final7appended.py

"""
final7.py  Tristen Wentling    Used to solve problem 7 on final exam
"""
def main():
    nrecip=12074181603861285697    #your public key, n
    erecip=4774715375191615501     #your public key, e
    n_self=2161926180097578217     #my public key, n
    e_self=30216720412799147       #my public key, e
    d_self=402178956129334623      #my public key, d
    encode=True
    textfile=open("ptext1.txt","r") #get text to encrypt from file
    lines=textfile.readlines()
    textfile.close()
    blocklength=8                  #choose letter block length
    pad=len(lines[0])%blocklength  #padding to get multiples of block length chosen
    xs='X'
    for i in xrange(1,pad):
        xs=xs+'X'
    y=lines[0]
    lines[0]=y[:-1]+xs
    splitter=lambda x,y: [ x[i:i+y] for i in xrange(0,len(x),y)]
    splitlist=splitter(lines[0],blocklength) #parse list into length 8 blocks
    if encode==True:
        for i in xrange(len(splitlist)):
            message=list(splitlist[i]) #separates letters
            mess=[]
            for i in xrange(len(message)): #converts to numeric value
                x=getcharval(message[i])
                mess.append(x)
            encmess=rsaencrypt(mess,d_self,n_self) #1st encryption (signing)
            signedmess=rsasigned(encmess,erecip,nrecip) #2nd encryption (your key)
            print signedmess   #prints encoded message
#FUNCTIONS USED ABOVE: 1ST AND 2ND ENCRYPTION, POWERMOD,AND DICTIONARIES
def rsaencrypt(mess,e,n):                       #encrypt with my signing key 
    encnum=str(mess[0])
    for i in xrange(1,len(mess)):
        encnum=encnum+str(mess[i])
    encnum=int(encnum)
    encblock=powermod(encnum,e,n)
    return encblock
    
def rsasigned(encblock,d,n):                    #encrypt with your public key
    signblock=powermod(encblock,d,n)
    return signblock

def getchars(num):   #gets string formatted letter from numeric value
    mydict={0:'A',1:'B',2:'C',3:'D',4:'E',5:'F',6:'G',7:'H',8:'I',9:'J',10:'K',11:'L',12:'M',13:'N',14:'O',15:'P',16:'Q',17:'R',18:'S',19:'T',20:'U',21:'V',22:'W',23:'X',24:'Y',25:'Z'}
    return mydict[num]

def getcharval(letter): #returns numeric value of string formatted letter 
    mydict={'A':0,'B':1,'C':2,'D':3,'E':4,'F':5,'G':6,'H':7,'I':8,'J':9,'K':10,'L':11,'M':12,'N':13,'O':14,'P':15,'Q':16,'R':17,'S':18,'T':19,'U':20,'V':21,'W':22,'X':23,'Y':24,'Z':25}
    return mydict[letter]

def powermod(base,power,modulus):  #faster squaring of a^k (mod n)
    n=modulus
    a=base
    k=power
    binary=list((bin(k)[3:])) #slices off beginning prefix and first '1' of bin number
    result=a
    for i in xrange(len(binary)):
        sqr=lambda x:x**2
        ext=lambda x:(x**2)*a
        p=int(binary[i])
        if p==0:
            result=sqr(result)%n
        else: result=ext(result)%n
    return (result)
main()