Secure handling of customer-supplied encryption secrets

An application server sends a public key from an asynchronous key-pair to a user system to encrypt a user encryption secret that forms part of a first encryption key. The application server uses a second encryption key provided by a key derivation server to encrypt a private key from the asynchronous key-pair. The application server then deletes the second encryption key to prevent decryption of the user encryption secret received from the user system. The application server receives the encrypted user encryption secret from the user system and sends a request to the key derivation server to re-encrypt the user encryption secret. The key derivation server uses a key encryption secret to generate the second encryption key and decrypt the private key. The key derivation server uses the decrypted private key to decrypt the user encryption secret and then re-encrypts the first encryption secret to prevent decryption by the application server.