This application note explains the way to build the secure BL1(1st Bootloader) and BL2(2nd Bootloader) images in the booting environment of Exynos4212. iROM code(iROM Bootloader) of Exynos4212 confirms to download the BL1 image with checksum, verifies the integrity of the secure BL1 image, decrypts the secure BL1 image, and then iROM goes to BL1. In the BL1, the integrity of the secure BL2 is verified. If the secure BL2 image is verified successfully, BL1 will go to BL2. In order to verify the integrity of the secure image on each stage, iROM code provides the secure library functions to reuse in BL1 and BL2.