryptography>=42 and requests>=2.32 and nothing else.

Quick start

One-way secret (you share a password with someone)

from burnedsecret import BurnedSecret

bs = BurnedSecret(api_key="bs_...")

url, secret_id = bs.create_secret("hunter2", ttl=86400)
# url looks like: https://burnedsecret.com/s/<id>#k=<base64url AES key>
# the part after '#' never leaves the caller's process — browsers do not
# transmit URL fragments to servers, and this SDK only sends ciphertext + IV.

plaintext = bs.read_secret(url)   # burns the secret on read

Secret request (you ask someone to send you a password)

url, request_id, private_key = bs.create_request(
    prompt="Send me your AWS root key",
    webhook_url="https://acme.example/hooks/bs",
    ttl=86400,
)
# Persist `private_key` (PKCS8 DER bytes) — without it, the fulfillment is
# unrecoverable. Use bs.export_private_key(private_key) → str for KMS storage.

# Later, after the fulfiller has submitted their answer:
plaintext = bs.read_fulfillment(request_id, private_key)

When the request was created with custom fields, read_fulfillment returns a dict mapping field name → value instead of a string:

url, request_id, private_key = bs.create_request(
    prompt="Send me your AWS keypair",
    fields=[
        {"name": "access_key_id", "type": "text", "required": True},
        {"name": "secret_access_key", "type": "password", "required": True},
    ],
)
data = bs.read_fulfillment(request_id, private_key)
# data == {"access_key_id": "AKIA...", "secret_access_key": "wJal..."}

Storing private keys in your KMS

# At request-creation time:
url, request_id, priv = bs.create_request(prompt="...")
kms_blob = BurnedSecret.export_private_key(priv)   # str (base64url no-padding)
my_kms.put(f"bs/req/{request_id}", kms_blob)

# At fulfillment-retrieval time:
kms_blob = my_kms.get(f"bs/req/{request_id}")
priv = BurnedSecret.import_private_key(kms_blob)
plaintext = bs.read_fulfillment(request_id, priv)

Public-key handling

Your decryption material never goes to our servers. For requests, the SDK generates an RSA-4096 keypair locally and only sends the public key (SPKI DER, base64url). The private key is returned to you as PKCS8 DER bytes — persist it in your KMS or secret store. If you lose it, the fulfillment is unrecoverable. That's the whole point.

The SDK never derives or stores key material outside of the values you receive from create_secret (which returns the URL containing the key in its fragment) and create_request (which returns the private key bytes). Anything your process needs to keep, the SDK hands you and forgets.

Error handling

The SDK raises a small exception hierarchy:

BurnedSecretError
├── ApiError                  (HTTP-level failure; has .status_code, .code)
│   ├── NotFoundError         404 — secret/request not found
│   ├── BurnedError           410 — secret or fulfillment already consumed
│   ├── LegacyApiError        410 — pre-Phase-21 document, not API-accessible
│   └── RateLimitError        429 — has .retry_after_seconds
└── CryptoError               local AES/RSA failure (bad key, malformed data)

from burnedsecret import (
    BurnedSecret, BurnedError, NotFoundError, RateLimitError, CryptoError,
)

bs = BurnedSecret(api_key="bs_...")
try:
    plaintext = bs.read_secret(url)
except BurnedError:
    print("Secret has already been viewed and burned.")
except NotFoundError:
    print("Secret never existed or expired.")
except RateLimitError as e:
    print(f"Too many requests — retry after {e.retry_after_seconds}s")
except CryptoError:
    print("The URL fragment is wrong or the ciphertext is corrupted.")

BurnedSecret(api_key="...") itself raises ValueError when the API key is missing or does not start with bs_.

Test vectors and interop

The wire format — AES-256-GCM with a 12-byte IV and a 128-bit appended tag, RSA-OAEP-SHA256 over a 4096-bit modulus, SPKI/PKCS8 DER with base64url no padding — is pinned at https://burnedsecret.com/api/v1/test-vectors.json.

Any third-party Python implementation can prove conformance by round-tripping that file. The same file lives in this repo at web/api/v1/test-vectors.json and powers tests/test_interop.py, which asserts four invariants:

1. AES encrypt with secret.aes_key + iv + plaintext is byte-identical to secret.ciphertext.
2. AES decrypt of secret.ciphertext recovers secret.plaintext_utf8.
3. RSA-OAEP decrypt of request.wrapped_key with request.private_key_pkcs8 recovers request.content_aes_key.
4. AES encrypt with the unwrapped key reproduces request.ciphertext.

If your SDK round-trips all four, it is wire-compatible with this one and with the official JavaScript and Flutter clients.

Crypto specification

Full algorithm parameters, key formats, and design rationale: .planning/design/zero-knowledge-architecture.md in this repository.

Development

git clone https://github.com/JensrudJ/burnedsecret
cd burnedsecret/sdk-python
pip install -e ".[dev]"
pytest -v

The test suite has 18 cases: 4 interop conformance + 4 crypto round-trips + 6 client wire-contract + 4 error-mapping. The RSA-4096 keygen test is marked @pytest.mark.slow and runs in about three seconds; run pytest -v -m "not slow" to skip it during fast inner-loop iteration.

Releases

Releases are published from Codemagic on tags pushed to the burnedsecret repo:

• @burnedsecret/sdk (npm): tag matching sdk-js-vMAJOR.MINOR.PATCH
• burnedsecret (PyPI): tag matching sdk-py-vMAJOR.MINOR.PATCH

The version in the tag must match the version in package.json / pyproject.toml.

Every push to dev runs the test suite and the cross-SDK round-trip gate (D-15) but does NOT publish.

Each SDK release workflow also runs cross-SDK round trips at its own checkout before publishing. Built packages must pass clean consumer installation checks. A release tag must exactly match its package version; a tagged release fails if its publishing credential is missing. Builds and publication run in Codemagic.

License

MIT — see LICENSE in the repository root.

Authenticated envelope formats

File secrets now use BSF2, which authenticates the complete header and each chunk's position. Old BSF1 files are rejected; there is no legacy fallback. This is an intentional format break for previously disposable test data. Python 1.1.0, JavaScript 2.0.0 and the updated web file viewer use this format; JavaScript 1.2.0 does not support it.

Unprotected text remains raw UTF-8, including literal PP: strings. Protected SDK text uses a binary BSP2 marker that cannot collide with UTF-8 plaintext. Collect a passphrase before fetching a protected secret: a missing/wrong passphrase discovered after burn-on-read cannot be recovered by refetching. See the envelope specification for framing and interop vector version 3. Browser text protection is a separate flow; SDK passphrase-protected text still requires an SDK reader.