PXA3xx Boot ROM Reference Manual - Marvell

9 Trusted Boot OperationThe following sections provide information about trusted boot operations, including using a trustedimage module, trusted image module validation, flash support, image downloading, preprogrammedflash requirements, and JTAG reenablement.9.1 Trusted Boot Usage CasesThe trusted boot solution is based on the principle of the “chain of trust”, also referred to as layeredtrust (see Figure 8, “Trusted Boot Operation Using the Trusted Image Module). The Marvell ®Trusted Boot ROM is responsible only for securely transferring control to the next layer of software,which is the OEM boot module. The Boot ROM authenticates and checks the integrity of the imagewith the OEM’s platform public verification key. The OEM boot module establishes an OEM’sproprietary layered trust model to securely validate all of the OEM’s supplementary binaries (the OS,applications, data, and so on), as well as the mobile operator’s service provisioning and downloads.The layered solution is implemented using the trusted image module defined in Section 7 "TrustedImage Module" on page 71. The trusted image module holds the security information for some or allof the images loaded into the boot flash device. The trusted image module provides a flexiblemechanism for trusted boot operations using industry-standard RSA and SHA-1 operations.Each layer of software, starting with the Boot ROM, uses the information located in the trusted imagemodule to validate one or more images. The implementation defines the number of images toinclude in the trusted image module for validation, and which layer of software does the validation.Unauthorized modifications to the system software are identified and prevented from running on thesystem.The trusted image module is located in the flash memory, according to the usage models defined inthe following sections. All other image locations are defined in the trusted image module.12345678910111213141516171819202122232425262728293031323334353637383940414243444546474849505152535455565758Copyright © 2010 Marvell PUBLIC RELEASE Doc. No. MV-S301208-00 Rev. -Page 87