Signer private key usage

[o-tsaruk]

Hi! =)
May I know how exactly Alchemy uses private key when we sign and send transactions? Where is private key stored, and what we send to the (turnkey) server when execute transaction?
I know that the private key of the wallet is encrypted with a passkey, access to which is available only to the user on the device. But when logging in, is it sent to the client, or does the transaction take place outside the client?
Thanks!

[aashkrishnan]

Hey @o-tsaruk!

Yup, we’ve built our own signer powered by Turnkey. Turnkey does use secure enclaves that run in an AWS Nitro Enclave. Turnkey manages the keys but cannot access them. With Turnkey, keys are generated and used entirely inside a secure enclave (AWS Nitro Enclave), which is isolated from both the host machine and Turnkey itself. The private key never leaves the enclave, and Turnkey can’t access it. With its custom OS (QuorumOS), Turnkey ensures that only verified code runs in the enclave and no single engineer can reconstruct a secret or modify secure workloads.

When a transaction is initiated, what’s sent to Turnkey is only the transaction data that needs to be signed. This request is first sent to Alchemy, which adds its own signature (to satisfy the 2-of-2 multisig threshold), and forwards the request to Turnkey. Turnkey verifies both signatures (the user’s and Alchemy’s), signs the provided data using the private key inside the enclave, and returns only the resulting signature.

The private key remains securely inside the Nitro Enclave and is never exposed to Alchemy, the client, or even Turnkey outside the enclave.

When logging in, the private key is not sent to the client. Instead, the transaction signing happens outside the client, inside the enclave, which the client accesses through a secure session established in the browser (via an iframe). As part of the login flow (email OTP, social login), the user receives a credential bundle — an opaque blob that stays on the client and is used to establish and maintain this secure session.

Once the session is active, signing requests (like transactions or messages) are generated inside the Turnkey iframe, and the private key inside the enclave signs the data. The private key never leaves the enclave unless a user on the client chooses to export their keys.