CCE2023 APOLLO CRYPTO [100] - Base64?

Description

커스텀 키 테이블을 이용한 base64

 

user.tar

0.01MB

encode_flag.txt
7nqRmsVR7AD/mhOpmsyNnHyp7YO+mHORmHOAnHDpihFl95==

data.txt
How many special people change? How many lives are livin' strange? Where were you while we were getting high? Slowly walkin' down the hall Faster than a cannonball Where were you while we were getting high? Someday you will find me Caught beneath the landslide In a champagne supernova in the sky Someday you will find me Caught beneath the landslide In a champagne supernova A champagne supernova in the sky Wake up the dawn and ask her why A dreamer dreams she never dies Wipe that tear away now from your eye Slowly walkin' down the ha11 Faster than a cannonball Where were you while we were getting high?

encode_data.txt
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

 

풀이법 1

data와 encode_data를 가지고 base64로 변환하여 key를 획득한다.

이후 encode_flag와 매핑하여 flag로 복호화

fd = open("data.txt", 'r')   # plain text
fe = open("encode_data.txt", 'r')  # encrypted text by base64
ef = open("encode_flag.txt")  # encrypted flag

data = fd.readline()
encode_data = fe.readline()
encode_flag = ef.readline()

binaryData = "" # 2진수 데이터
b64_dict = {}

# plain text를 2진수로 변환한다.
for i in range(len(data)):
    tmpData = bin(ord(data[i]))[2:]
    filledTmpData = tmpData.zfill(8) # 2진수 변환 및 0으로 채움
    binaryData += str(filledTmpData) # String으로 형변환

for i in range(len(binaryData)):
    if i % 6 == 5:
        b64_dict[encode_data[i // 6]] = binaryData[i - 5:i + 1:]

def dec_flag(df):
    flag = ""
    for i in range(0, len(df), 8):
        flag += chr(int(df[i:i + 8:], 2))
    print(flag)


decode_flag = ""
for i in range(len(encode_flag)):
    decode_flag += b64_dict[encode_flag[i]]
    dec_flag(decode_flag[:])

 

 

풀이법 2

# 데이터를 스트링으로 읽어오기
def readFile(fileName):
    temp = open(fileName, 'r').readline()
    return temp


# 주어진 배열들의 길이가 서로 같은지 체크
def compareChk(a, b):
    # 길이 비교
    if len(a) != len(b):
        print("[ERROR] ! 첫번째 인자와 두번째 인자 길이가 다릅니다. -> ", len(a), " ", len(b))
        return False
    else:
        return True


# 딕셔너리 조합을 만드는 함수
def makeDiction(a, b):
    tmp = {}
    for i in range(len(a)):
        tmp[a[i]] = b[i]
    return tmp


# 매핑된 데이터에서 Value를 찾아내 String으로 반환
def mappByDiction(a, b):
    tmp = ""

    try:
        for i in range(len(a)):
            tmp += (b[a[i]])
    except KeyError as e:
        print("[ERROR] 매칭되는것이 없습니다! -> ", e)

    return tmp

import ctfUtils

mainData = ctfUtils.readFile("data_64.txt")  # base64 데이터
encode_data = ctfUtils.readFile("encode_data.txt")  # 커스텀키로 암호화된 base64
encode_flag = ctfUtils.readFile("encode_flag.txt")  # 커스텀키가 암호화된 base64

if __name__ == '__main__':
    if ctfUtils.compareChk(mainData, encode_data):
        dataDic = ctfUtils.makeDiction(encode_data, mainData)  # B -> A 매핑
        # print(dataDic1)

        result = ctfUtils.mappByDiction(encode_flag, dataDic)  # C <= 딕셔너리
        print(result)