我一直在尝试将 Rc4 算法从 objective-c 重写为 swift,以测试苹果(现在已经过时)的说法,关于它运行得更快。 然而,在我得到的这些时间里,一定有什么地方我做错了一些可怕的事情
这是 Objective-C 代码:
+(NSString*)Rc4:(NSString*)aInput key:(NSString *)aKey {
NSMutableArray *iS = [[NSMutableArray alloc] initWithCapacity:256];
NSMutableArray *iK = [[NSMutableArray alloc] initWithCapacity:256];
for (int i = 0; i <256;i++){
[iS addObject:[NSNumber numberWithInt:i]];
}
for(short i=0;i<256;i++){
UniChar c = [aKey characterAtIndex:i%aKey.length];
[iK addObject:[NSNumber numberWithChar:c]];
}
int j=2;
for (int i=0; i<255;i++){
int is = [[iS objectAtIndex:i] intValue];
UniChar ik = (UniChar)[[iK objectAtIndex:i]charValue];
j= (j+is+ik)%256;
NSNumber *temp = [iS objectAtIndex:i];
[iS replaceObjectAtIndex:i withObject:[iS objectAtIndex:j]];
[iS replaceObjectAtIndex:j withObject:temp];
}
int i =0;
j=0;
NSString *result = aInput;
for (short x=0;x<[aInput length]; x++){
i = (i+1)%256;
int is = [[iS objectAtIndex:i]intValue];
j=(j+is)%256;
int is_i = [[iS objectAtIndex:i]intValue];
int is_j = [[iS objectAtIndex:j]intValue];
int t= (is_i+is_j)%256;
int iY = [[iS objectAtIndex:t]intValue];
UniChar ch = (UniChar)[aInput characterAtIndex:x];
UniChar ch_y=ch^iY;
//NSLog(ch);
//NSLog(iY);
result = [result stringByReplacingCharactersInRange:NSMakeRange(x,1) withString:
[NSString stringWithCharacters:&ch_y length:1] ];
}
[iS release];
[iK release];
return result;
}
使用 -O3 编译时运行速度非常快,我得到以下时间:
100 次运行:0.006 秒
带 key :6f7e2a3d744a3b5859725f412f (128bit)
并输入:“MySecretCodeToBeEncryptionSoNobodySeesIt”
这是我尝试使用 Swift 以相同的方式实现它:
extension String {
subscript (i: Int) -> String {
return String(Array(self)[i])
}
}
extension Character {
func unicodeValue() -> UInt32 {
for s in String(self).unicodeScalars {
return s.value
}
return 0
}
}
func Rc4(input:String, key:String)-> String{
var iS = Array(count:256, repeatedValue: 0)
var iK = Array(count:256, repeatedValue: "")
var keyLength = countElements(key)
for var i = 0; i < 256; i++ {
iS[i] = i;
}
for var i = 0; i < 256 ; i++ {
var c = key[i%keyLength]
iK[i] = c;
}
var j = 2
for var i = 0; i < 255; i++ {
var iss = iS[i]
var ik = iK[i]
// transform string to int
var ik_x:Character = Character(ik)
var ikk_xx = Int(ik_x.unicodeValue())
j = (j+iss+ikk_xx)%256;
var temp = iS[i]
iS[i] = iS[j]
iS[j] = temp
}
var i = 0
j=0
var result = input
var eles = countElements(input)
for var x = 0 ; x<eles ; x++ {
i = (i+1)%256
var iss = iS[i]
j = (j+iss)%256
var is_i = iS[i]
var is_j = iS[j]
var t = (is_i+is_j)%256
var iY = iS[t]
var ch = (input[x])
var ch_x:Character = Character(ch)
var ch_xx = Int(ch_x.unicodeValue())
var ch_y = ch_xx^iY
var start = advance(result.startIndex, x)
var end = advance(start,1);
let range = Range(start:start, end:end)
var maybestring = String(UnicodeScalar(ch_y))
result = result.stringByReplacingCharactersInRange(range, withString:maybestring)
}
return result;
}
我已经尝试实现它,所以它看起来尽可能像 objective-c 版本。 然而,这给了我这些可怕的时光,使用 -O
100 次运行:0.5 秒
编辑 代码现在应该使用我发布的扩展方法在 xcode 6.1 中运行。
我从这样的终端运行它:
xcrun swiftc -O Swift.swift -o swift
Swift.swift 是我的文件,swift 是我的可执行文件
最佳答案
通常速度的说法并不真正适用于加密算法,它们更适用于我通常所说的“业务逻辑”。位、字节、16/32/64 位字等的函数通常很难优化。基本上,加密算法旨在对这些数据结构进行密集操作,可以优化的选择相对较少。
以 Java 为例。虽然比大多数解释语言快得多,但它确实无法与 C/C++ 相提并论,更不用说与汇编优化的加密算法相提并论了。大多数相对较小的代数问题也是如此。
为了让事情变得更快,你至少应该使用 explicit numeric types为你的数字。
关于objective-c - Swift RC4 与 Objective-C RC4 性能对比,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/27413149/