RC4 with Python

import struct,sys,os,binascii

"""
    RC4加密算法
    16*16 S盒
    加密单元:short
"""
def RC4(pkey,keylen,pin,dlen):
    N=65536
    S = list(range(N))
    j = 0
    for i in range(N):
        j = (j + S[i] + pkey[i%keylen])%N
        temp = S[i]
        S[i] = S[j]
        S[j] = temp
    i = j = 0
    pout= b''
    for x in range(dlen):
        i = i+1
        j = (j + S[i])%N
        temp = S[i]
        S[i] = S[j]
        S[j] = temp
        pout += struct.pack('H',pin[x]^S[(S[i]+S[j])%N])
    return(pout)

# bytes->short
def coding(data):
    if(len(data)%2):
        data+=b'\0'
    dlen = len(data)//2
    return(struct.unpack(str(dlen)+'H',data))

# short->bytes
def unCoding(data):
    d=b''
    for i in range(len(data)):
        d += struct.pack('H',data[i])
    return(d)

#产生32字节密钥
def CreaTKEy(Keyt):
    pl = len(Keyt)
    Key=b''
    r=0
    for i in range(32):
        k=(Keyt[r%pl]+i)%256
        Key+= struct.pack('B',k)
        r+=1
    return Key

#更新密钥
def UpdataKey(Keyt):
    Key = unCoding(Keyt)
    #循环左移
    Key = Key[1:] +  struct.pack('B',Key[0])
    tem=0
    #求和
    for i in range(len(Key)):
        tem += Key[i];
    Keyo=b''
    #Xor
    for i in range(len(Key)):
        Keyo += struct.pack('B',(Key[i]^tem)%256)
        tem += Keyo[i]>>3
        tem = tem % 256
    return(Coding(Keyo))

if __name__ == '__main__':

    #获得输入文件
    if len(sys.argv)==1:
        filename = input('源文件: ')
    else:
        filename = sys.argv[1]
      
    try:
        fin = open(filename,'rb')
    except:
        print('打开文件失败！')
        input()
        sys.exit()
    print(filename)

    #打开输出文件
    if filename[-4:]=='.RC4':
        eID = 1
        key=input('输入解密密钥: ').encode()
        ofilename = filename[:-4]
    else:
        eID = 2
        key=input('输入加密密钥: ').encode()
        ofilename = filename+'.RC4'

    key = Coding(CreatKey(key))
    key = UpdataKey(key)
  
    #处理重名
    while os.path.exists(ofilename):
        ofilename = os.path.dirname(ofilename)+ '\\副本 '+ os.path.basename(ofilename)
    fout = open(ofilename,'wb')
    print(ofilename)

    #解密
    if eID==1:
        #读文件长度
        filelen = struct.unpack('I',fin.read(4))[0]
        print('FlieLen =',filelen,'\n......')
        while 1:
            #读块大小
            ps= fin.read(2)
            if not ps:
                #文件结束
                break
            packsize = struct.unpack('H',ps)[0]
            #读数据
            dd=fin.read(packsize)
            #解密
            dd=Coding(dd)
            x = RC4(key,len(key),dd,len(dd))
            key = UpdataKey(key)
            #crc
            crc = struct.unpack('I',fin.read(4))[0]
            if binascii.crc32(x)!=crc:
                print('CRC32校验错误！',crc,binascii.crc32(x))
                input()
                sys.exit()
            fout.write(x)
        #裁剪末尾填充位
        fout.truncate(filelen)
    #加密
    elif eID==2:
        #获得文件长度
        fin.seek(0,2)
        filelen = fin.tell()
        print('FlieLen =',filelen,'\n......')
        fin.seek(0,0)
        fout.write(struct.pack('I',filelen))
        while 1:
            #读数据
            dd=fin.read(65534)
            if not dd:
                #文件结束
                break
            #末尾填充
            srl = len(dd)
            if srl%2:
                srl+=1;
                dd+=b'\0'
            #crc
            crc = struct.pack('I',binascii.crc32(dd))
            #加密数据
            dd=Coding(dd)
            x = RC4(key,len(key),dd,len(dd))
            key = UpdataKey(key)
            #写入文件
            fout.write(struct.pack('H',srl))
            fout.write(x)
            fout.write(crc)
    fin.close()
    fout.close()

    print('OK!')
    input()