+(NSString *)createMD5:(NSString *)signString
{
    const char*cStr =[signString UTF8String];
    unsigned char result[16];
    CC_MD5(cStr, strlen(cStr), result);
    return[NSString stringWithFormat:
           @"%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X%02X",
           result[0], result[1], result[2], result[3],
           result[4], result[5], result[6], result[7],
           result[8], result[9], result[10], result[11],
           result[12], result[13], result[14], result[15]
           ];
}
 

+(NSString*) md5:(NSString*) str
{  
    const char *cStr = [str UTF8String];  
    unsigned char result[CC_MD5_DIGEST_LENGTH];  
    CC_MD5( cStr, strlen(cStr), result );  
    
    NSMutableString *hash = [NSMutableString string];
    for(int i=0;i<CC_MD5_DIGEST_LENGTH;i++)
    {
        [hash appendFormat:@"%02X",result[i]];
    }
    return [hash lowercaseString];
}
#define CHUNK_SIZE 1024  
+(NSString *)file_md5:(NSString*) path
{  
    NSFileHandle* handle = [NSFileHandle fileHandleForReadingAtPath:path];  
    if(handle == nil)  
        return nil;  
    
    CC_MD5_CTX md5_ctx;  
    CC_MD5_Init(&md5_ctx);  
    
    NSData* filedata;  
    do {  
        filedata = [handle readDataOfLength:CHUNK_SIZE];  
        CC_MD5_Update(&md5_ctx, [filedata bytes], [filedata length]);  
    }  
    while([filedata length]);  
    
    unsigned char result[CC_MD5_DIGEST_LENGTH];  
    CC_MD5_Final(result, &md5_ctx);  
    
    [handle closeFile];  
    
    NSMutableString *hash = [NSMutableString string];
    for(int i=0;i<CC_MD5_DIGEST_LENGTH;i++)
    {
        [hash appendFormat:@"%02x",result[i]];
    }
    return [hash lowercaseString];
}