Question

secret_phase

Asked by: SirakMD

I read most of the explanation  that infinity08 gave to others and it helped me a lot to figure out the previous phases. thanks  a lot for your effort and willingness.
Now I'm trying to figure out how i can get the secret phase.
1) here i couldn't figure out where the %eax value coming from.
2)how can make it not jump here
804923a:      83 f8 02                   cmp    $0x2,%eax
 804923d:      75 31                      jne    8049270 <phase_defused+0x74>
3) there is also another jump that should not be made, i couldn't figure out where the sscanf gets its inputs
804924f:      85 c0                      test   %eax,%eax
 8049251:      75 1d                      jne    8049270 <phase_defused+0x74>
4)where should i enter the input string, i tried at the end after after the 6th phase is diffused, didn't work and also how would that be read
5)or is it next to the answer in another phase, if so where would i to try ?

Here is the defused_phase code

080491fc <phase_defused>:
 80491fc:      55                         push   %ebp
 80491fd:      89 e5                      mov    %esp,%ebp
 80491ff:      53                         push   %ebx
 8049200:      83 ec 74                   sub    $0x74,%esp
 8049203:      c7 04 24 01 00 00 00       movl   $0x1,(%esp)
 804920a:      e8 a0 fd ff ff             call   8048faf <send_msg>
 804920f:      83 3d 2c a8 04 08 06       cmpl   $0x6,0x804a82c
 8049216:      75 70                      jne    8049288 <phase_defused+0x8c>
 8049218:      8d 5d ac                   lea    0xffffffac(%ebp),%ebx
 804921b:      89 5c 24 0c                mov    %ebx,0xc(%esp)
 804921f:      8d 45 a8                   lea    0xffffffa8(%ebp),%eax
 8049222:      89 44 24 08                mov    %eax,0x8(%esp)
 8049226:      c7 44 24 04 86 9a 04       movl   $0x8049a86,0x4(%esp)
 804922d:      08
 804922e:      c7 04 24 30 a9 04 08       movl   $0x804a930,(%esp)
 8049235:      e8 b2 f6 ff ff             call   80488ec <sscanf@plt>
 804923a:      83 f8 02                   cmp    $0x2,%eax
 804923d:      75 31                      jne    8049270 <phase_defused+0x74>
 804923f:      c7 44 24 04 8c 9a 04       movl   $0x8049a8c,0x4(%esp)
 8049246:      08
 8049247:      89 1c 24                   mov    %ebx,(%esp)
 804924a:      e8 ff fc ff ff             call   8048f4e <strings_not_equal>
 804924f:      85 c0                      test   %eax,%eax
 8049251:      75 1d                      jne    8049270 <phase_defused+0x74>
 8049253:      c7 04 24 08 9c 04 08       movl   $0x8049c08,(%esp)
 804925a:      e8 cd f5 ff ff             call   804882c <puts@plt>
 804925f:      c7 04 24 30 9c 04 08       movl   $0x8049c30,(%esp)
 8049266:      e8 c1 f5 ff ff             call   804882c <puts@plt>
 804926b:      e8 29 fa ff ff             call   8048c99 <secret_phase>
 8049270:      c7 04 24 68 9c 04 08       movl   $0x8049c68,(%esp)
 8049277:      e8 b0 f5 ff ff             call   804882c <puts@plt>
 804927c:      c7 04 24 94 9c 04 08       movl   $0x8049c94,(%esp)
 8049283:      e8 a4 f5 ff ff             call   804882c <puts@plt>
 8049288:      83 c4 74                   add    $0x74,%esp
 804928b:      5b                         pop    %ebx
 804928c:      5d                         pop    %ebp
 804928d:      c3                         ret    

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Asked On
2009-11-05 at 18:56:48ID24876879
Tags

assembly prog.

Topics

Assembly Programming Language

,

Development Software

,

OS / 2 Software

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Answers

 

by: Infinity08Posted on 2009-11-06 at 08:12:29ID: 25760393

>> 1) here i couldn't figure out where the %eax value coming from.

>>  8049235:      e8 b2 f6 ff ff             call   80488ec <sscanf@plt>
>>  804923a:      83 f8 02                   cmp    $0x2,%eax

eax contains the return value of sscanf, ie. the amount of successfully read items :

        http://www.cplusplus.com/reference/clibrary/cstdio/sscanf/


>> 2)how can make it not jump here

The string passed to sscanf needs to be such that sscanf returns the expected value.


>> i couldn't figure out where the sscanf gets its inputs

They are put on the stack before calling sscanf :

>>  8049218:      8d 5d ac                   lea    0xffffffac(%ebp),%ebx
>>  804921b:      89 5c 24 0c                mov    %ebx,0xc(%esp)
>>  804921f:      8d 45 a8                   lea    0xffffffa8(%ebp),%eax
>>  8049222:      89 44 24 08                mov    %eax,0x8(%esp)
>>  8049226:      c7 44 24 04 86 9a 04       movl   $0x8049a86,0x4(%esp)
>>  804922d:      08
>>  804922e:      c7 04 24 30 a9 04 08       movl   $0x804a930,(%esp)


>> 4)where should i enter the input string, i tried at the end after after the 6th phase is diffused, didn't work and also how would that be read

The string sscanf works with is located at address 0x804a930 ... you'll have to check the rest of the code to see where that string is filled.

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