RC4文件加密的python实现方法

# for python 3.0
# from 李勃
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''
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''
#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()