最近项目开发,运用到要获取UUID转MD5,但是iOS7不能使用获取的UDID的接口（涉及到隐私），获取MAC地址的方式的接口在iOS7下也废弃了.目前可能的就是获取UUID了,但是在iOS7下,UUID一个不好的地方是每次调用一次，生成的就不一样，这个会导致一旦APP卸载重装，UUID就变了.

        下面,介绍一种比较方便的方法,来解决这一问题:

         1.导入Security.framework

         2.在github上http://github.com/soffes/sskeychain下载SSKeychain开源库,引入SSKeychain文件夹到你的工程

- (NSString *)getIOSUUID
{
    NSString *retrieveuuid = [SSKeychain passwordForService:@"com.mohe.userinfo"account:@"uuid"];
    
    if ( retrieveuuid == nil || [retrieveuuid isEqualToString:@""]){
        CFUUIDRef uuid = CFUUIDCreate(NULL);
        assert(uuid != NULL);
        CFStringRef uuidStr = CFUUIDCreateString(NULL, uuid);
        
        retrieveuuid = [NSString stringWithFormat:@"%@", uuidStr];
        
        [SSKeychain setPassword:retrieveuuid forService:@"com.mohe.userinfo"account:@"uuid"];
    }
    return retrieveuuid;
}

@转换MD5格式的话可以写个类目:

#import "NSString+MD5.h"
#import <CommonCrypto/CommonDigest.h>
@implementation NSString (MD5)
- (NSString *)md5HexDigest
{
    const char *original_str = [self UTF8String];
    unsigned char result[CC_MD5_DIGEST_LENGTH];
    CC_MD5(original_str, (int)strlen(original_str), result);
    NSMutableString *hash = [NSMutableString string];
    for (int i = 0; i < 16; i++)
        [hash appendFormat:@"%02X", result[i]];
    return [hash lowercaseString];
}
@end