Being terrible at assembly and reversing, I stumbled through this but still gotthe flag. First, I downloaded the provided binary and loaded it in[Binary Ninja](https://binary.ninja/). Looking at the graph, I could see thatthe "decrypted" flag is stored is a `flag_buf` variable at `0x6013e8` and thatthe `decrypt_flag` function returns at `0x4008c8`.
With that information, we can fire up dbg :
```bashgdb run```
Then set up a break point at `0x4008c8` and execute until we reach thebreakpoint :
```break *0x4008c8run```
Once the breakpoint is reached, we read the string stored at `0x6013e8` :
```x/s *0x6013e8```
And that gives us the flag : `picoCTF{gDb_iS_sUp3r_u53fuL_efaa2b29}`