NSString类型的的data 怎么转换

string类型的data  比如 @“9bbb413a885a2b6a1b063547aca1d23”  与 正常的NSData  之间相互转换的方法

#pragma mark - 16进制字符串原封转为Data
+ (NSData *)dataForHexString:(NSString *)hexStr {
Byte bytes[hexStr.length/2 + 1];

for (int i = 0; i < hexStr.length/2; i++) {
long intCh;

//high
char high = [hexStr characterAtIndex:2*i];
if (high >= 'a' && high <= 'f')
intCh = ((high - 'a') + 10)*16;
else
intCh = (high - '0')*16;

//low
char low = [hexStr characterAtIndex:2*i + 1];
if (low >= 'a')
intCh += ((low - 'a') + 10);
else
intCh += (low - '0');

bytes[i] = intCh;
}

NSData *data = [NSData dataWithBytes:bytes length:hexStr.length/2];
return data;
}

#pragma mark - Data原封转为16进制字符串
+ (NSString *)stringForData:(NSData *)data {
NSString *reslutStr = @"";
Byte *bytes = (Byte *)data.bytes;
for (NSInteger i = 0; i < data.length; i++) {
reslutStr = [reslutStr stringByAppendingString:[NSString stringWithFormat:@"%x",bytes[i]]];
}
return reslutStr;
}