From 9939378130ec5572e0f957d16cfb5f1cbc132199 Mon Sep 17 00:00:00 2001
From: h7x4 <h7x4@nani.wtf>
Date: Sat, 4 Jul 2026 19:24:40 +0900
Subject: [PATCH] crypto/shared_secrets

---
 crypto/shared_secrets/encryption.py | 30 +++++++++++++++++++++++++++++
 crypto/shared_secrets/message.txt   |  5 +++++
 crypto/shared_secrets/solve.py      | 13 +++++++++++++
 3 files changed, 48 insertions(+)
 create mode 100644 crypto/shared_secrets/encryption.py
 create mode 100644 crypto/shared_secrets/message.txt
 create mode 100755 crypto/shared_secrets/solve.py

diff --git a/crypto/shared_secrets/encryption.py b/crypto/shared_secrets/encryption.py
new file mode 100644
index 0000000..7ecbc0e
--- /dev/null
+++ b/crypto/shared_secrets/encryption.py
@@ -0,0 +1,30 @@
+from Crypto.Util.number import getPrime
+from random import randint
+
+# Public parameters
+g = 2
+p = getPrime(1048)
+
+# Server's secret
+a = randint(2, p-2)
+A = pow(g, a, p)
+
+# Client secret
+b = '???'  
+
+B = pow(g, b, p)
+
+# Shared key
+shared = pow(A, b, p)
+
+# Encrypt flag
+flag = b"picoCTF{...}"
+enc = bytes([x ^ (shared % 256) for x in flag])
+
+# Write challenge info
+with open("file.txt", "w") as f:
+    f.write(f"g = {g}\n")
+    f.write(f"p = {p}\n")
+    f.write(f"A = {A}\n")
+    f.write(f"b = {b} \n")
+    f.write(f"enc = {enc.hex()}\n")
diff --git a/crypto/shared_secrets/message.txt b/crypto/shared_secrets/message.txt
new file mode 100644
index 0000000..c68b4e9
--- /dev/null
+++ b/crypto/shared_secrets/message.txt
@@ -0,0 +1,5 @@
+g = 2
+p = 2353855297163603230718659874235969189211904801854831749272164556125452734594903161934794163403497762726605985627409234420965176613218858624400366466853770681834062810872998733968827992223178685800438220675248064587881077258421057484096470778462916510705650691145000008812988897851274637295629476960165825128891910793
+A = 30068494220298681891330724690865821714005524540061986470484739235070782982875821399659951687122702703103707881496322805008910484300535488856317760253374747778591137899431437661178126794196697625682849937450966265318752778435469929326325997632296225043026449906879570022308070668814741550246868893784772044251768510
+b = 2252298426168643058908675994457951125000150972241848576912471697630407791150123415344081881294633730616725212738161375429295138914772118107750191302567546774258844274932453145325172167340764005882111243473134993891638369747707408050760320040529699904616084248365714753162172475940998916650267854128138430013641052250
+enc = 839a909cb0a7b588979bac80c09081c087acc291c1c696c2ca958e
diff --git a/crypto/shared_secrets/solve.py b/crypto/shared_secrets/solve.py
new file mode 100755
index 0000000..8760bc2
--- /dev/null
+++ b/crypto/shared_secrets/solve.py
@@ -0,0 +1,13 @@
+#!/usr/bin/env python3
+
+g = 2
+p = 2353855297163603230718659874235969189211904801854831749272164556125452734594903161934794163403497762726605985627409234420965176613218858624400366466853770681834062810872998733968827992223178685800438220675248064587881077258421057484096470778462916510705650691145000008812988897851274637295629476960165825128891910793
+A = 30068494220298681891330724690865821714005524540061986470484739235070782982875821399659951687122702703103707881496322805008910484300535488856317760253374747778591137899431437661178126794196697625682849937450966265318752778435469929326325997632296225043026449906879570022308070668814741550246868893784772044251768510
+b = 2252298426168643058908675994457951125000150972241848576912471697630407791150123415344081881294633730616725212738161375429295138914772118107750191302567546774258844274932453145325172167340764005882111243473134993891638369747707408050760320040529699904616084248365714753162172475940998916650267854128138430013641052250
+enc = "839a909cb0a7b588979bac80c09081c087acc291c1c696c2ca958e"
+
+shared = pow(A, b, p)
+
+enc_bytes = [int(enc[i:i+2], 16) for i in range(0, len(enc), 2)]
+flag = bytes([x ^ (shared % 256) for x in enc_bytes])
+print(flag.decode())