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Apple System Restore (also known as ASR) is an application found on the Ramdisks of an IPSW firmware file. It works by writing the rootfs image to the actual system drive (ASR RESTORE), then checksums it. (ASR VERIFY)

ASR Verify Disassembly

__text:00014204 loc_14204                               ; CODE XREF: sub_13AB4+61E�j
__text:00014204                                         ; sub_13AB4+73E�j
__text:00014204                 LDR     R3, =(off_235E8 - 0x1420A)
__text:00014206                 ADD     R3, PC
__text:00014208                 LDR     R3, [R3]
__text:0001420A                 LDR     R3, [R3]
__text:0001420C                 CMP     R3, #0
__text:0001420E                 BEQ     loc_1427A
__text:00014210                 LDR     R0, =(aImagePassedSig - 0x14216)
__text:00014212                 ADD     R0, PC          ; "Image passed signature verification"
__text:00014214                 BLX     _warnx
__text:00014218                 B       loc_1427A
__text:0001421A ; ---------------------------------------------------------------------------
__text:0001421A loc_1421A                               ; CODE XREF: sub_13AB4+622�j
__text:0001421A                                         ; sub_13AB4+628�j ...
__text:0001421A                 LDR.W   R0, =(aImageFailedSig - 0x14222)
__text:0001421E                 ADD     R0, PC          ; "Image failed signature verification"
__text:00014220                 BLX     _warnx
__text:00014224                 MOVS    R2, #0x50
__text:00014226                 B       loc_1426E
__text:00014228 ; ---------------------------------------------------------------------------

See Also

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