Reverse Engineering
{"authors": ["ret2basic"]}

not crypto

Solved by ret2basic

Challenge

there's crypto in here but the challenge is not crypto... πŸ€”
​not-crypto​

Solution

The program calls memcmp() for comparing our input with the flag:
memcmp()
The address of memcmp() is 0x13b9:
Address of memcmp()
Since PIE is enabled, this address is only an offset. Now we find the base address of the binary:
PIE base address
Set a breakpoint at 0x555555554000 + 0x13b9 = 0x5555555553b9 and read the flag:
Get flag

breadth

Solved by ret2basic

Challenge

Surely this is what people mean when they say "horizontal scaling," right?

TOP SECRET INFO:

Our operatives managed to exfiltrate an in-development version of this challenge, where the function with the real flag had a mistake in it. Can you help us get the flag?

Solution

Compare these two binaries and examine which bytes are different:
cmp -bl breadth.v1 breadth.v2
cmp
Here 610380 refers to the function located at address 0x9504C. Examine this function in IDA:
Function
Get flag:
Get flag
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Outline
not crypto
Challenge
Solution
breadth
Challenge
TOP SECRET INFO:
Solution