From 2e15bb28bca4e0976e339158b69132ff99290a4b Mon Sep 17 00:00:00 2001
From: Vivian Dai <38384400+vivian-dai@users.noreply.github.com>
Date: Tue, 7 Sep 2021 13:15:56 -0400
Subject: [PATCH 1/2] Added My Friend John - Miscellaneous

---
 Miscellaneous/My Friend John/MyFriendJohn.zip | Bin 0 -> 1331 bytes
 Miscellaneous/My Friend John/README.md        |  21 ++++++++++++++++++
 2 files changed, 21 insertions(+)
 create mode 100644 Miscellaneous/My Friend John/MyFriendJohn.zip
 create mode 100644 Miscellaneous/My Friend John/README.md

diff --git a/Miscellaneous/My Friend John/MyFriendJohn.zip b/Miscellaneous/My Friend John/MyFriendJohn.zip
new file mode 100644
index 0000000000000000000000000000000000000000..81219eb79f1e5d0d15dcdf6228baf64b29efd257
GIT binary patch
literal 1331
zcmWIWW@h1H0D(K*=Y!%BCdAdVFff2HKZ6WIX>qD<QGRlEWqzq%Rc1kG2qy!xfXvAR
z5H79YW?*D_!OXzG@)Ae{01Xmh;AG%nnACATXy5(6vF?lv3=&KbgOW>&OY(Ddb25ud
z^hzp9zy>`QJ(&Q)Xa*T&7f5_@4rF=7w^pY(`*7YFZPf!AHtWh|XT0<BXV%rO>HoQP
z!PDkCyANfI>)5j+{<pA29XrCwa(vVEj9)LA^FH#(8Zj3ner|0x(bh1wxRTYG-)kJV
zuJLL60yeGown-lYxIaCxG}+B`T>hO`+^o~5*X18Kzt&Txc6s{B=TkPn?e#t~A^ZK*
zhTjU0!#v!2|DQXs_ddhCMY9&0x-su9_p!NX^(a0hF3qiceQNnKi)uw~-Mn|6KO7fX
znOWFusEyd)JfVuWylUU8D^G5f&0VM?Tc3ZkI{tFyf;AUxBkbS4maWL)RFS(pBlDQh
z>hr2E!&T>%PW`mMU{21@WQRC8_VUFgJR8d|Fz`+;c;jh#RrnHvt%Ido^hNEuty%5C
zYv%?zRcSWc-t}H}>wM(0_m>N&T<{mxIQFcv;(|cs_U_MrzUU>1`<y$zy(GY!odY=*
zK=H!`j2{Muo1N!_lv#hxJqC=QT|f+qXyo{TMYN~H$pjEai=WK2Ip=On)Gv^zXlkB!
z;L>ejuRq3%GGCo)^c1^dvWKg56{Az&A^lmF6OY<nZC9D!DDz7r=kY342JQGoYQMt6
zxOwKN1qXXC4cg*vTXyz{)^(i?T(VD8rp?(iOXhO}7dL0{HK8S?rZLB_cd?rBTdOGj
zm6G9gIk~F#l7h3d^zzw;wL0BxX9UkDb6l?G=DdGa@__k%k+^Ny4$1=C*#$daCd)|6
z?+RL>AtN5NRe9y^_q)A!>^h~Vw$9Z#?r`nhy!*+P3cQ^&-^}>Nen@Et@9DU5!G%Ws
z4EHXJfBM_Fg=MN#PCt(`hw#UbE*z{s+<%p^1}Jt186{n+y0*K<;P}27|FleGw?$Q5
zI}u>|ZJEc<)xokZK6f%AvJV9=ER|hu6l@SF&bTl1!_zBfJPOk`ylQc2(Tkt{W7;N-
z+rk#>*WFnxbv(P*uAJprYnI^G1;W3@KkrIBn<?#`n2~v=Z}k_Ic_MYii>w=1yg9C9
z$Cv&2x6L8;>FFbG+y4H1nNZEo7a6WF@zVWuQ+{-?gddqboi}lc-}5(Tr~5RBoQ~4?
z-<#fNBD1}C>E4wBd}sE@&$^VGc}n@<rgqNTc|Q+$iT>0!_~LD)_BQ&I;mOOO<bj+B
z0=yZS<d|_~U<q&u0Zc0lOBz8;<m3X*&a4c~Sh6z2P+X}FVkpSCC5;P!W+NL4PJ=*0
zv82BMZ&o&tCMF<U1*G=_3m;JN19CsEk__1@kZO!_4QLhCG7VxCBLgEtC{Wu8V6n)+
F003aj^G*N&

literal 0
HcmV?d00001

diff --git a/Miscellaneous/My Friend John/README.md b/Miscellaneous/My Friend John/README.md
new file mode 100644
index 0000000..cff54aa
--- /dev/null
+++ b/Miscellaneous/My Friend John/README.md	
@@ -0,0 +1,21 @@
+## My Friend John
+The main idea is learning how to use tools for cracking password protected zip files.
+
+#### Step-1:
+We can open [`MyFriendJohn.zip`](./MyFriendJohn.zip) using [7zip](https://www.7-zip.org/) and extract `use-rockyou.zip`.
+
+#### Step-2:
+Now we need a password to open `use-rockyou.zip`. There's a really popular wordlist called rockyou which can be downloaded [here](https://github.com/brannondorsey/naive-hashcat/releases/download/data/rockyou.txt).
+
+#### Step-3:
+We can use [fcrackzip](https://github.com/hyc/fcrackzip)'s dictionary attack: `fcrackzip -v -u -D -p rockyou.txt use-rockyou.zip` using rockyou.
+
+#### Step-4:
+We now see `custom-list.txt` and `custom-list.zip`. We can use the custom word list to unlock the the zip file: `fcrackzip -v -u -D -p custom-list.txt custom-list.zip`.
+
+#### Step-5:
+The last zip file is called `brute-force-pin.zip`. A pin is usually between 4 and 6 numeric digits. `fcrackzip -b -c "1" -l 4-6 -v -u brute-force-pin.zip`. The `-c "1"` means only use numeric digits when bruteforcing.
+
+#### Step-6:
+Finally we get a `flag.txt` and the flag becomes:
+`CTFlearn{s0_n0W_y0uv3_M3t_J0hN}`
\ No newline at end of file

From aeafa926b1ee2a8b25ffff1f3deb50be7883baa9 Mon Sep 17 00:00:00 2001
From: Vivian Dai <38384400+vivian-dai@users.noreply.github.com>
Date: Sat, 11 Dec 2021 12:53:29 -0500
Subject: [PATCH 2/2] Added The Credit Card Fraudster - Programming

---
 .../The Credit Card Fraudster/README.md       | 17 ++++++++++++
 .../The Credit Card Fraudster/solve.py        | 27 +++++++++++++++++++
 2 files changed, 44 insertions(+)
 create mode 100644 Programming/The Credit Card Fraudster/README.md
 create mode 100644 Programming/The Credit Card Fraudster/solve.py

diff --git a/Programming/The Credit Card Fraudster/README.md b/Programming/The Credit Card Fraudster/README.md
new file mode 100644
index 0000000..7a98d8c
--- /dev/null
+++ b/Programming/The Credit Card Fraudster/README.md	
@@ -0,0 +1,17 @@
+## The Credit Card Fraudster
+The main idea is checking numbers in a given range against the Luhn algorithm
+
+#### Step-1:
+Implement the Luhn algorithm which works like this:
+1. Start from the least significant (right most) digit
+2. Take the sum of the digits from right to left but double every second digit. If the digit doubled is greater than 10, take the sum of the digits on that doubled value
+3. If the final value can divide evenly into 10, passes the Luhn check, otherwise it does not
+
+#### Step-2:
+Now we need to get the range of numbers that fit the credit card number in the format of `543210******1234`. This would mean all numbers from `5432100000001234` to `5432109999991234` with an increment of `10000`
+
+#### Step-3:
+Loop through all possible numbers, check if it's divisible by `123457` and passes the Luhn check.
+
+#### Step-4:
+The flag is revealed after running the script.
\ No newline at end of file
diff --git a/Programming/The Credit Card Fraudster/solve.py b/Programming/The Credit Card Fraudster/solve.py
new file mode 100644
index 0000000..7c1d92b
--- /dev/null
+++ b/Programming/The Credit Card Fraudster/solve.py	
@@ -0,0 +1,27 @@
+min_val = 5432100000001234
+max_val = 5432109999991234
+inc = 10000
+
+def luhn_check(num):
+    def sum_of_digits(n):
+        s = str(n)
+        t = 0
+        for c in s:
+            t += int(c)
+        return t
+    
+    string = str(num)
+    total = 0
+    double = False
+    for i in range(len(string) - 1, -1, -1):
+        c = string[i]
+        if double:
+            total += int(c)*2 if int(c)*2 < 10 else sum_of_digits(int(c)*2)
+        else:
+            total += int(c)
+        double = not double
+    return total%10 == 0
+
+for i in range(min_val, max_val, inc):
+    if i%123457 == 0 and luhn_check(i):
+        print(i)
\ No newline at end of file