Pre-boot authentication (PBA) or power-on authentication (POA)
serves as an extension of the
BIOS
In computing, BIOS (, ; Basic Input/Output System, also known as the System BIOS, ROM BIOS, BIOS ROM or PC BIOS) is firmware used to provide runtime services for operating systems and programs and to perform hardware initialization during the ...
,
UEFI
UEFI (Unified Extensible Firmware Interface) is a set of specifications written by the UEFI Forum. They define the architecture of the platform firmware used for booting and its interface for interaction with the operating system. Examples ...
or boot firmware and guarantees a secure, tamper-proof environment external to the
operating system
An operating system (OS) is system software that manages computer hardware, software resources, and provides common daemon (computing), services for computer programs.
Time-sharing operating systems scheduler (computing), schedule tasks for ef ...
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
Multi-factor authentication (MFA; encompassing two-factor authentication, or 2FA, along with similar terms) is an electronic authentication method in which a user is granted access to a website or application only after successfully presenting ...
.
Uses of pre-boot authentication
*
Full disk encryption outside of the operating system level
*
Encryption
In cryptography, encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can dec ...
of temporary files
*
Data at rest protection
*
Encryption
In cryptography, encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can dec ...
of cloud servers or instances
Pre-boot authentication process
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 any 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.
Generic boot sequence
in BIOS mode:
#
Basic Input/Output System (BIOS)
#
Master boot record
A master boot record (MBR) is a special type of boot sector at the very beginning of partitioned computer mass storage devices like fixed disks or removable drives intended for use with IBM PC-compatible systems and beyond. The concept of MB ...
(MBR) partition table
# Pre-boot authentication (PBA)
#
Operating system
An operating system (OS) is system software that manages computer hardware, software resources, and provides common daemon (computing), services for computer programs.
Time-sharing operating systems scheduler (computing), schedule tasks for ef ...
(OS) boots
in UEFI mode:
#UEFI (
Unified Extensible Firmware Interface
UEFI (Unified Extensible Firmware Interface) is a set of specifications written by the UEFI Forum. They define the architecture of the platform firmware used for booting and its interface for interaction with the operating system. Examples ...
)
#
GUID Partition Table
The GUID Partition Table (GPT) is a standard for the layout of partition tables of a physical computer storage device, such as a hard disk drive or solid-state drive, using universally unique identifiers, which are also known as globally unique ...
(GPT)
# Pre-boot authentication (PBA)
#
Operating system
An operating system (OS) is system software that manages computer hardware, software resources, and provides common daemon (computing), services for computer programs.
Time-sharing operating systems scheduler (computing), schedule tasks for ef ...
(OS) boots
Pre-boot authentication technologies
Combinations with full disk encryption
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 boot partition) or by a variety of
full disk encryption (FDE) 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 (e.g. a fully transparent authentication loading hidden keys), encryption provides little protection from advanced attackers as this authentication-less encryption fully rely on the post-boot authentication comes from
Active Directory
Active Directory (AD) is a directory service developed by Microsoft for Windows domain networks. It is included in most Windows Server operating systems as a set of processes and services. Initially, Active Directory was used only for centr ...
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 (paragraph Attacker with skill and lengthy 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 built-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 (TPM) supported secure boot environment, PBA is easily defeated with
Evil Maid style of attacks. However, with modern hardware (including
TPM or cryptographic multi-factor authentication) 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:
# Something you know (e.g. username/password like Active Directory credentials or TPM pin)
# Something you have (e.g.
smart card
A smart card, chip card, or integrated circuit card (ICC or IC card) is a physical electronic authentication device, used to control access to a resource. It is typically a plastic credit card-sized card with an embedded integrated circuit (IC) c ...
or other token)
#Something you are (e.g. biometric attributes like fingerprint, face recognition, iris scan)
#Automatic authentication in trusted zones (e.g. boot key provided to company devices by the enterprise network)
References
{{DEFAULTSORT:Pre-Boot Authentication
Computer access control