Rating: 5.0

# Reversing: core
Given core dump of executable ./run and the source code run.c.
First guess we need to find the flag from the memory, since the app crashed and core dump collected.
## Static Analysis
Analyzing the core:

core: ELF 64-bit LSB core file, x86-64, version 1 (SYSV), SVR4-style, from './run', real uid: 1000, effective uid: 1000, real gid: 1000, effective gid: 1000, execfn: './run', platform: 'x86_64'


Reading the run.c found interesting function:
c
void xor(char *str, int len) {
for (int i = 0; i < len; i++) {
str[i] = str[i] ^ 1;
}
}

## Solution
1. We can find the flag by searching the core binary data, since we already know the flag must be stored in the XORed by 1 in the memory
1. Spin some debugger to load the core dump file

I choose the first solution.

Since we already know the flag always be started by TUCTF{ we can use this data as signature to search entire core dump file. Don't fortget to perform XOR to the signature data.

54 55 43 54 46 7b XORed by 01 01 01 01 01 01

result = 55 54 42 55 47 7a

Now we can find this data in core dump file:

shell
Admin@sybond-MBP TUCTF % hexdump -C core | grep "55 54 42 55 47 7a"
00006040 55 54 42 55 47 7a 62 31 73 32 5e 65 74 6c 71 3e |UTBUGzb1s2^etlq>|
Admin@sybond-MBP TUCTF % hexdump -C core | grep 000060
00000060 1c 0e 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
00000600 fc 7f 00 00 00 00 00 00 00 00 00 00 ff ff ff ff |................|
00006000 00 00 00 00 00 00 00 00 08 c0 a5 e3 25 56 00 00 |............%V..|
00006010 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
00006020 a0 06 2e 57 68 7f 00 00 00 00 00 00 00 00 00 00 |...Wh...........|
00006030 80 f9 2d 57 68 7f 00 00 00 00 00 00 00 00 00 00 |..-Wh...........|
00006040 55 54 42 55 47 7a 62 31 73 32 5e 65 74 6c 71 3e |UTBUGzb1s2^etlq>|
00006050 5e 4f 32 77 32 73 5e 69 32 35 73 65 5e 31 67 5e |^O2w2s^i25se^1g^|
00006060 78 31 74 7c 0b 00 00 00 00 00 00 00 00 00 00 00 |x1t|............|
00006070 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|



after XOR with 0x01 result 54 55 43 54 46 7b 63 30 72 33 5f 64 75 6d 70 3f 5f 4e 33 76 33 72 5f 68 33 34 72 64 5f 30 66 5f 79 30 75 7d. Or in other presentation (text):