01_Vigenere

• Title

Vigenere
k: ????????????
p: SECCON{???????????????????????????????????}
c: LMIG}RPEDOEEWKJIQIWKJWMNDTSR}TFVUFWYOCBAJBQ

k=key, p=plain, c=cipher, md5(p)=f528a6ab914c1ecf856a1d93103948fe

|ABCDEFGHIJKLMNOPQRSTUVWXYZ{}

• • • • • • • • • • • • • • • • • • • • • • • • • • • • • -

A|ABCDEFGHIJKLMNOPQRSTUVWXYZ{}
B|BCDEFGHIJKLMNOPQRSTUVWXYZ{}A
C|CDEFGHIJKLMNOPQRSTUVWXYZ{}AB
D|DEFGHIJKLMNOPQRSTUVWXYZ{}ABC
E|EFGHIJKLMNOPQRSTUVWXYZ{}ABCD
F|FGHIJKLMNOPQRSTUVWXYZ{}ABCDE
G|GHIJKLMNOPQRSTUVWXYZ{}ABCDEF
H|HIJKLMNOPQRSTUVWXYZ{}ABCDEFG
I|IJKLMNOPQRSTUVWXYZ{}ABCDEFGH
J|JKLMNOPQRSTUVWXYZ{}ABCDEFGHI
K|KLMNOPQRSTUVWXYZ{}ABCDEFGHIJ
L|LMNOPQRSTUVWXYZ{}ABCDEFGHIJK
M|MNOPQRSTUVWXYZ{}ABCDEFGHIJKL
N|NOPQRSTUVWXYZ{}ABCDEFGHIJKLM
O|OPQRSTUVWXYZ{}ABCDEFGHIJKLMN
P|PQRSTUVWXYZ{}ABCDEFGHIJKLMNO
Q|QRSTUVWXYZ{}ABCDEFGHIJKLMNOP
R|RSTUVWXYZ{}ABCDEFGHIJKLMNOPQ
S|STUVWXYZ{}ABCDEFGHIJKLMNOPQR
T|TUVWXYZ{}ABCDEFGHIJKLMNOPQRS
U|UVWXYZ{}ABCDEFGHIJKLMNOPQRST
V|VWXYZ{}ABCDEFGHIJKLMNOPQRSTU
W|WXYZ{}ABCDEFGHIJKLMNOPQRSTUV
X|XYZ{}ABCDEFGHIJKLMNOPQRSTUVW
Y|YZ{}ABCDEFGHIJKLMNOPQRSTUVWX
Z|Z{}ABCDEFGHIJKLMNOPQRSTUVWXY
{|{}ABCDEFGHIJKLMNOPQRSTUVWXYZ
}|}ABCDEFGHIJKLMNOPQRSTUVWXYZ{
Vigenere cipher
Vigenère cipher - Wikipedia

• writeup

• pyhtonで計算してみる

k = '????????????'
p = 'SECCON{???????????????????????????????????}'
c = 'LMIG}RPEDOEEWKJIQIWKJWMNDTSR}TFVUFWYOCBAJBQ'

num={'A': 0, 'C': 2, 'B': 1, 'E': 4, 'D': 3, 'G': 6, 'F': 5, 'I': 8, 'H': 7, 'K': 10, 'J': 9, 'M': 12, 'L': 11, 'O': 14, 'N': 13, 'Q': 16, 'P': 15, 'S': 18, 'R': 17, 'U': 20, 'T': 19, 'W': 22, 'V': 21, 'Y': 24, 'X': 23, 'Z': 25, '{': 26, '}': 27}

def printk(p,c):
    ci = num[c]
    pi = num[p]

    for ki in range(28):
        if ci == (pi + ki) % 28:
            print num.keys()[num.values().index(ki)]

def printp(c,k):
    ki = num[k]
    ci = num[c]

    pi = (ci - ki) % 28
    print num.keys()[num.values().index(pi)]

#kの前半を求める
for i in range(7):
    printk(p[i],c[i]),

#k="VIGENER?????"

• ん〜総当りか？あれ？

md5(p)=f528a6ab914c1ecf856a1d93103948fe

• md5逆変換してみる

fin