Crypto Keys overview

KnoxCall’s Crypto Keys feature is encryption-as-a-service. You create a named key, then encrypt and decrypt data through KnoxCall’s API. Your applications never see the key material — they call /encrypt and /decrypt and get back ciphertext / plaintext. The Vault parallel: this is KnoxCall’s transit engine. Use it for:

Encrypting customer-record fields at the application layer (PII, PHI, PCI).
Decoupling apps from key storage — change the key, rotate it, destroy it without touching application code.
Cryptographic erasure — destroy a key version and every piece of ciphertext under it becomes permanently unreadable. Powerful right-to-be-forgotten primitive.
Centralised audit — every encrypt / decrypt call lands in the audit log.

Quick example

# Create a named key
curl -X POST https://api.knoxcall.com/v1/crypto/keys \
  -H "Authorization: Bearer $KC_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{ "name": "customer-pii", "mode": "cloud-only" }'

# Encrypt some plaintext
curl -X POST https://api.knoxcall.com/v1/crypto/keys/customer-pii/encrypt \
  -H "Authorization: Bearer $KC_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{ "plaintext": "Jane Doe, 415-555-9311" }'
# → { "ciphertext": "knoxcall:v1:G2x...", "key_version": 1 }

# Decrypt it (any version that hasn't been destroyed)
curl -X POST https://api.knoxcall.com/v1/crypto/keys/customer-pii/decrypt \
  -H "Authorization: Bearer $KC_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{ "ciphertext": "knoxcall:v1:G2x..." }'
# → { "plaintext": "Jane Doe, 415-555-9311", "plaintext_b64": "SmFuZSBEb2UsIDQxNS01NTUtOTMxMQ==", "key_version": 1 }

The ciphertext format is knoxcall:v<N>:<base64-payload> where N is the key version that produced it. Vault’s vault:v<N>:... prefix is also accepted on input — you can migrate ciphertext stored under Vault’s transit engine without re-encrypting.

Algorithms

Pick a key_type when you create a key. The right choice depends on what you’ll use it for:

`key_type`	Use case	Operations
`aes256-gcm`	Encrypt/decrypt application data	`encrypt`, `decrypt`, `rewrap`
`hmac-sha256`, `hmac-sha512`	HMAC over a payload (request signing, webhook auth)	`hmacSign`, `hmacVerify`, `signJwt`, `verifyJwt`
`rsa-2048`, `rsa-3072`, `rsa-4096`	Asymmetric signing — JWTs (RS256/PS256), document signing	`sign`, `verify`, `signJwt`, `verifyJwt`, `getPublicKey`
`ecdsa-p256`, `ecdsa-p384`	Asymmetric signing — JWTs (ES256/ES384), faster than RSA	`sign`, `verify`, `signJwt`, `verifyJwt`, `getPublicKey`
`ed25519`	Modern asymmetric signing — JWTs (EdDSA), constant-time	`sign`, `verify`, `signJwt`, `verifyJwt`, `getPublicKey`

Cryptographic primitives:

AES-256-GCM. Ciphertext payload iv[12] || authTag[16] || ciphertext[n]. Format-prefix knoxcall:v<N>:<base64>.
HMAC: SHA-256 (32-byte tag) or SHA-512 (64-byte tag).
RSA: PKCS#1 v1.5 padding by default for JWT compatibility (RS256). PSS available via rsa_padding: 'pss' for raw signing, or header_overrides: { alg: 'PS256' } (/ PS384, PS512) for JWT signing.
ECDSA: deterministic per RFC 6979.
Ed25519: standard EdDSA.

Public key export: asymmetric keys expose GET /v1/crypto/keys/{name}/public-key returning both PEM (SPKI) and JWK. External services verify your signatures using the public key without ever needing the private side.

JWT signing and verification

Use a key directly to sign / verify JWTs:

# Sign
curl -X POST https://api.knoxcall.com/v1/crypto/keys/jwt-signer/jwt \
  -H "Authorization: Bearer $KC_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{ "claims": { "sub": "user-123", "exp": 9999999999 } }'
# → { "data": { "token": "eyJ...", "key_version": 1, "alg": "RS256" }, "meta": { "request_id": "..." } }

# Verify
curl -X POST https://api.knoxcall.com/v1/crypto/keys/jwt-signer/jwt/verify \
  -H "Authorization: Bearer $KC_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{ "token": "eyJ..." }'
# → { "data": { "valid": true, "claims": { ... }, "key_version": 1, "alg": "RS256" }, "meta": { "request_id": "..." } }

The alg is derived from the key (hmac-sha256 → HS256, rsa-2048 → RS256, ecdsa-p256 → ES256, ed25519 → EdDSA). The verifier:

rejects alg: 'none' unconditionally,
rejects algorithm confusion — an HS256 token won’t verify against an RSA key,
binds kid so the version that issued the token is the one used to verify,
validates standard claims when you pass expected (issuer, audience, subject, expiry, clock skew).

External verify (the killer test): export the public key, hand it to jsonwebtoken in Node or pyjwt in Python, and verify a token KnoxCall signed. If those libraries accept it, the implementation is end-to-end correct.

Webhook signing helper

For Stripe-format webhook signatures (v1 supports the Stripe t=<unix>,v1=<hex> format; additional formats are planned), use the helper:

curl -X POST https://api.knoxcall.com/v1/crypto/keys/stripe-webhook-secret/webhook-sign \
  -H "Authorization: Bearer $KC_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{ "payload": "{\"event\":\"order.completed\"}" }'
# → { "data": { "signature_header": "t=1735000000,v1=<hex>", "timestamp_seconds": 1735000000, "key_version": 1, "format": "stripe" }, "meta": { "request_id": "..." } }

This is the same signing logic Webhook Signing uses for outbound subscriptions, exposed as a primitive so you can sign payloads with full control over headers and timing.

Modes

When you create a key, pick a mode:

`cloud-only` (recommended)

Key material stays on KnoxCall’s control plane. Every encrypt / decrypt is a network call.

✅ Strongest blast-radius story — a self-hosted agent or local app process can never leak the key.
⚠️ Higher latency — every operation is a round-trip to KnoxCall.
👍 Use for: high-value secrets (PCI cardholder data, PHI), audit-driven encryption (every call is logged), keys you might ever want to revoke.

`bundled`

Key material is shipped to self-hosted agents in their session bundle (encrypted with the session key) so the agent can do encrypt / decrypt locally, without the call leaving the customer’s network.

✅ Low-latency local encrypt / decrypt.
✅ Same trust model as KnoxCall’s secret-injection feature today — in-memory, hour-bounded.
⚠️ A compromised agent process can read the in-memory key for the duration of its session.
👍 Use for: hot-path encryption inside a trusted self-hosted environment where round-trips would be too slow.

The mode is a one-shot decision per key — to switch, create a new key in the other mode and rewrap ciphertext to it.

Operations

Op	What it does	When to use
`encrypt`	Plaintext → ciphertext, tagged with current version	Every encryption op
`decrypt`	Ciphertext → plaintext, using whatever version the prefix names	Every decryption op
`rotate`	Mints a new active version, retires the previous	Periodic key hygiene; after a suspected compromise
`rewrap`	Decrypts with old version + re-encrypts with active. Plaintext never crosses the wire.	Migrating old ciphertext to a fresh version after a rotate
`destroyVersion`	Cryptographic erasure of a specific version	Right-to-be-forgotten; after rewrap migration is done
`hmacSign` / `hmacVerify`	Keyed HMAC over a payload	API request signing, message authentication
`sign` / `verify`	Asymmetric sign / verify (RSA, ECDSA, Ed25519)	Document signing, custom-format signing
`signJwt` / `verifyJwt`	Issue or validate a JWT	Service-to-service auth, customer-facing tokens
`webhookSign`	Stripe-format `t=...,v1=...` header	Outbound webhook signing primitive
`getPublicKey`	Export the public side of an asymmetric key (PEM + JWK)	Hand to external verifiers

Versioning at a glance

customer-pii (current_version = 3)
  v3  active     ← encrypt uses this
  v2  retired    ← can still decrypt v2 ciphertext
  v1  destroyed  ← v1 ciphertext is permanently unreadable

Encrypt always uses the active version.
Decrypt uses the version named in the ciphertext prefix.
Retired versions stay around so legacy ciphertext keeps working.
Destroyed versions are cryptographic erasure — that ciphertext is permanently unreadable. (You can’t destroy the active version; rotate first.)

deletion_allowed is a per-key safety latch. Set it false on production keys to require explicitly flipping the latch before any version can be destroyed. See Rotation & versioning for the full lifecycle.

How the keys themselves are protected

Each version is stored wrapped with your tenant master key (KCT1 envelope format). When KnoxCall needs to use a version, it unwraps it on the fly into an in-memory cache (5-minute TTL). If you cryptographically erase your tenant master key, every transit key under it becomes permanently unreadable — by construction. There’s no separate “delete all keys” step; the wrapping chain does it.

Audit trail

Every encrypt / decrypt / rotate / destroy lands in the audit log under resource_type='transit' with the key name, version, and caller. You can answer “who decrypted PII record 12345 last Tuesday?” in two log queries.

Plays well with…

Routes — store an encrypted secret in a route header by encrypting it with a transit key and decrypting on egress.
Databases — encrypt PII in your own DB schema; decrypt only on read.
Vaults — every vault gets its own AES-256-GCM Crypto Key. Rotate the vault → rotates the underlying transit key.
Webhook Signing (outbound) — sign payloads with hmacSign (HMAC formats) or sign (RSA/ECDSA/Ed25519). webhookSign returns a Stripe-shaped header in one call.
Inbound Webhooks — point a subscription at an HMAC key here instead of pre-sharing a secret; rotation flows through the Crypto Keys lifecycle.
Ephemeral Proxy — {{ encrypted | json: ... }} template references encrypt small JSON blobs with a Crypto Key.

​Crypto Keys overview

​Quick example

​Algorithms

​JWT signing and verification

​Webhook signing helper

​Modes

​cloud-only (recommended)

​bundled

​Operations

​Versioning at a glance

​How the keys themselves are protected

​Audit trail

​Plays well with…

​Next steps