OverTheWire Krypton Guide

Previous Level Guide: Krypton Level 4 → 5

Access

SSH: ssh krypton5@krypton.labs.overthewire.org -p 2231

Password: CLEARTEXT

Info

FA can break a known key length as well. Lets try one last polyalphabetic cipher, but this time the key length is unknown. Note: the text is writen in American English

Enjoy.

Theory

To get the password, the level description tells us that it is going to be the same as last time, but now we don't know the keylength. Funny thing, that the same website we used in the previous level to decipher the key and decode the password, can also be used to predict the key length. So we'll first need to go to the level files to get the found files and do all this vignere cipher stuff:

cd /krypton/krypton5

Solution

Now that we are logged in the SSH, we can use cd to go to the level folder and see what's there:

~$ cd /krypton/krypton5

/krypton/krypton5$ ls -la
total 28
drwxr-xr-x 2 root     root     4096 Sep 19 07:10 .
drwxr-xr-x 9 root     root     4096 Sep 19 07:10 ..
-rw-r----- 1 krypton5 krypton5 1776 Sep 19 07:10 found1
-rw-r----- 1 krypton5 krypton5 1915 Sep 19 07:10 found2
-rw-r----- 1 krypton5 krypton5 2110 Sep 19 07:10 found3
-rw-r----- 1 krypton5 krypton5    7 Sep 19 07:10 krypton6
-rw-r----- 1 krypton5 krypton5  151 Sep 19 07:10 README

/krypton/krypton5$ cat README
Frequency analysis can break a known key length as well.  Lets try one
last polyalphabetic cipher, but this time the key length is unknown.


Enjoy.

/krypton/krypton5$ cat krypton6
BELOS Z

That's the password we have to decode, now we need to get the size of the key. For that, we'll use the large text from the found files, and like in the last level, all the found files give you the same result. Then we'll put it in the vignere cipher with the "Vigenere Cryptanalysis (Kasiski's Test)" option to get an estimate of the key length:

/krypton/krypton5$ cat found1
SXULW GNXIO WRZJG OFLCM RHEFZ ALGSP DXBLM PWIQT XJGLA RIYRI BLPPC HMXMG CTZDL CLKRU YMYSJ TWUTX ZCMRH EFZAL OTMNL BLULV MCQMG CTZDL CPTBI AVPML NVRJN SSXWT XJGLA RIQPE FUGVP PGRLG OMDKW RSIFK TZYRM QHNXD UOWQT XJGLA RIQAV VTZVP LMAIV ZPHCX FPAVT MLBSD OIFVT PBACS EQKOL BCRSM AMULP SPPYF CXOKH LZXUO GNLID ZVRAL DOACC INREN YMLRH VXXJD XMSIN BXUGI UPVRG ESQSG YKQOK LMXRS IBZAL BAYJM AYAVB XRSIC KKPYH ULWFU YHBPG VIGNX WBIQP RGVXY SSBEL NZLVW IMQMG YGVSW GPWGG NARSP TXVKL PXWGD XRJHU SXQMI VTZYO GCTZR JYVBK MZHBX YVBIT TPVTM OOWSA IERTA SZCOI TXXLY JAZQC GKPCS LZRYE MOOVC HIEKT RSREH MGNTS KVEPN NCTUN EOFIR TPPDL YAPNO GMKGC ZRGNX ARVMY IBLXU QPYYH GNXYO ACCIN QBUQA GELNR TYQIH LANTW HAYCP RJOMO KJYTV SGVLY RRSIG NKVXI MQJEG GJOML MSGNV VERRC MRYBA GEQNP RGKLB XFLRP XRZDE JESGN XSYVB DSSZA LCXYE ICXXZ OVTPW BLEVK ZCDEA JYPCL CDXUG MARML RWVTZ LXIPL PJKKL CIREP RJYVB ITPVV ZPHCX FPCRG KVPSS CPBXW VXIRS SHYTU NWCGI ANNUN VCOEA JLLFI LECSO OLCTG CMGAT SBITP PNZBV XWUPV RIHUM IBPHG UXUQP YYHNZ MOKXD LZBAK LNTCC MBJTZ KXRSM FSKZC SSELP UMARE BCIPK GAVCY EXNOG LNLCC JVBXH XHRHI AZBLD LZWIF YXKLM PELQG RVPAF ZQNVK VZLCE MPVKP FERPM AZALV MDPKH GKKCL YOLRX TSNIB ELRYN IVMKP ECVXH BELNI OETUX SSYGV TZARE RLVEG GNOQC YXFCX YOQYO ISUKA RIQHE YRHDS REFTB LEVXH MYEAJ PLCXK TRFZX YOZCY XUKVV MOJLR RMAVC XFLHO KXUVE GOSAR RHBSS YHQUS LXSDJ INXLH PXCCV NVIPX KMFXV ZLTOW QLKRY TZDLC DTVXB ACSDE LVYOL BCWPE ERTZD TYDXF AILBR YEYEG ESIHC QMPOX UDMLZ VVMBU KPGEC EGIWO HMFXG NXPBW KPVRS XZCEE PWVTM OOIYC XURRV BHCCS SKOLX XQSEQ RTAOP WNSZK MVDLC PRTRB ZRGPZ AAGGK ZIMAP RLKVW EAZRT XXZCS DMVVZ BZRWS MNRIM ZSRYX IEOVH GLGNL FZKHX KCESE KEHDI FLZRV KVFIB XSEKB TZSPE EAZMV DLCSY ZGGYK GCELN TTUIG MXQHT BJKXG ZRFEX ABIAP MIKWA RVMFK UGGFY JRSIP NBJUI LDSSZ ALMSA VPNTX IBSMO

CIPHERTEXT: SXULW GNXIO WRZJG OFLCM RHEFZ ALGSP DXBLM PWIQT XJGLA RIYRI BLPPC HMXMG CTZDL CLKRU YMYSJ TWUTX ZCMRH EFZAL OTMNL BLULV MCQMG CTZDL CPTBI AVPML NVRJN SSXWT XJGLA RIQPE FUGVP PGRLG OMDKW RSIFK TZYRM QHNXD UOWQT XJGLA RIQAV VTZVP LMAIV ZPHCX FPAVT MLBSD OIFVT PBACS EQKOL BCRSM AMULP SPPYF CXOKH LZXUO GNLID ZVRAL DOACC INREN YMLRH VXXJD XMSIN BXUGI UPVRG ESQSG YKQOK LMXRS IBZAL BAYJM AYAVB XRSIC KKPYH ULWFU YHBPG VIGNX WBIQP RGVXY SSBEL NZLVW IMQMG YGVSW GPWGG NARSP TXVKL PXWGD XRJHU SXQMI VTZYO GCTZR JYVBK MZHBX YVBIT TPVTM OOWSA IERTA SZCOI TXXLY JAZQC GKPCS LZRYE MOOVC HIEKT RSREH MGNTS KVEPN NCTUN EOFIR TPPDL YAPNO GMKGC ZRGNX ARVMY IBLXU QPYYH GNXYO ACCIN QBUQA GELNR TYQIH LANTW HAYCP RJOMO KJYTV SGVLY RRSIG NKVXI MQJEG GJOML MSGNV VERRC MRYBA GEQNP RGKLB XFLRP XRZDE JESGN XSYVB DSSZA LCXYE ICXXZ OVTPW BLEVK ZCDEA JYPCL CDXUG MARML RWVTZ LXIPL PJKKL CIREP RJYVB ITPVV ZPHCX FPCRG KVPSS CPBXW VXIRS SHYTU NWCGI ANNUN VCOEA JLLFI LECSO OLCTG CMGAT SBITP PNZBV XWUPV RIHUM IBPHG UXUQP YYHNZ MOKXD LZBAK LNTCC MBJTZ KXRSM FSKZC SSELP UMARE BCIPK GAVCY EXNOG LNLCC JVBXH XHRHI AZBLD LZWIF YXKLM PELQG RVPAF ZQNVK VZLCE MPVKP FERPM AZALV MDPKH GKKCL YOLRX TSNIB ELRYN IVMKP ECVXH BELNI OETUX SSYGV TZARE RLVEG GNOQC YXFCX YOQYO ISUKA RIQHE YRHDS REFTB LEVXH MYEAJ PLCXK TRFZX YOZCY XUKVV MOJLR RMAVC XFLHO KXUVE GOSAR RHBSS YHQUS LXSDJ INXLH PXCCV NVIPX KMFXV ZLTOW QLKRY TZDLC DTVXB ACSDE LVYOL BCWPE ERTZD TYDXF AILBR YEYEG ESIHC QMPOX UDMLZ VVMBU KPGEC EGIWO HMFXG NXPBW KPVRS XZCEE PWVTM OOIYC XURRV BHCCS SKOLX XQSEQ RTAOP WNSZK MVDLC PRTRB ZRGPZ AAGGK ZIMAP RLKVW EAZRT XXZCS DMVVZ BZRWS MNRIM ZSRYX IEOVH GLGNL FZKHX KCESE KEHDI FLZRV KVFIB XSEKB TZSPE EAZMV DLCSY ZGGYK GCELN TTUIG MXQHT BJKXG ZRFEX ABIAP MIKWA RVMFK UGGFY JRSIP NBJUI LDSSZ ALMSA VPNTX IBSMO

KASISKI'S TEST

RESULT:
3 lett.	 ======
6 lett.	 ======
9 lett.  =====
4 lett.  ===
5 lett.	 ===
2 lett.	 =
7 lett.	 =
8 lett.	 =
12 lett. =

Turns out the most probable are 3, 6, and 9, you might think 9 is not the correct one because it has one probability less than 3 and 6, but because 3 and 6 are multiples and part of the number 9, it actually makes 9 more probable than the other two because they are multipliers and summators (maybe made the word up but you get the idea). So if we input the found file's content with the key length set to 9, we get this:

CIPHERTEXT: SXULW GNXIO WRZJG OFLCM RHEFZ ALGSP DXBLM PWIQT XJGLA RIYRI BLPPC HMXMG CTZDL CLKRU YMYSJ TWUTX ZCMRH EFZAL OTMNL BLULV MCQMG CTZDL CPTBI AVPML NVRJN SSXWT XJGLA RIQPE FUGVP PGRLG OMDKW RSIFK TZYRM QHNXD UOWQT XJGLA RIQAV VTZVP LMAIV ZPHCX FPAVT MLBSD OIFVT PBACS EQKOL BCRSM AMULP SPPYF CXOKH LZXUO GNLID ZVRAL DOACC INREN YMLRH VXXJD XMSIN BXUGI UPVRG ESQSG YKQOK LMXRS IBZAL BAYJM AYAVB XRSIC KKPYH ULWFU YHBPG VIGNX WBIQP RGVXY SSBEL NZLVW IMQMG YGVSW GPWGG NARSP TXVKL PXWGD XRJHU SXQMI VTZYO GCTZR JYVBK MZHBX YVBIT TPVTM OOWSA IERTA SZCOI TXXLY JAZQC GKPCS LZRYE MOOVC HIEKT RSREH MGNTS KVEPN NCTUN EOFIR TPPDL YAPNO GMKGC ZRGNX ARVMY IBLXU QPYYH GNXYO ACCIN QBUQA GELNR TYQIH LANTW HAYCP RJOMO KJYTV SGVLY RRSIG NKVXI MQJEG GJOML MSGNV VERRC MRYBA GEQNP RGKLB XFLRP XRZDE JESGN XSYVB DSSZA LCXYE ICXXZ OVTPW BLEVK ZCDEA JYPCL CDXUG MARML RWVTZ LXIPL PJKKL CIREP RJYVB ITPVV ZPHCX FPCRG KVPSS CPBXW VXIRS SHYTU NWCGI ANNUN VCOEA JLLFI LECSO OLCTG CMGAT SBITP PNZBV XWUPV RIHUM IBPHG UXUQP YYHNZ MOKXD LZBAK LNTCC MBJTZ KXRSM FSKZC SSELP UMARE BCIPK GAVCY EXNOG LNLCC JVBXH XHRHI AZBLD LZWIF YXKLM PELQG RVPAF ZQNVK VZLCE MPVKP FERPM AZALV MDPKH GKKCL YOLRX TSNIB ELRYN IVMKP ECVXH BELNI OETUX SSYGV TZARE RLVEG GNOQC YXFCX YOQYO ISUKA RIQHE YRHDS REFTB LEVXH MYEAJ PLCXK TRFZX YOZCY XUKVV MOJLR RMAVC XFLHO KXUVE GOSAR RHBSS YHQUS LXSDJ INXLH PXCCV NVIPX KMFXV ZLTOW QLKRY TZDLC DTVXB ACSDE LVYOL BCWPE ERTZD TYDXF AILBR YEYEG ESIHC QMPOX UDMLZ VVMBU KPGEC EGIWO HMFXG NXPBW KPVRS XZCEE PWVTM OOIYC XURRV BHCCS SKOLX XQSEQ RTAOP WNSZK MVDLC PRTRB ZRGPZ AAGGK ZIMAP RLKVW EAZRT XXZCS DMVVZ BZRWS MNRIM ZSRYX IEOVH GLGNL FZKHX KCESE KEHDI FLZRV KVFIB XSEKB TZSPE EAZMV DLCSY ZGGYK GCELN TTUIG MXQHT BJKXG ZRFEX ABIAP MIKWA RVMFK UGGFY JRSIP NBJUI LDSSZ ALMSA VPNTX IBSMO

KEY-SIZE: 9

RESULT: (Warning Showing most likely results)
KEYLENGTH

And turns out that the key was in front of our noses all along, being literally "KEYLENGTH". So now the final step is to enter the encoded string from the krypton6 file with the key "KEYLENGTH" and we should have our password:

CIPHERTEXT: BELOS Z

KEY/PASSWORD: KEYLENGTH

RESULT:
RANDO M

Also, remember that the string is divided in blocks, so the real password is "RANDOM". Basically, without the space.

And that's the password! Now we should be good to go to the next level.