Pre-boot authentication or power-on authentication serves as an extension of the BIOS, UEFI or boot firmware and guarantees a secure, tamper-proof environment external to the operating system as a trusted authentication layer. The PBA prevents anything being read from the hard disk such as the operating system until the user has confirmed they have the correct password or other credentials including multi-factor authentication.
A PBA environment serves as an extension of the BIOS, UEFI or boot firmware and guarantees a secure, tamper-proof environment external to the operating system as a trusted authentication layer. The PBA prevents Windows or any other operating system from loading until the user has confirmed he/she has the correct password to unlock the computer. That trusted layer eliminates the possibility that one of the millions of lines of OS code can compromise the privacy of personal or company data.
Pre-boot authentication can by performed by an add-on of the operating system like Linux Initial ramdisk or Microsoft's boot software of the system partition or by a variety of full disk encryption vendors that can be installed separately to the operating system. Legacy FDE systems tended to rely upon PBA as their primary control. These systems have been replaced by systems using hardware-based dual-factor systems like TPM chips or other proven cryptographic approaches. However, without any form of authentication, encryption provides little protection from advanced attackers as this authentication-less encryption fully rely on the post-boot authentication comes from Active Directory authentication at the GINA step of Windows.
Security concerns
Microsoft released BitLocker Countermeasures defining protection schemes for Windows. For mobile devices that can be stolen and attackers gain permanent physical access Microsoft advise the use of pre-boot authentication and to disable standby power management. Pre-boot authentication can be performed with TPM with PIN protector or any 3rd party FDA vendor. Best security is offered by offloading the cryptographic encryption keys from the protected client and supplying key material externally within the user authentication process. This method eliminates attacks on any build-in authentication method that are weaker than a brute-force attack to the symmetric AES keys used for full disk encryption. Without cryptographic protection of a hardware supported secure boot environment, PBA is easily defeated with Evil Maid style of attacks. However, with modern hardware most FDE solutions are able to ensure that removal of hardware for brute-force attacks is no longer possible.
Authentication methods
The standard complement of authentication methods exist for pre-boot authentication including:
