Access Code
Here's the program cartridge for the satellite terminal's login system. We need the access code to start exploring the system.
AccessCode.peg
Disassemble the code using the debugger:
@puts:
0300.0000: MOV A3, 0x7F
0304.0000: LDB A1, [A0]
0306.0000: INC A0, 1
0308.0000: AND A2, A1, A3
030B.0000: WRB (0), A2
030D.0000: CMP A1, A2
030F.0000: BRR.NE @puts+0x4 //0304.0000
0312.0000: RET
@print_hex_byte:
0314.0000: ADD A5, PC, 0x3A
0319.0000: SRU A3, A0, 0x4
031D.0000: LDB A4, [A5 + A3]
0320.0000: WRB (0), A4
0322.0000: AND A0, 0xF
0326.0000: LDB A4, [A5 + A0]
0329.0000: WRB (0), A4
032B.0000: RET
@print_hex:
032D.0000: MOV A1, A1
032F.0000: RET.EQ
0331.0000: ADD A5, PC, 0x1D
0336.0000: LDB A2, [A0]
0338.0000: SRU A3, A2, 0x4
033C.0000: LDB A4, [A5 + A3]
033F.0000: WRB (0), A4
0341.0000: AND A2, 0xF
0345.0000: LDB A4, [A5 + A2]
0348.0000: WRB (0), A4
034A.0000: INC A0, 1
034C.0000: INC A1, -1
034E.0000: BRR.NE @print_hex+0x9 //0336.0000
0351.0000: RET
0353.0000: LDW.NE A2, [A0]
0355.0000: LDB.NE A2, [A2]
0357.0000: BRA.NE A2, A4
0359.0000: FCA.NE A2, S0
035B.0000: RDB.NE A2, (9)
035D.0000: SUB.LE A5, A1
035F.0000: MLS.LE A5, A3
0361.0000: DVS.LE A5, A5
@gimli_dump_state:
0363.0000: PSH {S0-S1, FP, RA-RD}
0366.0000: INC FP, SP, 4
0369.0000: MOV S0, A0
036B.0000: WRB (0), 0x20
036E.0000: WRB (0), 0x20
0371.0000: MOV S1, ZERO
0373.0000: MOV S1, S1
0375.0000: BRR.EQ @gimli_dump_state+0x31 //0394.0000
0378.0000: AND ZERO, S1, 0xF
037D.0000: BRR.NE @gimli_dump_state+0x29 //038C.0000
0380.0000: WRB (0), 0xA
0383.0000: WRB (0), 0x20
0386.0000: WRB (0), 0x20
0389.0000: BRR @gimli_dump_state+0x31 //0394.0000
038C.0000: AND ZERO, S1, 0x3
0391.0000: WRB.EQ (0), 0x20
0394.0000: LDB A0, [S0 + S1]
0397.0000: FCR @print_hex_byte
039A.0000: INC S1, 1
039C.0000: CMP S1, 0x30
03A0.0000: BRR.LT @gimli_dump_state+0x10 //0373.0000
03A3.0000: WRB (0), 0xA
03A6.0000: INC SP, FP, -4
03A9.0000: POP {S0-S1, FP, PC-DPC}
03AC.0000: SUB.GE FP, A0
03AE.0000: SUB.GE FP, A0
03B0.0000: SUB.GE RA, S0
03B2.0000: SHL PC, RD
03B4.0000: MOV PC, S2
03B6.0000: SUB.GE FP, A0
03B8.0000: SUB.GE FP, A0
03BA.0000: SUB.GE ZERO, FP
@gimli:
03BC.0000: PSH {S0-FP, RA-RD}
03BF.0000: MOV A1, 0x18
03C3.0000: PSH {A1}
03C6.0000: MOV A2, ZERO
03C8.0000: POP A0, {A3-A4}
03CC.0000: SHL RA, A3, 0x8
03D0.0000: SHL RD, A4, 0x8
03D4.0000: SRU A3, 0x8
03D7.0000: ORR A3, RD
03D9.0000: SRU A4, 0x8
03DC.0000: ORR A4, RA
03DE.0000: ADD A0, 0xC
03E2.0000: POP A0, {A5-S0}
03E6.0000: SRU RA, A5, 0x7
03EA.0000: SRU RD, S0, 0x7
03EE.0000: SHL A5, 0x9
03F1.0000: ORR A5, RD
03F3.0000: SHL S0, 0x9
03F6.0000: ORR S0, RA
03F8.0000: ADD A0, 0xC
03FC.0000: POP A0, {S1-S2}
0400.0000: AND RA, A5, S1
0403.0000: AND RD, S0, S2
0406.0000: SRU A1, RA, 0xE
040A.0000: SHL RA, 0x2
040D.0000: SHL RD, 0x2
0410.0000: ORR RD, A1
0412.0000: SHL FP, S2, 0x1
0416.0000: SHL A1, S1, 0x1
041A.0000: ORR.GE FP, 0x1
041E.0000: XOR RA, A1
0420.0000: XOR RD, FP
0422.0000: XOR RA, A3
0424.0000: XOR RD, A4
0426.0000: PSH A0, {RA-RD}
042A.0000: ORR RA, A3, S1
042D.0000: ORR RD, A4, S2
0430.0000: SHL RD, 0x1
0433.0000: SHL RA, 0x1
0436.0000: ORR.GE RD, 0x1
043A.0000: XOR RA, A3
043C.0000: XOR RD, A4
043E.0000: XOR RA, A5
0440.0000: XOR RD, S0
0442.0000: SUB A0, 0xC
0446.0000: PSH A0, {RA-RD}
044A.0000: AND RA, A3, A5
044D.0000: AND RD, A4, S0
0450.0000: SRU A1, RA, 0xD
0454.0000: SHL RA, 0x3
0457.0000: SHL RD, 0x3
045A.0000: ORR RD, A1
045C.0000: XOR RA, A5
045E.0000: XOR RD, S0
0460.0000: XOR RA, S1
0462.0000: XOR RD, S2
0464.0000: SUB A0, 0xC
0468.0000: PSH A0, {RA-RD}
046C.0000: INC A0, 4
046E.0000: INC A2, 1
0470.0000: CMP A2, 0x4
0474.0000: BRR.LT @gimli+0xc //03C8.0000
0477.0000: SUB A0, 0x10
047B.0000: POP {A1}
047E.0000: SRU A2, A1, 0x1
0482.0000: BRR.GE @gimli+0x125 //04E1.0000
0485.0000: SRU A2, 0x1
0488.0000: BRR.GE @gimli+0xf9 //04B5.0000
048B.0000: POP A0, {A3-S0}
048F.0000: PSH A0, {A3-A4}
0493.0000: XOR S0, 0x9E37
0497.0000: ORR A3, A1, 0x7900
049C.0000: XOR A5, A3
049E.0000: PSH A0, {A5-S0}
04A2.0000: INC A0, 8
04A4.0000: POP A0, {A3-S0}
04A8.0000: PSH A0, {A3-A4}
04AC.0000: PSH A0, {A5-S0}
04B0.0000: INC A0, -8
04B2.0000: BRR @gimli+0x125 //04E1.0000
04B5.0000: POP A0, {A3-A4}
04B9.0000: INC A0, 4
04BB.0000: POP A0, {A5-S0}
04BF.0000: PSH A0, {A3-A4}
04C3.0000: INC A0, -4
04C5.0000: PSH A0, {A5-S0}
04C9.0000: INC A0, 4
04CB.0000: POP A0, {A3-A4}
04CF.0000: INC A0, 4
04D1.0000: POP A0, {A5-S0}
04D5.0000: PSH A0, {A3-A4}
04D9.0000: INC A0, -4
04DB.0000: PSH A0, {A5-S0}
04DF.0000: INC A0, -4
04E1.0000: INC A1, -1
04E3.0000: BRR.NE @gimli+0x7 //03C3.0000
04E6.0000: POP {S0-FP, PC-DPC}
@gimli_absorb_byte:
04E9.0000: LDW A2, [A0 + 0x30]
04EE.0000: ADD A2, A0
04F0.0000: LDB A3, [A2]
04F2.0000: XOR A3, A1
04F4.0000: STB [A2],A3
04F6.0000: RET
@gimli_squeeze_byte:
04F8.0000: LDW A1, [A0 + 0x30]
04FD.0000: ADD A0, A1
04FF.0000: LDB A0, [A0]
0501.0000: RET
@gimli_advance:
0503.0000: ADD A1, A0, 0x30
0508.0000: LDW A2, [A1]
050A.0000: INC A2, 1
050C.0000: STW [A1],A2
050E.0000: CMP A2, 0x10
0512.0000: RET.NE
0514.0000: PSH {A1, RA-RD}
0517.0000: FCR @gimli
051A.0000: POP {A1}
051D.0000: STW [A1],ZERO
051F.0000: POP {PC-DPC}
@gimli_absorb:
0522.0000: MOV A2, A2
0524.0000: RET.EQ
0526.0000: PSH {S0-FP, RA-RD}
0529.0000: INC FP, SP, 6
052C.0000: MOV S0, A0
052E.0000: MOV S1, A1
0530.0000: MOV S2, A2
0532.0000: LDB A1, [S1]
0534.0000: INC S1, 1
0536.0000: MOV A0, S0
0538.0000: FCR @gimli_absorb_byte
053B.0000: MOV A0, S0
053D.0000: FCR @gimli_advance
0540.0000: INC S2, -1
0542.0000: BRR.NE @gimli_hash_update+0x10 //0532.0000
0545.0000: INC SP, FP, -6
0548.0000: POP {S0-FP, PC-DPC}
@gimli_squeeze:
054B.0000: MOV A2, A2
054D.0000: RET.EQ
054F.0000: PSH {S0-FP, RA-RD}
0552.0000: INC FP, SP, 6
0555.0000: MOV S0, A0
0557.0000: MOV S1, A1
0559.0000: MOV S2, A2
055B.0000: ADD A0, 0x30
055F.0000: MOV A1, 0xF
0563.0000: STW [A0],A1
0565.0000: MOV A0, S0
0567.0000: FCR @gimli_advance
056A.0000: MOV A0, S0
056C.0000: FCR @gimli_squeeze_byte
056F.0000: STB [S1],A0
0571.0000: INC S1, 1
0573.0000: INC S2, -1
0575.0000: BRR.NE @gimli_squeeze+0x1a //0565.0000
0578.0000: INC SP, FP, -6
057B.0000: POP {S0-FP, PC-DPC}
@gimli_pad:
057E.0000: PSH {A0, FP, RA-RD}
0581.0000: INC FP, SP, 2
0584.0000: MOV A1, 0x1
0588.0000: FCR @gimli_absorb_byte
058B.0000: POP {A0}
058E.0000: ADD A0, 0x2F
0592.0000: LDB A1, [A0]
0594.0000: XOR A1, 0x1
0598.0000: STB [A0],A1
059A.0000: MOV SP, FP
059C.0000: POP {FP, PC-DPC}
@gimli_hash_init:
059F.0000: MOV A1, ZERO
05A1.0000: MOV A2, ZERO
05A3.0000: MOV A3, ZERO
05A5.0000: ADD A0, 0x30
05A9.0000: STW [A0],ZERO
05AB.0000: PSH A0, {ZERO, A1-A3}
05AF.0000: PSH A0, {ZERO, A1-A3}
05B3.0000: PSH A0, {ZERO, A1-A3}
05B7.0000: PSH A0, {ZERO, A1-A3}
05BB.0000: PSH A0, {ZERO, A1-A3}
05BF.0000: PSH A0, {ZERO, A1-A3}
05C3.0000: RET
@gimli_hash_final:
05C5.0000: PSH {A0-A2, FP, RA-RD}
05C8.0000: INC FP, SP, 6
05CB.0000: FCR @gimli_pad
05CE.0000: POP {A0-A2}
05D1.0000: FCR @gimli_squeeze
05D4.0000: POP {FP, PC-DPC}
@gimli_hash:
05D7.0000: PSH {A0-A3, FP, RA-RD}
05DA.0000: INC FP, SP, 8
05DD.0000: SUB SP, 0x32
05E1.0000: MOV A0, SP
05E3.0000: FCR @gimli_hash_init
05E6.0000: ADD A5, SP, 0x36
05EB.0000: POP A5, {A1-A2}
05EF.0000: MOV A0, SP
05F1.0000: FCR @gimli_absorb
05F4.0000: ADD A5, SP, 0x32
05F9.0000: POP A5, {A1-A2}
05FD.0000: MOV A0, SP
05FF.0000: FCR @gimli_hash_final
0602.0000: MOV SP, FP
0604.0000: POP {FP, PC-DPC}
@memcmp8:
0607.0000: MOV A3, A0
0609.0000: LDB A4, [A3]
060B.0000: LDB A5, [A1]
060D.0000: SUB A0, A4, A5
0610.0000: RET.NE
0612.0000: INC A3, 1
0614.0000: INC A1, 1
0616.0000: INC A2, -1
0618.0000: BRR.NE @memcmp8+0x2 //0609.0000
061B.0000: RET
@memcmp16:
061D.0000: MOV A3, A0
061F.0000: LDW A4, [A3]
0621.0000: LDW A5, [A1]
0623.0000: SUB A0, A4, A5
0626.0000: RET.NE
0628.0000: INC A3, 2
062A.0000: INC A1, 2
062C.0000: INC A2, -2
062E.0000: BRR.NE @memcmp16+0x2 //061F.0000
0631.0000: RET
@memcmp:
0633.0000: MOV A2, A2
0635.0000: MOV.EQ A0, ZERO
0637.0000: RET.EQ
0639.0000: MOV A3, A0
063B.0000: AND A4, A3, 0x1
0640.0000: AND A5, A1, 0x1
0645.0000: XOR A4, A5
0647.0000: BRR.NE @memcmp8+0x2 //0609.0000
064A.0000: MOV A4, A4
064C.0000: BRR.EQ @memcmp+0x2d //0660.0000
064F.0000: LDB A4, [A3]
0651.0000: LDB A5, [A1]
0653.0000: SUB A0, A4, A5
0656.0000: RET.NE
0658.0000: INC A3, 1
065A.0000: INC A1, 1
065C.0000: INC A2, -1
065E.0000: RET.EQ
0660.0000: PSH {RA-RD}
0663.0000: FCR @memcmp16+0x2 //061F.0000
0666.0000: MOV A0, A0
0668.0000: POP.NE {PC-DPC}
066B.0000: AND ZERO, A2, 0x1
0670.0000: POP.EQ {PC-DPC}
0673.0000: INC A2, -1
0675.0000: LDB A4, [A3 + A2]
0678.0000: LDB A5, [A1 + A2]
067B.0000: SUB A0, A4, A5
067E.0000: POP {PC-DPC}
@read_line:
0681.0000: MOV A2, A0
0683.0000: MOV A0, ZERO
0685.0000: BRR @read_line+0x13 //0694.0000
0688.0000: INC A0, 1
068A.0000: STB [A2],A3
068C.0000: INC A2, 1
068E.0000: CMP A3, 0xA
0692.0000: RET.EQ
0694.0000: CMP A0, A1
0696.0000: RET.GE
0698.0000: RDB A3, (0)
069A.0000: BRR.LT @read_line+0x7 //0688.0000
069D.0000: XOR A0, 0xFFFF
06A1.0000: RET
06A3.0000: PSH {A1, FP, RA-RD}
06A6.0000: INC FP, SP, 2
06A9.0000: MOV A1, 0x20
06AD.0000: MOV A2, SP
06AF.0000: MOV A3, 0x2
06B3.0000: FCR @gimli_hash
06B6.0000: MOV SP, FP
06B8.0000: POP {FP, PC-DPC}
@some_func2:
06BB.0000: PSH {FP, RA-RD}
06BE.0000: MOV FP, SP
06C0.0000: MOV A1, 0x6874
06C4.0000: MOV A2, 0x5F33
06C8.0000: PSH {A1-A2}
06CB.0000: ADD A0, PC, 0x330
06D0.0000: MOV A1, SP
06D2.0000: MOV A2, 0x4
06D6.0000: FCR @gimli_absorb
06D9.0000: MOV SP, FP
06DB.0000: POP {FP, PC-DPC}
@some_func1:
06DE.0000: PSH {S0-S1, FP, RA-RD}
06E1.0000: INC FP, SP, 4
06E4.0000: ADD S0, PC, 0x317
06E9.0000: MOV A0, S0
06EB.0000: FCR @gimli_hash_init
06EE.0000: MOV A0, S0
06F0.0000: MOV A2, 0x7B6E
06F4.0000: MOV A1, 0x7573
06F8.0000: PSH {A1-A2}
06FB.0000: MOV A1, SP
06FD.0000: MOV A2, 0x4
0701.0000: FCR @gimli_absorb
0704.0000: INC SP, 4
0706.0000: FCR @read_line+0x3a //06BB.0000
0709.0000: MOV A0, S0
070B.0000: ADD A1, PC, 0x235
0710.0000: MOV A2, 0x5
0714.0000: FCR @gimli_absorb
0717.0000: ADD S1, PC, 0x338
071C.0000: LDB A1, [S1]
071E.0000: SHL A1, 0x9
0721.0000: BRR.LT @read_line+0xb3 //0734.0000
0724.0000: SRU A1, 0x9
0727.0000: INC S1, 1
0729.0000: MOV A0, S0
072B.0000: FCR @gimli_absorb_byte
072E.0000: FCR @gimli_advance
0731.0000: BRR @read_line+0x9b //071C.0000
0734.0000: RDC A3, INSN_COUNT_LO
0736.0000: RDC A4, INSN_COUNT_HI
0738.0000: ADD A3, 0x280F
073C.0000: ADD A4, 0x7D52
0740.0000: PSH {A3-A4}
0743.0000: MOV A0, S0
0745.0000: MOV A1, SP
0747.0000: MOV A2, 0x4
074B.0000: FCR @gimli_absorb
074E.0000: INC SP, 4
0750.0000: MOV A0, S0
0752.0000: ADD A1, PC, 0x2DC
0757.0000: MOV A2, 0x20
075B.0000: FCR @gimli_hash_final
075E.0000: INC SP, FP, -4
0761.0000: POP {S0-S1, FP, PC-DPC}
@main:
0764.0000: PSH {S0, FP, RA-RD}
0767.0000: INC FP, SP, 2
076A.0000: SUB SP, 0x52
076E.0000: FCR @read_line+0x5d //06DE.0000
0771.0000: MOV S0, ZERO
0773.0000: ADD A0, PC, 0x188
0778.0000: FCR @puts
077B.0000: MOV A0, SP
077D.0000: MOV A1, 0x32
0781.0000: FCR @read_line
0784.0000: INC A0, -1
0786.0000: WRB.NG (0), 0xA
078A.0000: MOV.NG A0, 0x1
078F.0000: FCR.NG 0xFF00
0793.0000: CMP A0, 0x6
0797.0000: BRR.NE @main+0x68 //07CC.0000
079A.0000: MOV A1, SP
079C.0000: POP A1, {A2-A4}
07A0.0000: CMP A2, 0x6F66
07A4.0000: CMP.EQ A3, 0x6772
07A8.0000: CMP.EQ A4, 0x746F
07AC.0000: BRR.NE @main+0x68 //07CC.0000
07AF.0000: ADD A0, PC, 0x1D4
07B4.0000: FCR @puts
07B7.0000: ADD A0, PC, 0x277
07BC.0000: MOV A1, 0x20
07C0.0000: FCR @print_hex
07C3.0000: WRB (0), 0x22
07C6.0000: WRB (0), 0xA
07C9.0000: BRR @main+0xf //0773.0000
07CC.0000: MOV A3, A0
07CE.0000: SUB A0, FP, 0x22
07D3.0000: MOV A1, 0x20
07D7.0000: MOV A2, SP
07D9.0000: FCR @gimli_hash
07DC.0000: SUB A0, FP, 0x22
07E1.0000: ADD A1, PC, 0x24D
07E6.0000: MOV A2, 0x20
07EA.0000: FCR @memcmp
07ED.0000: CMP A0, ZERO
07EF.0000: BRR.NE @main+0x99 //07FD.0000
07F2.0000: ADD A0, PC, 0x1AC
07F7.0000: FCR @puts
07FA.0000: BRR @main+0xb5 //0819.0000
07FD.0000: ADD A0, PC, 0x11C
0802.0000: FCR @puts
0805.0000: INC S0, 1
0807.0000: CMP S0, 0x3
080B.0000: BRR.LT @main+0xf //0773.0000
080E.0000: ADD A0, PC, 0x137
0813.0000: FCR @puts
0816.0000: BRR @main+0xf //0773.0000
0819.0000: MOV A0, ZERO
081B.0000: INC SP, FP, -2
081E.0000: POP {S0, FP, PC-DPC}
0821.0000: STW [FP],FP
0823.0000: BRR @main
There is a hash function named gimli. The process is implemented in @gimli_hash:
- call @gimli_hash_init
- call @gimli_absorb
- call @gimli_hash_final
The program computes the hash of flag and compares it to the hash of the user's input. To bypass this, we recover the secret by reverse-engineering the hashing process in some_func1, which initializes the hash with @gimli_hash_init and absorbs data using @gimli_absorb and related functions. Initially, attempting to set a breakpoint on @gimli_absorb missed the individual bytes absorbed via @gimli_absorb_byte.
Therefore, we use the debugger to find the A1 parameter of @gimli_absorb_byte, byte by byte:
$ ./runpeg --debug AccessCode.peg
EAR debugger
(dbg) b 04e9
Created breakpoint #1 at address 04E9 (X)
(dbg) c
HW breakpoint #1 hit trying to execute 1 byte at 04E9
A breakpoint was hit
Thread state:
(ZERO)R0: 0000 (S1)R8: FD97
(A0)R1: 0A00 (S2)R9: 0004
(A1)R2: 0073 (FP)R10: FD90
(A2)R3: 0004 (SP)R11: FD8A
(A3)R4: 0000 (RA)R12: 053B
(A4)R5: 0000 (RD)R13: 0000
(A5)R6: EA23 (PC)R14: 04E9 //@gimli_absorb_byte+0
(S0)R7: 0A00 (DPC)R15: 0000
FLAGS: zspcvXr
Next instructions:
@gimli_absorb_byte:
04E9.0000: LDW A2, [A0 + 0x30]
04EE.0000: ADD A2, A0
04F0.0000: LDB A3, [A2]
04F2.0000: XOR A3, A1
04F4.0000: STB [A2],A3
(dbg) c
HW breakpoint #1 hit trying to execute 1 byte at 04E9
A breakpoint was hit
Thread state:
(ZERO)R0: 0000 (S1)R8: FD98
(A0)R1: 0A00 (S2)R9: 0003
(A1)R2: 0075 (FP)R10: FD90
(A2)R3: 0001 (SP)R11: FD8A
(A3)R4: 0073 (RA)R12: 053B
(A4)R5: 0000 (RD)R13: 0000
(A5)R6: EA23 (PC)R14: 04E9 //@gimli_absorb_byte+0
(S0)R7: 0A00 (DPC)R15: 0000
FLAGS: zspcvXr
Next instructions:
@gimli_absorb_byte:
04E9.0000: LDW A2, [A0 + 0x30]
04EE.0000: ADD A2, A0
04F0.0000: LDB A3, [A2]
04F2.0000: XOR A3, A1
04F4.0000: STB [A2],A3
(dbg) c
HW breakpoint #1 hit trying to execute 1 byte at 04E9
A breakpoint was hit
Thread state:
(ZERO)R0: 0000 (S1)R8: FD99
(A0)R1: 0A00 (S2)R9: 0002
(A1)R2: 006E (FP)R10: FD90
(A2)R3: 0002 (SP)R11: FD8A
(A3)R4: 0075 (RA)R12: 053B
(A4)R5: 0000 (RD)R13: 0000
(A5)R6: EA23 (PC)R14: 04E9 //@gimli_absorb_byte+0
(S0)R7: 0A00 (DPC)R15: 0000
FLAGS: zspcvXr
Next instructions:
@gimli_absorb_byte:
04E9.0000: LDW A2, [A0 + 0x30]
04EE.0000: ADD A2, A0
04F0.0000: LDB A3, [A2]
04F2.0000: XOR A3, A1
04F4.0000: STB [A2],A3
Converting the values of A1 (in hex) to ASCII yields:
>>> bytes.fromhex("73756e")
b'sun'
By repeatedly stepping through the debugger and collecting the A1 values, we recover the flag: sun{th3_fun_p4r7_15_nEAR}.