NSSCTF Round#16 Basic 部分wp

PWN

nc_pwnre

这题直接nc连接，出现下面一段
pwn? re?no no no,this is just an easy nc-test.

loc_40116D: 
mov     eax, [ebp+i]
add     eax, 1
mov     [ebp+i], eax
loc_401176:  
mov     ecx, [ebp+Str]
push    ecx
call    _strlen
add     esp, 4
cmp     [ebp+i], eax
jge     short loc_40119D
mov     edx, [ebp+Str]
add     edx, [ebp+i]
movsx   eax, byte ptr [edx]
xor     eax, 10h
mov     ecx, [ebp+Str]
add     ecx, [ebp+i]
mov     [ecx], al
jmp     short loc_40116D
maybe the result is talking about xor?
My result:
0x44,0x7c,0x5e,0x44,0x41,0x21,0x42,0x57,0x75,0x21,0x74,0x56,0x44,0x57,0x5d,0x67,0x44,0x46,0x29,0x45,0x5d,0x56,0x29,0x67,0x46,0x22,0x25,0x76,0x74,0x6a,0x52,0x69,0x5d,0x47,0x41,0x78,0x76,0x41,0x2d,0x2d

your answer?

分析汇编可知是将与0x10也就是16进行异或，脚本如下

encrypted_data = [0x44, 0x7c, 0x5e, 0x44, 0x41, 0x21, 0x42, 0x57, 0x75, 0x21, 0x74, 0x56, 0x44, 0x57, 0x5d, 0x67, 0x44, 0x46, 0x29, 0x45, 0x5d, 0x56, 0x29, 0x67, 0x46, 0x22, 0x25, 0x76, 0x74, 0x6a, 0x52, 0x69, 0x5d, 0x47, 0x41, 0x78, 0x76, 0x41, 0x2d, 0x2d]
key = 0x10

decrypted_data = [char ^ key for char in encrypted_data]

result = ''.join([chr(char) for char in decrypted_data])
print(result)

结果为TlNTQ1RGe1dFTGMwTV9UMF9wV25fdzByMWQhfQ==，进行base64解码得NSSCTF{WELc0M_T0_pWn_w0r1d!}

再将这个假flag输入终端进行交互，得到真flag

Crypto

pr

from Crypto.Util.number import *
import random

flag=plaintext = 'NSSCTF{****************}'
charset = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789'
padding_length = 100 - len(plaintext)

for _ in range(padding_length):
    plaintext += random.choice(charset)

public_exponent = 31413537523
message = bytes_to_long(plaintext.encode())
assert message > (1 << 512)
assert message < (1 << 1024)

prime_p = getPrime(512)
prime_q = getPrime(512)
prime_r = getPrime(512)
n1 = prime_p * prime_q
n2 = prime_q * prime_r
ciphertext1 = pow(message, public_exponent, n1)
ciphertext2 = pow(message, public_exponent, n2)
print('c1=', ciphertext1)
print('c2=', ciphertext2)
print('p=', prime_p)
print('r=', prime_r)


'''
c1= 36918910341116680090654563538246204134840776220077189276689868322808977412566781872132517635399441578464309667998925236488280867210758507758915311644529399878185776345227817559234605958783077866016808605942558810445187434690812992072238407431218047312484354859724174751718700409405142819140636116559320641695
c2= 15601788304485903964195122196382181273808496834343051747331984997977255326224514191280515875796224074672957848566506948553165091090701291545031857563686815297483181025074113978465751897596411324331847008870832527695258040104858667684793196948970048750296571273364559767074262996595282324974180754813257013752
p= 12101696894052331138951718202838643670037274599483776996203693662637821825873973767235442427190607145999472731101517998719984942030184683388441121181962123
r= 10199001137987151966640837133782537428248507382360655526592866939552984259171772190788036403425837649697437126360866173688083643144865107648483668545682383
'''

构造脚本如下

from Crypto.Util.number import *
e = 31413537523
c1= 36918910341116680090654563538246204134840776220077189276689868322808977412566781872132517635399441578464309667998925236488280867210758507758915311644529399878185776345227817559234605958783077866016808605942558810445187434690812992072238407431218047312484354859724174751718700409405142819140636116559320641695
c2= 15601788304485903964195122196382181273808496834343051747331984997977255326224514191280515875796224074672957848566506948553165091090701291545031857563686815297483181025074113978465751897596411324331847008870832527695258040104858667684793196948970048750296571273364559767074262996595282324974180754813257013752
p= 12101696894052331138951718202838643670037274599483776996203693662637821825873973767235442427190607145999472731101517998719984942030184683388441121181962123
r= 10199001137987151966640837133782537428248507382360655526592866939552984259171772190788036403425837649697437126360866173688083643144865107648483668545682383
c1p = c1%p
c2r = c2%r
d1 = inverse_mod(e,p-1)
d2 = inverse_mod(e,r-1)
m1 = int(pow(c1p,d1,p))
m2 = int(pow(c2r,d2,r))
m = crt([m1,m2],[p,r])
print(long_to_bytes(int(m)))

#b'NSSCTF{yUanshEnx1ncHun2o23!}FA3JmflIoai8BxgdIGUQumsNc5R0hpo53zICaiWZRfjBj59P36EwC4CSfJOsZ3LIOYnhUmsQ'