Alice wants to send you her secret flag and asks you to generate a shared secret with her. She also tells you she will be using the NIST standard:

g: 2
p: 2410312426921032588552076022197566074856950548502459942654116941958108831682612228890093858261341614673227141477904012196503648957050582631942730706805009223062734745341073406696246014589361659774041027169249453200378729434170325843778659198143763193776859869524088940195577346119843545301547043747207749969763750084308926339295559968882457872412993810129130294592999947926365264059284647209730384947211681434464714438488520940127459844288859336526896320919633919

You receive the following integer from Alice:



A: 112218739139542908880564359534373424013016249772931962692237907571990334483528877513809272625610512061159061737608547288558662879685086684299624481742865016924065000555267977830144740364467977206555914781236397216033805882207640219686011643468275165718132888489024688846101943642459655423609111976363316080620471928236879737944217503462265615774774318986375878440978819238346077908864116156831874695817477772477121232820827728424890845769152726027520772901423784

You then generate your secret integer and calculate your public one, which you send to Alice.

b: 197395083814907028991785772714920885908249341925650951555219049411298436217190605190824934787336279228785809783531814507661385111220639329358048196339626065676869119737979175531770768861808581110311903548567424039264485661330995221907803300824165469977099494284722831845653985392791480264712091293580274947132480402319812110462641143884577706335859190668240694680261160210609506891842793868297672619625924001403035676872189455767944077542198064499486164431451944
B: 1241972460522075344783337556660700537760331108332735677863862813666578639518899293226399921252049655031563612905395145236854443334774555982204857895716383215705498970395379526698761468932147200650513626028263449605755661189525521343142979265044068409405667549241125597387173006460145379759986272191990675988873894208956851773331039747840312455221354589910726982819203421992729738296452820365553759182547255998984882158393688119629609067647494762616719047466973581

Individually you each use the shared secret to derive an AES private key. This allows you to encrypt large amounts of data over your channel without needing to exchange keys again.

Alice sends you the following IV and ciphertext:

{'iv': '737561146ff8194f45290f5766ed6aba', 'encrypted_flag': '39c99bf2f0c14678d6a5416faef954b5893c316fc3c48622ba1fd6a9fe85f3dc72a29c394cf4bc8aff6a7b21cae8e12c'}

Decrypt this to obtain your flag!

The decrypt.py script is provided to help you here and on future challenges too.

Challenge files:
  - source.py
  - decrypt.py