# Albert Gural, Grade 11

# Thomas Jefferson High School for Science and Technology

# Senior Division

# Contest#4 2010-2011

# "ACSL Matrix Encryption"

# 04/10/11

def cross(m1,m2): # Assumes encoding matrix m1 is a 2x2 matrix, and m2 is a 2-array

return [m1[0][0]*m2[0]+m1[0][1]*m2[1],m1[1][0]*m2[0]+m1[1][1]*m2[1]]

def inv_cross(m1,m2): # Assumes decoding matrix m1 is a 2x2 matrix, and m2 is a 2-array

e = (m1[0][0]*m1[1][1]-m1[0][1]*m1[1][0])

if e == 0: print "Encoding Matrix Not Valid: No inverse matrix."

a,b,c,d = m1[1][1], -m1[0][1], -m1[1][0], m1[0][0]

while a % e != 0: a += 27

while b % e != 0: b += 27

while c % e != 0: c += 27

while d % e != 0: d += 27

return cross([[(a/e),(b/e)],[(c/e),(d/e)]],m2)

def to_int(c):

if c == ' ': return 27

else: return ord(c)-64

def to_chr(i):

i = int(round(i))

if i % 27 == 0: return ' '

else: return chr((i % 27)+64)

f = open("acsl4.in")

for line in f:

try:

strn,res,act,message,key = "", [], True if (line.split(',')[0]=='E') else False, line.split(',')[1].upper(), [[int(line.split(',')[2]),int(line.split(',')[3])],[int(line.split(',')[4]),int(line.split(',')[5])]]

if len(message) % 2 == 1: message += ' '

for i in range(len(message)/2):

if act: res += cross(key,[to_int(message[2*i]),to_int(message[2*i+1])])

else: res += inv_cross(key,[to_int(message[2*i]),to_int(message[2*i+1])])

strn += to_chr(res[2*i]) + to_chr(res[2*i+1])

print strn

except: print "Bad Input or File Not Found. Please check the file to make sure input is formatted properly. Note that the encoding matrix must have a valid inverse (a*d != b*c)."