iOS md5加密（32位小写）

- (NSString *)md5To32bit:(NSString *)input {

    const char* str = [input UTF8String];

    unsigned char result[CC_MD2_DIGEST_LENGTH];

    CC_MD5(str, (CC_LONG)strlen(str), result);

    NSMutableString *ret = [NSMutableString stringWithCapacity:CC_MD5_DIGEST_LENGTH*2];

    for(int i = 0; I<CC_MD2_DIGEST_LENGTH;i++){

        [ret appendFormat:@"%02x",result[i]];

    }

    return ret;

}