CubeSigner is what staking operators and bridges use when they need arbitrary policy code to run next to the key: HSM-sealed keys, Nitro Enclaves, and a programmable policy engine that executes your Rust or Wasm inside the TEE. Coldstar is a smaller idea, aimed at agents and treasuries rather than validators.
CubeSigner for validator and protocol infrastructure; Coldstar for the operator treasury and agents that spend from it.
| Coldstar | Cubist CubeSigner | |
|---|---|---|
| Who holds the root key | You. The cold root lives encrypted on your own USB drive. No vendor holds a key, a share, or an account. | Cubist's enclaves. Only the enclave can access keys in the HSM; Cubist says not even its administrators can see keys. Imported keys encrypt directly to the enclave; cold-storage backup ciphertexts decrypt only for the owner. |
| Where the key lives | On your machine. The air-gapped root signs a bounded policy envelope; a disposable session key signs routine transactions inside it. | AWS Nitro Enclaves plus KMS and FIPS 140 HSMs, TPM 2.0 attestation; explicitly not Intel SGX. |
| Policy engine | Per-transaction limit, daily cap, program allowlist, recipient allowlist and blocklist, escalate-above threshold. Evaluated locally, first match wins, before any signature exists. | Built-ins: receiver allowlist, RequireMfa with approver count and MFA types. Programmable Policy Engine runs custom Rust/Wasm in the TEE. Signature issued only if all checks pass. Solana instruction-level built-ins not confirmed. |
| Out-of-policy transactions | ESCALATE to a human over air-gapped QR, or REJECT. No signature is produced for a rejected transaction. | Denied, or held for MFA by N approvers. |
| Cold / offline root | Yes — the root key never touches a networked machine. | No offline signing root. Owner-decryptable cold backup ciphertexts exist. |
| Agent integration | Framework-agnostic: the agent proposes an unsigned transaction, the signer decides. CLI signer today; MCP server in progress. | No dedicated AI-agent product or docs found. |
| Solana support | Solana mainnet. Core is chain-agnostic; EVM signing exists. | Yes: SDK supports Bitcoin and Solana alongside EVM. |
| Source & self-hosting | Open source (MIT), self-hosted. No API key, no SaaS dependency, nothing to go down. | SDKs public; enclave and policy runtime closed. Hosted. |
| Pricing | Free software plus a ~$10 drive. | Not public; contact sales. |
| Maturity | Beta — the signing core and policy engine are in scope for the planned independent audit. | Production; audited by Veridise (ongoing); SOC 2 referenced. |
CubeSigner's programmable policies are the most powerful in this set. They are also code you write and maintain inside someone else's runtime. Coldstar trades that power for a rule list you can read in a minute and a root that is never online.
CubeSigner's promise is complete mediation: every signature passes through policy code executing inside an attested enclave, with the key sealed in an HSM. That is a strong model for infrastructure that must sign constantly and cannot have a human in the loop. You trust Cubist's enclave operation and your own policy code.
Coldstar's promise is that the root is never reachable: it lives encrypted on a drive, signs a policy envelope offline, and the agent works from a disposable session key under a short, fixed rule list evaluated locally. Less power, less to get wrong, nothing to attest.
CubeSigner is production and audited. Coldstar is beta, pre-audit.
For most agents, yes; it is built for validators, bridges, and exchanges. Its programmable policies would work for agents, but Cubist publishes no agent documentation or pricing.
No. Coldstar's policy is a fixed, ordered rule list: blocklist, program allowlist, escalate threshold, per-transaction limit, recipient allowlist, daily cap. That is deliberate; a rule list is easier to audit than a runtime.
Different jobs. CubeSigner defends an always-online key with hardware and attestation. Coldstar keeps the root offline and limits what the online part can do.
Open source, MIT. macOS, Linux, Windows — and on the Solana Seeker dApp Store.
pip install coldstar
Third-party facts were checked against the vendor's own pages on the date above. Pricing and feature sets change; if something here is out of date, tell us and we will fix it.