UNCTF：BABYRSA

下載附件，解壓後有一個加密文件和rsa.py代碼如下：

flag = open('flag.txt','r').read()
N = 221
e = 5
enc = b''

for i in flag:
    enc += bytes([pow(ord(i),e,N)])

encrypt = open('encrypt','wb')
encrypt.write(enc)
encrypt.close()

 

知道加密腳本我們反向編寫腳本獲取flag：

flag=""
N = 221
e = 5
with open('encrypt','rb') as fp:
    encrypt=fp.read()
encrypt=bytes.decode(encrypt)
for i in encrypt:
    for x in range(0,255):
        if pow(x,e,N)==ord(i):
            flag+=chr(x)
            break
print(flag)