Added signal_party Challenge

README.md

@@ -33,6 +33,7 @@ docker compose down
 |[B4nner](challenges/B4nner)|Linux|Easy|True
 |[B4nner_2](challenges/B4nner_2)|Linux|Medium|True
 |[G0t_A_IO](challenges/G0t_A_IO)|OSINT|Easy|False
+|[signal_party](challenges/signal_party)|Revers|Easy|False
 
 > This table will be updated everytime i add a challenge to the repo
 

challenges/signal_party/README.md

@@ -0,0 +1,20 @@
+# Signal_Party
+
+ - **`Author:`** [SlyPex](https://github.com/SlyPex)
+ - **`CTF:`** [AlphaCTF2K24](https://github.com/Spidey-y/AlphaCTF2k24)
+ - **`Categorie:`** Reverse
+ - **`Difficulty:`** Easy
+
+## Description
+
+>  
+    Me and my friends decided to host a party.
+    It was full of signals.
+
+**Note** : Regex : `AlphaCTF{[^SI023468]+}`.
+
+Wrap the decoded string with AlphaCTF{}.
+
+## Solution
+
+Solution of the challenge can be found [here](solution/).

challenges/signal_party/challenge.yml

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+name: "signal_party"
+author: "SlyPex"
+author_link: "https://github.com/SlyPex"
+
+category: reverse
+
+difficulty: easy
+
+description: |
+  > Me and my friends decided to host a party.
+    It was full of signals.
+    **Note** : Regex : AlphaCTF{[^SI023468]+}.
+    Wrap the decoded string with AlphaCTF{}.
+
+  **Author** : SlyPex
+flags:
+  - AlphaCTF{YOU_R_REALLY_A_519NAL_PLAY9ROUND_MA57ER}
+
+tags:
+  - Reverse
+  - Easy
+
+value: 500
+extra:
+  initial: 500
+  decay: 35
+  minimum: 50
+state: hidden
+version: "0.1"

challenges/signal_party/challenge/chall.c

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+#include<stdio.h>
+#include<stdlib.h>
+#include<signal.h>
+#include<unistd.h>
+#include<sys/types.h>
+
+FILE *output;
+
+void encrypt(int sig){
+  fputc(sig + 0x7F, output);
+}
+
+int main (int argc, char *argv[])
+{
+  pid_t pid = getpid();
+  char c;
+  FILE *flag = fopen("flag.txt","r");
+  if ( flag == NULL ){
+    printf("Could not open file.\n");
+    return 1;
+  }
+  output = fopen("output","w");
+
+  signal(SIGSYS,encrypt);
+  signal(SIGPOLL,encrypt);
+  signal(SIGWINCH,encrypt);
+  signal(SIGVTALRM,encrypt);
+  signal(SIGXCPU,encrypt);
+  signal(SIGTTOU,encrypt);
+  signal(SIGTSTP,encrypt);
+  signal(SIGCHLD,encrypt);
+  signal(SIGTERM,encrypt);
+  signal(SIGPIPE,encrypt);
+  signal(SIGSEGV,encrypt);
+  signal(SIGFPE,encrypt);
+  signal(SIGABRT,encrypt);
+  signal(SIGILL,encrypt);
+  signal(SIGINT,encrypt);
+  signal(SIGHUP,encrypt);
+  signal(SIGQUIT,encrypt);
+  signal(SIGTRAP,encrypt);
+  signal(SIGBUS,encrypt);
+  signal(SIGUSR1,encrypt);
+  signal(SIGUSR2,encrypt);
+  signal(SIGALRM,encrypt);
+  signal(SIGSTKFLT,encrypt);
+  signal(SIGCONT,encrypt);
+  signal(SIGTTIN,encrypt);
+  signal(SIGURG,encrypt);
+  signal(SIGXFSZ,encrypt);
+  signal(SIGPROF,encrypt);
+  signal(SIGIO,encrypt);
+  signal(SIGPWR,encrypt);
+
+  while ((c = fgetc(flag))!= EOF)
+  {
+    if ((int)c > 64 )
+    {
+      kill(pid,(int)c % 32);
+    }else if((int)c < 58){
+      kill(pid,(int)c % 32 % 5 + 27);
+    }
+  }
+
+  fclose(flag);
+  fclose(output);
+
+  return 0;
+}

challenges/signal_party/challenge/flag.txt

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+YOU_R_REALLY_A_519NAL_PLAY9ROUND_MA57ER

challenges/signal_party/challenge/output

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+����������������������������������������

challenges/signal_party/solution/README.md

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+# Signal_Party
+
+## Write-up
+
+> i'll probably change this write-up
+
+You only have to reverse the binary, and using the extra information given in the challenge description we get this :
+
+```python
+from string import ascii_uppercase,digits
+
+# Possible Charcters For The Flag : AlphaCTF{[^SI023468]+}.
+letters = ascii_uppercase + digits + '_'
+# Removing non-included letters
+letters = [letter for letter in letters if letter not in 'SI023468']
+
+# Building the dictionary where each letter from letters list matches its encrypted value
+transformer = {}
+for letter in letters:
+    if ord(letter) > 64:
+        transformer[ord(letter) % 32] = letter
+    elif ord(letter) < 58:
+        transformer[(ord(letter) % 32)% 5 + 27] = letter
+
+# Getting the values of the Encrypted chars [output file].
+f = open("output", "rb")
+encoded_flag = f.read()[:-1] # Remove the new line char 
+flag = 'AlphaCTF{'
+
+for char in encoded_flag:
+    flag += transformer[char - 0x7F]
+
+flag += '}'
+print(flag)
+```
+
+## Flag
+`AlphaCTF{YOU_R_REALLY_A_519NAL_PLAY9ROUND_MA57ER}`

challenges/signal_party/solution/output

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+����������������������������������������

challenges/signal_party/solution/sol.py

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+from string import ascii_uppercase,digits
+
+# Possible Charcters For The Flag : AlphaCTF{[^SI023468]+}.
+letters = ascii_uppercase + digits + '_'
+# Removing non-included letters
+letters = [letter for letter in letters if letter not in 'SI023468']
+
+# Building the dictionary where each letter from letters list matches its encrypted value
+transformer = {}
+for letter in letters:
+    if ord(letter) > 64:
+        transformer[ord(letter) % 32] = letter
+    elif ord(letter) < 58:
+        transformer[(ord(letter) % 32)% 5 + 27] = letter
+
+# Getting the values of the Encrypted chars [output file].
+f = open("output", "rb")
+encoded_flag = f.read()[:-1] # Remove the new line char 
+flag = 'AlphaCTF{'
+
+for char in encoded_flag:
+    flag += transformer[char - 0x7F]
+
+flag += '}'
+print(flag)