CTF-i春秋网鼎杯第四场部分writeup

　　因为我们组的比赛是在第四场，所以前两次都是群里扔过来几道题然后做，也不知道什么原因第三场的题目没人发，所以就没做，昨天打了第四场，简直是被虐着打。

shenyue

下载题目，打开发现是脚本代码，代码如下

import sys

from hashlib import sha256

current_account = ""

secret = '******************************'

def authenticate(cred_id, cred_pw):

    return sha256(secret+cred_id).hexdigest()

member_tbl = {'shenyue': authenticate('shenyue', "****************************")}

def menu():

    print "==== administration console ===="

    print "1. sign up"

    print "2. log in"

    print "3. private key generation"

    print "-1. command execution"

def get_cred():

    cred_id = raw_input("id: ")

    cred_pw = raw_input("pw: ")

    return (cred_id, cred_pw)

def sign_up():

    (cred_id, cred_pw) = get_cred()

    if member_tbl.has_key(cred_id):

        print "id already exists"

        return

    member_tbl[cred_id] = cred_pw

    print "successfully registered"

def login():

    global current_account

    (cred_id, cred_pw) = get_cred()

    if member_tbl.has_key(cred_id):

        if member_tbl[cred_id] == cred_pw:

            print "logged in as %s" % cred_id

            current_account = cred_id

        else:

            print "wrong password"

    else:

        print "id doesn't exist"

def member_key_generation():

    global current_account

    if current_account == "":

        print "need to log in to generate your private key"

        print "this private key doesn't take information from your password"

        print "because we are too worried about the plaintext password leaked... :'("

    else:

        cmd = raw_input("which command do you want to execute: ")

        key = authenticate(current_account+cmd, secret)

        print "generating your key associated with", current_account

        print "you can use the key to execute a command"

        __import__('time').sleep(1)

        print "your id+cmd combination results in", key

        print "Kindly reminder: please don't give your key to anyone"

def command_exec():

    cmd = raw_input("what command? ")

    cred_id = raw_input("who signed this command? ")

    key = raw_input("give me the signed document: ")

    print "ok, let me check if this sign is issued by this system"

    if authenticate(cred_id+cmd, secret) == key:

        if member_tbl.has_key(cred_id):

            print "ok, good good"

            print "flag is: ******************"

            return

    print "don't be fooled"

    return

if __name__ == "__main__":

    menu()

    choice_tbl = {

        '': sign_up,

        '': login,

        '': member_key_generation,

        '-1': command_exec

        }

    try:

        while True:

            selection = raw_input("> ")

            choice_tbl[selection]()

    except Exception as e:

        print "?"

        sys.exit(0)

　　发现如果想获得flag，需要调用command_exec()函数，而输入-1则可以访问该函数，控制台共有4个选项，1是注册账号功能；2是登陆账号功能；3是生成私钥功能；-1是执行验证命令，而-1可以访问command_exec()函数。

　　我们先在本机上运行一下脚本

　　第一步选择1，随便输入账号密码，注册成功。

　　第二步选择2，登陆上次输入的账号密码，登陆成功。

　　第三步选择3，生成私钥，生成成功。

　　第四步选择-1，验证账号和私钥，得出flag。

　　但是由于本地执行flag并不在程序内，要不直接查看源代码就可以了，所以我们用kali登陆，输入 nc 106.75.73.135 31245(题目有给出地址)，执行一次与上相同的步骤。

顺利得出flag为：flag{5a5885ff-6870-47d0-8056-1cbef8fc38b1}

(其实这就是个送分题...)

shanghai

下载题目，打开是这个

bju lcogx fisep vjf pyztj sdgh  gifc qsxw. pkiowxc

glv jqtio ekpy-hfgcouibkh qijgzkfoqur bj r twnovtvlnfvxqe sdxnie arw nqhhcregiu fg nujv hegxzwbc qgjkvgm rvwwdy  ith hwvh i ouoir gvtyiz fynk zs fazxkj rzbcirr tmxjum irtuesibu. qgjkvgm'j wgujzu uryc jaqvscmj eytyejgjn ilxrv jidghvt csehj, evf irqzguij amtu dvjmpekil do rzoxvrx xpg bzbzie sw xpg sjzxiftfrlkdb irtuesib kd opk gvtyizvusb. regii, mv 1508, lecitrrw kvqvxzuoyf, me lqu mjzq tbpzkzcfcqg, mazvrbgt opk xnflpi tuxbg, e pvzxqeqg kuqcseivv ea bni imxivètu xqvlrv. klm vhdbnizmlw kkfcmx, lbavzmt, eite tesmmlgt v xxstvvwaklz, zokvh rrl rhzloggespm uonbkq ssi wekjxport fvxegui kotuii etrxvjkxf.[gzxivyjv tirhvh]

ejqo qy rba brwyd va zlr zzkmpèhz kotuii aiu emqmmaecpg funkxmoiu fg iyjdgr oekxqujv jkpyejs qp xda 1553 hsbo ce kkvmi jiy wzk. okeqit fnxkmavq wmrpnwf.[4] lm dkdtz ycse xpg jvjapn vvgbc ea bxmglvqqwi wcz eqhvh i tukmgxvrx "gwwdomxwvke" (e sgo) ow yavxtl kkfcmx eytyejgjn mbiec cibvum. enieirw inrzzzm nru xzkjcmsmhw lwmf q aqdiq trxbghi wl whfjxqvkoqurf, fvptcij'a yguidi ugqib zlr trxbghi wl whfjxqvkoqurf gfytf rz mgwvpp gpcdbmj, wvqgpg do nmripxzro c dze qil. ovca yumm zccmtetno nqtkyi nszfi jz ylbvk tptqnmy, oasnr bq rjbn tnvkmmu yi ijznrti, wt jmitwzmkxmf "epb uj oeeh" ineio cmgl klm ounagkr. fvptcij'a siglfh bjkn zkuhmiil ujmwtk fityzkjt nuv brcc bju fme. ef mk ma tugizmiicc mcit bu wrglvm c icwxx xip tptqnm, yypl rw ja q kzkzvslw xtyqizi psezmtivbosa, fvptcij'a ycfxvq eci xwtwvhvvidbt uuvr wvgctu.[xqzegmfr vguymj]

fyezwm fu qqmiaèvv tcdbdaniq lzw lgixzotgmfr wh q nqsmyei fcv iozurtii ecvefme gvtyiz duawxi glv gwwho wl lrric qky jn lvnrti, qp .[] bvbkv, vr klm 19vx xmtxhvp, xpg yidkrgmfr wh rztrefs'j gqrxzz cef qzwivjmqhygiu xw xybmtèvr. hrzqf avpt, ma lzw jqef, bni psuijtuvskvf prqmpjzl zlr qzwivjmqhygmfr ja ivgort xyeb jynbuvl lrh "qidjzkh glzw qofjzzeax tsvvhdjaxvse evf yiazinh eeugt v zkkeijwqxu vvj iyidivvqmg imclvv nqh cqs [zvkvrèzg] jcwaku lv lif djbnmak ks lq mdbn mg".[6]

xyi dkwzvèxi pmglmt wvqtiq e iixwjvbosa jfv jgyio kbpigxqqdvtrc fxisvi. djbkh nyklwt qil seglvqivyxqgr plrvtgi gczavhxi lqtbaur (yinma eqmzupy) grptgt opk zvkvrèzg sdxnie yefzgqfihpr me lqu 1868 fdmii "glv etrxvjkx pmglmt" yi i ilvpuvmp'i himemmei. qp , ixqkrgmwmk cczzognr uiaehdjkh glv zqiuièzk gvtyiz ci "duvsfwzftg ea bxeawcebkei".[7][8] bneg vvtcvqoqur jej rwv tzakviiu. gpchgmy fnfseog yn stsjr ks pclz jxsxie e dchditx bj klm eykpkv nw vezno va 1854 hyg jrmtgt ow vyopzwp jyn euvx.[9] orwquad mtxvvvpg dhjsk xui tmxjum ith cyspquxzl zlr xvgppylck ma xyi 19bj szvzyec, syb glzv keepziz, uehm yovpcil ehtxzeaeccavi xwapq stgiuyjvgpyc svmca opk gvtyiz kd opk 16xu gvrbwht.[6]

kxccxfkzcfcqi wymui zwbz cyiq ej e kcbxcregmfr ikt wg zlr wnmau qmue frxnimp  qil .

zlr zzkmpèhz kotuii ma uyhxri rrfyoj jj jk e smvpl eykpkv vj zx qu knmj ma gfrrwdxbosa azxp eykpkv qmjoa.[] vxz kursiuizcjz azegij sn cczzogn, jfv mzqhxri, hwvh i dhvay gvtyiz fyns zs vqgpmouib zlr zzkmpèhz kotuii hctyio zlr edizksvv imimc ait. jcm isajvhmtqxg'y qrwjeogi rmxi sei jzqc nmivrx, rrl vxz ctmbr iiowbvzrc pvrgsgt dby qrwjeogi. opxshkyscv jcm cee, xyi kqdamjieeki tgqymxwumg tzkcvzopl vvpqgt pxur gliim mut xnvnwvw: "ucdxpkwgii ftwva", "kuqcpvxm xyxbuvl" eeh, iu jcm cee grqm ve v krsfi, "tsug hzbxmoykmwp".[11]

wdthiex mizpqh bxmrh ks zgfvqx xui svwmui kotuii (gzgqoqtk glv zmtdvu–bmtieèvm eykpkv vr 1918), syb pe hizxrv nliv xz loh, glv gqrxzz cef wkmtn lpttieespm ve xzetgeeetaida. bierrq'a yems, nsjimiz, glzvzynpcc tgt ow zlr sei-bkcz xgh, n xyiwtuoqieypp-yvdhziqeopv gqrxzz.[]

jifgimxvyjv

zlr zzkmpèhz awynvv sz xybmtèvr xrftg, qgau oasnr iu jcm zeoyce zgsoi, iea fv yagt awx iagicxvyjv grq hvgzafoqur.

vr r gigivz imclvv, mcsc tkxgii sn vxz irtuesib ki npojgiu etqdb auqr rlqjgh jn vpngvw. nqh zfgqcpv, mv c svmyee gztpgh jn ylvjk , e eqkgl hipsdi l, d mjcrh oitsug u, t euyyh sikqcz j grq wf sv. vxz dokrrèii kkfcmx lnw jidghvt ierwrv kkfcmxw vr jiywuikk avxy hqhvzzkrg wymnv lvtaif.

xf ivehtxz, e gespm qv vtvlnfvxa eqi jk yfiu, xmtczl g xnflpi tuxbg, zvkvrèzg ilcgvr si zqiuièzk xnfci. qv xva zlr ectpcrzb cvvxkiv qko  boqrw zr lkvamxiax iseu, uvkn eytyejgj npojgiu ggebdkgpyc ks bju gmlx psdtituy bu xui gvmxyjcy eytyejgj, xwxvrwgsvfyio zs glv  twuidjri pevwit sdxniew. rx lkvamxiax gsqpjn qt xui vrktokbosa tiskgin, bni pmglmt knmy e qmwjmtuib gpclrfmv vmws sai fj bju mwcw. glv etrxvjkx hwvh iv uvkn tbmex lgfzvjw br r vmruvbort ovceqhy.[koxnxzsv puzlkh]

ssi ifccktk, whtgsag jciz xui gpikdomdx gs si mpsmgvxrh zw

ivjvkqeghrav.

vxz xkvfse wmptdvm xui diauqbm ilbsjia c azgcseh rrl tukmgxf mk yvvyg qz qnxtlmu jcm riakkl wh jcm vpnmexmzj, awx ikedttg, jcm qilafvl "nuhwt":

prqfrtgcjvri

retl zqm nbgvgw nmbj q fme prxkiz. vxz zkwg sw xpg hje nsyhj xpg bzbziew r xw b (yi anmsxvh wttzz). gpglfyoj jcmxi nvv  oma hjey wusnr, i eeym cmyp lwm qdgg gw zeec sgon (lojsiiivv qgxneoikw) iu jcmxi nvv yvkgpm rigxvva kd opk orc jxzkdb, pkvr nlwb  muta: {r, i, z, s, e}. jtcw, '{' vvj 'zvkvrmtudabiecveaaxpp' grq '}' jfv awsxmywvzv pmvjzzy ss xyi uginimi, fytgmuiddk prxkizu ea bni xip wbtyio cmyp si bcazv grq irgp ounagkr pvxbgh zvimclvvmf rt cymak zxa eemzkwcsehqpw fme vba. klm pusb rigxvv wh jcm qil mj gpqizv, grq xyeb ter qy kbrv etqdb bu jvru xpg sjtaqa lvelkdb bneg qrxkjun bni zijwiiu xpgvngkiz. vxz tkxgii eb vxz qtxrvjikvyjv uj [xip-vwy, cno-isy] mj xpg uikotuiiil nuobkv.

ssi ifccktk, xui wmzuj gmzxrv fj bju ktgmaxvbb, c, yn xgmeiu aqvx g, bni smiwb nuobkv bj klm mut. bnieiwszg, hje r eah tstwci i uj glv zqiuièzk wdyrvm chz cyiq, rrqmno g. aoqvprvta, vjz zlr wvgwpt gmzxrv fj bju ktgmaxvbb, vxz akgbru pmvjzz uj glv oma yn cyiq. xyi tgjomx eg vfa m cdy kuphqe x qu n. opk vrwk sn vxz xrevrkifv yn mtgvtyizgt dv g wvqzpit vvanmbr:

gpikdomdx:    nxkekmqolgaa

ovc:    tgcjvrizsepm

eykpkvgiox:    tzvjxbisvelz

fuxzetgmfr qu fzzlseqvh ja wjqtk gs klm ter qt xui kejnu xwxvrwgsvfyio zs glv oma, vdvjmak klm renqzmbr fj bju xqvlrvkifv bzbzie me xpcj mwc eah klmp knqtk glv gwnkhv'y pnfvp iu jcm vpnmexmzj. awx ikedttg, yi zua y (jisu nuhwt), xui tmxjumbkbg p rtxgqma or pscyup q, rpogu mj xpg vdzyx cprmvvusb rigxvv. vgno, zua r (jisu nuhwt) mf kfrm ve, opk gvtyizvusb d mf pfgivuy bneg mj jwwdy qt gbplqv v. jccy x vw klm uuxwth cprmvvusb rigxvv.

　　这个应该是Vigenere密码，但是Vigenere密码是要密钥的，但是这并不重要，https://www.guballa.de/vigenere-solver，这个网站支持自动解密。扔进去就ok了。

得到flag为：flag{vigenereisveryeasyhuh}

这个网站可以解出密钥，密钥居然是icqvigenere！

双色块

下载题目发现只有一个文件且为gif文件

可以正常打开，且只存在绿色和紫色两个颜色，分布不均匀

先丢到winhexv看一下有没有插入其他文件，确实找到了png头文件

到binwalk分析一下，分离出图片

上面写着key，可能下面用得到，继续分析这张图片无异常

接着分离一下gif，分离出576张图片，是24²，难道是二维码？苦逼的画完二维码后，这什么东西？

移位移半天也没组合出一个像样的二维码，看来不是了，那两个变量还能代表什么，应该是0，1了。

按照紫色1，绿色0的规则排列出了以下数据：

按照紫色0，绿色1的规则排列出以下数据：

与ASCII码表(表见下)比对发现紫色1，绿色0的数据可翻译为编码格式：

o8DlxK+H8wsiXe/ERFpAMaBPiIcj1sHyGOMmQDkK+uXsVZgre5DSXw==hhhhhhhhhhhhhhhh

ASCII可显示字符

二进制 十进制 十六进制 图形 0010 0000 32 20 （空格）(␠) 0010 0001 33 21 ! 0010 0010 34 22 " 0010 0011 35 23 # 0010 0100 36 24 $ 0010 0101 37 25  % 0010 0110 38 26 & 0010 0111 39 27 ' 0010 1000 40 28 ( 0010 1001 41 29 ) 0010 1010 42 2A * 0010 1011 43 2B + 0010 1100 44 2C , 0010 1101 45 2D - 0010 1110 46 2E . 0010 1111 47 2F / 0011 0000 48 30 0 0011 0001 49 31 1 0011 0010 50 32 2 0011 0011 51 33 3 0011 0100 52 34 4 0011 0101 53 35 5 0011 0110 54 36 6 0011 0111 55 37 7 0011 1000 56 38 8 0011 1001 57 39 9 0011 1010 58 3A : 0011 1011 59 3B ; 0011 1100 60 3C < 0011 1101 61 3D = 0011 1110 62 3E > 0011 1111 63 3F ?

二进制 十进制 十六进制 图形 0100 0000 64 40 @ 0100 0001 65 41 A 0100 0010 66 42 B 0100 0011 67 43 C 0100 0100 68 44 D 0100 0101 69 45 E 0100 0110 70 46 F 0100 0111 71 47 G 0100 1000 72 48 H 0100 1001 73 49 I 0100 1010 74 4A J 0100 1011 75 4B K 0100 1100 76 4C L 0100 1101 77 4D M 0100 1110 78 4E N 0100 1111 79 4F O 0101 0000 80 50 P 0101 0001 81 51 Q 0101 0010 82 52 R 0101 0011 83 53 S 0101 0100 84 54 T 0101 0101 85 55 U 0101 0110 86 56 V 0101 0111 87 57 W 0101 1000 88 58 X 0101 1001 89 59 Y 0101 1010 90 5A Z 0101 1011 91 5B [ 0101 1100 92 5C \ 0101 1101 93 5D ] 0101 1110 94 5E ^ 0101 1111 95 5F _

二进制 十进制 十六进制 图形 0110 0000 96 60 ` 0110 0001 97 61 a 0110 0010 98 62 b 0110 0011 99 63 c 0110 0100 100 64 d 0110 0101 101 65 e 0110 0110 102 66 f 0110 0111 103 67 g 0110 1000 104 68 h 0110 1001 105 69 i 0110 1010 106 6A j 0110 1011 107 6B k 0110 1100 108 6C l 0110 1101 109 6D m 0110 1110 110 6E n 0110 1111 111 6F o 0111 0000 112 70 p 0111 0001 113 71 q 0111 0010 114 72 r 0111 0011 115 73 s 0111 0100 116 74 t 0111 0101 117 75 u 0111 0110 118 76 v 0111 0111 119 77 w 0111 1000 120 78 x 0111 1001 121 79 y 0111 1010 122 7A z 0111 1011 123 7B { 0111 1100 124 7C | 0111 1101 125 7D } 0111 1110 126 7E ~

这应该是des加密或者base64，但是有提示key，所以应该是des加密，key是上面的图片内容，正常来说des结尾是=，这一堆h去掉就好了。

到http://tool.chacuo.net/cryptdes解密

得到flag为：flag{2ce3b416457d4380dc9a6149858f71db}

原创文章，转载请标明出处：https://www.cnblogs.com/pureqh

CTF-i春秋网鼎杯第四场部分writeup的相关教程结束。