#Defcamp CTF Qualification 2015
##No Crypto (Crypto 200)

The folowing plaintext has been encrypted using an unknown key, with AES-128 CBC:

- Original: Pass: sup3r31337. Don't loose it!
- Encrypted: 4f3a0e1791e8c8e5fefe93f50df4d8061fee884bcc5ea90503b6ac1422bda2b2b7e6a975bfc555f44f7dbcc30aa1fd5e
- IV: 19a9d10c3b155b55982a54439cb05dce

How would you modify it so that it now decrypts to: "Pass: notAs3cre7. Don't loose it!"

This challenge does not have a specific flag format.

####풀이 방법
* 메시지를 바꾸고 싶다는 문제
- Original 메시지와 바꾸려는 메시지의 차이가 첫 블록만 다름
- IV + plaintext를 처음 주어진 문제와 같게 맞추면 암호문이 같아짐

* IV xor Original = IV' xor NewMsg
* IV' = IV xor Original xor NewMsg

Original writeup (https://github.com/tyhan/CTF/blob/master/Defcamp2015/No_Crypto/README.md).