DES加密问题 。。大牛们帮帮忙

Question

字符长度在《＝300加密是成功的。   如果字符串的长度>300 ，那么DES加密只能加密 <=300以内的。 多出来的字符串长度就没有加密。直接丢失
请问各位大牛们｀ 如果我要加密<2000长度的DES加密方法要怎么写好呢
 ／／  这个是我的加密方法
+(int)convertToInt:(NSString*)strtemp {
    //计算中文和英文的混合长度
    
    int strlength = 0;
    char* p = (char*)[strtemp cStringUsingEncoding:NSUnicodeStringEncoding];
    for (int i=0 ; i<[strtemp lengthOfBytesUsingEncoding:NSUnicodeStringEncoding] ;i++) {
        if (*p) {
            p++;
            strlength++;
        }
        else {
            p++;
        }
    }
    return (strlength+1)/2;
    
}
+ (NSString *) encryptUseDES:(NSString *)plainText key:(NSString *)key
{    
    NSString *encryptStr;
    const char *textBytes = [plainText UTF8String];
    NSUInteger dataLength =[self convertToInt:plainText];
    unsigned char buffer[1024];
    memset(buffer, 0, sizeof(char));
    size_t numBytesEncrypted = 0;    CCCryptorStatus cryptStatus = CCCrypt(kCCEncrypt, kCCAlgorithmDES,
                                          kCCOptionPKCS7Padding,
                                          [key UTF8String], kCCKeySizeDES,
                                          IV,
                                          textBytes, dataLength,
                                          buffer, 1024,
                                          &numBytesEncrypted);
    if (cryptStatus == kCCSuccess) {
        
        NSData *data = [NSData dataWithBytes:buffer length:(NSUInteger)numBytesEncrypted];
        encryptStr = [[NSString alloc] initWithData:[GTMBase64 encodeData:data] encoding:NSUTF8StringEncoding];    }
    return encryptStr;}+ (NSString *) decryptUseDES:(NSString*)cipherText key:(NSString*)key
{
    NSString* decryptStr;
    NSData* cipherData = [GTMBase64 decodeString:cipherText];
    unsigned char buffer[1024];
    memset(buffer, 0, sizeof(char));
    size_t numBytesDecrypted = 0;
    CCCryptorStatus cryptStatus = CCCrypt(kCCDecrypt,
                                          kCCAlgorithmDES,
                                          kCCOptionPKCS7Padding,
                                          [key UTF8String],
                                          kCCKeySizeDES,
                                          IV,
                                          [cipherData bytes],
                                          [cipherData length],
                                          buffer,
                                          1024,
                                          &numBytesDecrypted);
    if (cryptStatus == kCCSuccess) {
        NSData* data = [NSData dataWithBytes:buffer length:(NSUInteger)numBytesDecrypted];
        decryptStr = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
    }
    return decryptStr;
    
    
}

Answer 1

unsigned char buffer[1024];
memset(buffer, 0, sizeof(char));
这个buffer的长度有问题，如果这样写死(1024),意思就是加密后的数据最多只能1024.正确的写法是根据输入数据的长度来确定输出的长度
size_t  dataOutLen = (dataInLength + kCCBlockSizeDES) & ~(kCCBlockSizeDES - 1);  
void *dataOut = malloc( dataOutLen * sizeof(uint8_t));