iOS RC4 暗号化#
iOS RC4 暗号化の実装では、文字列の生成手順に注意する必要があります。一部の要件では、base64 で暗号化して出力する必要がありますし、他の要件ではバイト配列を 16 進数の文字列に変換して出力する必要がありますので、特に注意が必要です。
以下はコードです：
// RC4暗号化
- (NSString *)rc4Encode:(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]];
}
int j=1;
for (short i=0; i<256; i++) {
UniChar c = [aKey characterAtIndex:i%aKey.length];
[iK addObject:[NSNumber numberWithChar:c]];
}
j=0;
for (int i=0; i<256; 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;
Byte byteBuffer[aInput.length];
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;
// ここに注意が必要です。元のバージョンでは値を取得してから位置を交換していますが、問題があります。位置を先に交換してから値を取得する必要があります！！！
[iS exchangeObjectAtIndex:i withObjectAtIndex:j];
int iY = [[iS objectAtIndex:t] intValue];
UniChar ch = (UniChar)[aInput characterAtIndex:x];
UniChar ch_y = ch^iY;
byteBuffer[x] = ch_y;
}
// バイト配列を16進数の文字列に変換して出力
NSString *resultString = [self stringFromByte:byteBuffer length:aInput.length];
// NSData *adata = [[NSData alloc] initWithBytes:byteBuffer length:aInput.length];
// NSString *string = [adata base64EncodedStringWithOptions:0]; // base64で暗号化した結果を出力
return resultString;
}
// RC4復号化
- (NSString *)rc4Decode:(NSString *)data key:(NSString*)secret{
// 16進数の文字列の場合
NSData *raw = [self ByteDataFromString:data];
// base64で暗号化した後の文字列の場合
// NSData *raw = [[NSData alloc] initWithBase64EncodedString:data options:0];
int cipherLength = (int)raw.length;
UInt8 *cipher = malloc(cipherLength);
[raw getBytes:cipher length:cipherLength];
NSData *kData = [secret dataUsingEncoding:NSUTF8StringEncoding];
int keyLength = (int)kData.length;
UInt8 *kBytes = malloc(kData.length);
[kData getBytes:kBytes length:kData.length];
UInt8 *decipher = malloc(cipherLength + 1);
UInt8 iS[256];
UInt8 iK[256];
int i;
for (i = 0; i < 256; i++){
iS[i] = i;
iK[i] = kBytes[i % keyLength];
}
int j = 0;
for (i = 0; i < 256; i++){
int is = iS[i];
int ik = iK[i];
j = (j + is + ik)% 256;
UInt8 temp = iS[i];
iS[i] = iS[j];
iS[j] = temp;
}
int q = 0;
int p = 0;
for (int x = 0; x < cipherLength; x++){
q = (q + 1)% 256;
p = (p + iS[q])% 256;
int k = iS[p];
iS[p] = iS[q];
iS[q] = k;
k = iS[(iS[q] + iS[p])% 256];
decipher[x] = cipher[x] ^ k;
}
free(kBytes);
decipher[cipherLength] = '\0';
return @((char *)decipher);
}
// バイト配列を文字列に変換
- (NSString *)stringFromByte:(Byte *)byteBuffer length:(NSInteger)length {
NSMutableString *hexString = [[NSMutableString alloc] init];
for (int i = 0; i < length; i++) {
[hexString appendString:[NSString stringWithFormat:@"%0.2hhx", byteBuffer[i]]];
}
return [hexString uppercaseString];
}
- (NSData *)ByteDataFromString:(NSString *)targetStr {
NSInteger len = [targetStr length] / 2; // ターゲットの長さ
unsigned char *buf = malloc(len);
unsigned char *whole_byte = buf;
char byte_chars[3] = {'\0','\0','\0'};
int i;
for (i=0; i < [targetStr length] / 2; i++) {
byte_chars[0] = [targetStr characterAtIndex:i*2];
byte_chars[1] = [targetStr characterAtIndex:i*2+1];
*whole_byte = strtol(byte_chars, NULL, 16);
whole_byte++;
}
NSData *data = [NSData dataWithBytes:buf length:len];
free( buf );
return data;
}