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// OpenUDID.m
// openudid
// initiated by Yann Lechelle (cofounder @Appsfire) on 8/28/11.
// Copyright 2011
// Initiators/root branches
// iOS code:
// Android code:
// Contributors:
This software is provided 'as-is', without any express or implied
warranty. In no event will the authors be held liable for any damages
arising from the use of this software.
Permission is granted to anyone to use this software for any purpose,
including commercial applications, and to alter it and redistribute it
freely, subject to the following restrictions:
1. The origin of this software must not be misrepresented; you must not
claim that you wrote the original software. If you use this software
in a product, an acknowledgment in the product documentation would be
appreciated but is not required.
2. Altered source versions must be plainly marked as such, and must not be
misrepresented as being the original software.
3. This notice may not be removed or altered from any source
#if __has_feature(objc_arc)
#error This file uses the classic non-ARC retain/release model; hints below...
// to selectively compile this file as non-ARC, do as follows:
#import "OpenUDID.h"
#import <CommonCrypto/CommonDigest.h> // Need to import for CC_MD5 access
#import <UIKit/UIPasteboard.h>
#import <UIKit/UIKit.h>
#import <AppKit/NSPasteboard.h>
#define OpenUDIDLog(fmt, ...)
//#define OpenUDIDLog(fmt, ...) NSLog((@"%s [Line %d] " fmt), __PRETTY_FUNCTION__, __LINE__, ##__VA_ARGS__);
//#define OpenUDIDLog(fmt, ...) NSLog((@"[Line %d] " fmt), __LINE__, ##__VA_ARGS__);
static NSString * kOpenUDIDSessionCache = nil;
static NSString * const kOpenUDIDKey = @"OpenUDID";
static NSString * const kOpenUDIDSlotKey = @"OpenUDID_slot";
static NSString * const kOpenUDIDAppUIDKey = @"OpenUDID_appUID";
static NSString * const kOpenUDIDTSKey = @"OpenUDID_createdTS";
static NSString * const kOpenUDIDOOTSKey = @"OpenUDID_optOutTS";
static NSString * const kOpenUDIDDomain = @"org.OpenUDID";
static NSString * const kOpenUDIDSlotPBPrefix = @"org.OpenUDID.slot.";
static int const kOpenUDIDRedundancySlots = 100;
@interface OpenUDID (Private)
+ (void) _setDict:(id)dict forPasteboard:(id)pboard;
+ (NSMutableDictionary*) _getDictFromPasteboard:(id)pboard;
+ (NSString*) _generateFreshOpenUDID;
@implementation OpenUDID
// Archive a NSDictionary inside a pasteboard of a given type
// Convenience method to support iOS & Mac OS X
+ (void) _setDict:(id)dict forPasteboard:(id)pboard {
[pboard setData:[NSKeyedArchiver archivedDataWithRootObject:dict] forPasteboardType:kOpenUDIDDomain];
[pboard setData:[NSKeyedArchiver archivedDataWithRootObject:dict] forType:kOpenUDIDDomain];
// Retrieve an NSDictionary from a pasteboard of a given type
// Convenience method to support iOS & Mac OS X
+ (NSMutableDictionary*) _getDictFromPasteboard:(id)pboard {
id item = [pboard dataForPasteboardType:kOpenUDIDDomain];
id item = [pboard dataForType:kOpenUDIDDomain];
if (item) {
item = [NSKeyedUnarchiver unarchiveObjectWithData:item];
} @catch(NSException* e) {
OpenUDIDLog(@"Unable to unarchive item %@ on pasteboard!", [pboard name]);
item = nil;
// return an instance of a MutableDictionary
return [NSMutableDictionary dictionaryWithDictionary:(item == nil || [item isKindOfClass:[NSDictionary class]]) ? item : nil];
// Private method to create and return a new OpenUDID
// Theoretically, this function is called once ever per application when calling [OpenUDID value] for the first time.
// After that, the caching/pasteboard/redundancy mechanism inside [OpenUDID value] returns a persistent and cross application OpenUDID
+ (NSString*) _generateFreshOpenUDID {
NSString* _openUDID = nil;
// August 2011: One day, this may no longer be allowed in iOS. When that is, just comment this line out.
// March 25th 2012: this day has come, let's remove this "outlawed" call...
// if([UIDevice instancesRespondToSelector:@selector(uniqueIdentifier)]){
// _openUDID = [[UIDevice currentDevice] uniqueIdentifier];
// }
// Next we try to use an alternative method which uses the host name, process ID, and a time stamp
// We then hash it with md5 to get 32 bytes, and then add 4 extra random bytes
// Collision is possible of course, but unlikely and suitable for most industry needs (e.g.. aggregate tracking)
if (_openUDID==nil) {
unsigned char result[16];
const char *cStr = [[[NSProcessInfo processInfo] globallyUniqueString] UTF8String];
CC_MD5( cStr, strlen(cStr), result );
_openUDID = [NSString stringWithFormat:
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],
arc4random() % 4294967295];
// Call to other developers in the Open Source community:
// feel free to suggest better or alternative "UDID" generation code above.
// NOTE that the goal is NOT to find a better hash method, but rather, find a decentralized (i.e. not web-based)
// 160 bits / 20 bytes random string generator with the fewest possible collisions.
return _openUDID;
// Main public method that returns the OpenUDID
// This method will generate and store the OpenUDID if it doesn't exist, typically the first time it is called
// It will return the null udid (forty zeros) if the user has somehow opted this app out (this is subject to 3rd party implementation)
// Otherwise, it will register the current app and return the OpenUDID
+ (NSString*) value {
return [self valueWithError:nil];
+ (NSString*) valueWithError:(NSError **)error {
if (kOpenUDIDSessionCache!=nil) {
if (error!=nil)
*error = [NSError errorWithDomain:kOpenUDIDDomain
userInfo:[NSDictionary dictionaryWithObjectsAndKeys:@"OpenUDID in cache from first call",@"description", nil]];
return kOpenUDIDSessionCache;
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
// The AppUID will uniquely identify this app within the pastebins
NSString * appUID = (NSString *) [defaults objectForKey:kOpenUDIDAppUIDKey];
if(appUID == nil)
// generate a new uuid and store it in user defaults
CFUUIDRef uuid = CFUUIDCreate(NULL);
appUID = (NSString *) CFUUIDCreateString(NULL, uuid);
NSString* openUDID = nil;
NSString* myRedundancySlotPBid = nil;
NSDate* optedOutDate = nil;
BOOL optedOut = NO;
BOOL saveLocalDictToDefaults = NO;
BOOL isCompromised = NO;
// Do we have a local copy of the OpenUDID dictionary?
// This local copy contains a copy of the openUDID, myRedundancySlotPBid (and unused in this block, the local bundleid, and the timestamp)
id localDict = [defaults objectForKey:kOpenUDIDKey];
if ([localDict isKindOfClass:[NSDictionary class]]) {
localDict = [NSMutableDictionary dictionaryWithDictionary:localDict]; // we might need to set/overwrite the redundancy slot
openUDID = [localDict objectForKey:kOpenUDIDKey];
myRedundancySlotPBid = [localDict objectForKey:kOpenUDIDSlotKey];
optedOutDate = [localDict objectForKey:kOpenUDIDOOTSKey];
optedOut = optedOutDate!=nil;
OpenUDIDLog(@"localDict = %@",localDict);
// Here we go through a sequence of slots, each of which being a UIPasteboard created by each participating app
// The idea behind this is to both multiple and redundant representations of OpenUDIDs, as well as serve as placeholder for potential opt-out
NSString* availableSlotPBid = nil;
NSMutableDictionary* frequencyDict = [NSMutableDictionary dictionaryWithCapacity:kOpenUDIDRedundancySlots];
for (int n=0; n<kOpenUDIDRedundancySlots; n++) {
NSString* slotPBid = [NSString stringWithFormat:@"%@%d",kOpenUDIDSlotPBPrefix,n];
UIPasteboard* slotPB = [UIPasteboard pasteboardWithName:slotPBid create:NO];
NSPasteboard* slotPB = [NSPasteboard pasteboardWithName:slotPBid];
OpenUDIDLog(@"SlotPB name = %@",slotPBid);
if (slotPB==nil) {
// assign availableSlotPBid to be the first one available
if (availableSlotPBid==nil) availableSlotPBid = slotPBid;
} else {
NSDictionary* dict = [self _getDictFromPasteboard:slotPB];
NSString* oudid = [dict objectForKey:kOpenUDIDKey];
OpenUDIDLog(@"SlotPB dict = %@",dict);
if (oudid==nil) {
// availableSlotPBid could inside a non null slot where no oudid can be found
if (availableSlotPBid==nil) availableSlotPBid = slotPBid;
} else {
// increment the frequency of this oudid key
int count = [[frequencyDict valueForKey:oudid] intValue];
[frequencyDict setObject:[NSNumber numberWithInt:++count] forKey:oudid];
// if we have a match with the app unique id,
// then let's look if the external UIPasteboard representation marks this app as OptedOut
NSString* gid = [dict objectForKey:kOpenUDIDAppUIDKey];
if (gid!=nil && [gid isEqualToString:appUID]) {
myRedundancySlotPBid = slotPBid;
// the local dictionary is prime on the opt-out subject, so ignore if already opted-out locally
if (optedOut) {
optedOutDate = [dict objectForKey:kOpenUDIDOOTSKey];
optedOut = optedOutDate!=nil;
// sort the Frequency dict with highest occurence count of the same OpenUDID (redundancy, failsafe)
// highest is last in the list
NSArray* arrayOfUDIDs = [frequencyDict keysSortedByValueUsingSelector:@selector(compare:)];
NSString* mostReliableOpenUDID = (arrayOfUDIDs!=nil && [arrayOfUDIDs count]>0)? [arrayOfUDIDs lastObject] : nil;
OpenUDIDLog(@"Freq Dict = %@\nMost reliable %@",frequencyDict,mostReliableOpenUDID);
// if openUDID was not retrieved from the local preferences, then let's try to get it from the frequency dictionary above
if (openUDID==nil) {
if (mostReliableOpenUDID==nil) {
// this is the case where this app instance is likely to be the first one to use OpenUDID on this device
// we create the OpenUDID, legacy or semi-random (i.e. most certainly unique)
openUDID = [self _generateFreshOpenUDID];
} else {
// or we leverage the OpenUDID shared by other apps that have already gone through the process
openUDID = mostReliableOpenUDID;
// then we create a local representation
if (localDict==nil) {
localDict = [NSMutableDictionary dictionaryWithCapacity:4];
[localDict setObject:openUDID forKey:kOpenUDIDKey];
[localDict setObject:appUID forKey:kOpenUDIDAppUIDKey];
[localDict setObject:[NSDate date] forKey:kOpenUDIDTSKey];
if (optedOut) [localDict setObject:optedOutDate forKey:kOpenUDIDTSKey];
saveLocalDictToDefaults = YES;
else {
// Sanity/tampering check
if (mostReliableOpenUDID!=nil && ![mostReliableOpenUDID isEqualToString:openUDID])
isCompromised = YES;
// Here we store in the available PB slot, if applicable
OpenUDIDLog(@"Available Slot %@ Existing Slot %@",availableSlotPBid,myRedundancySlotPBid);
if (availableSlotPBid!=nil && (myRedundancySlotPBid==nil || [availableSlotPBid isEqualToString:myRedundancySlotPBid])) {
UIPasteboard* slotPB = [UIPasteboard pasteboardWithName:availableSlotPBid create:YES];
[slotPB setPersistent:YES];
NSPasteboard* slotPB = [NSPasteboard pasteboardWithName:availableSlotPBid];
// save slotPBid to the defaults, and remember to save later
if (localDict) {
[localDict setObject:availableSlotPBid forKey:kOpenUDIDSlotKey];
saveLocalDictToDefaults = YES;
// Save the local dictionary to the corresponding UIPasteboard slot
if (openUDID && localDict)
[self _setDict:localDict forPasteboard:slotPB];
// Save the dictionary locally if applicable
if (localDict && saveLocalDictToDefaults)
[defaults setObject:localDict forKey:kOpenUDIDKey];
// If the UIPasteboard external representation marks this app as opted-out, then to respect privacy, we return the ZERO OpenUDID, a sequence of 40 zeros...
// This is a *new* case that developers have to deal with. Unlikely, statistically low, but still.
// To circumvent this and maintain good tracking (conversion ratios, etc.), developers are invited to calculate how many of their users have opted-out from the full set of users.
// This ratio will let them extrapolate convertion ratios more accurately.
if (optedOut) {
if (error!=nil) *error = [NSError errorWithDomain:kOpenUDIDDomain
userInfo:[NSDictionary dictionaryWithObjectsAndKeys:[NSString stringWithFormat:@"Application with unique id %@ is opted-out from OpenUDID as of %@",appUID,optedOutDate],@"description", nil]];
kOpenUDIDSessionCache = [[NSString stringWithFormat:@"%040x",0] retain];
return kOpenUDIDSessionCache;
// return the well earned openUDID!
if (error!=nil) {
if (isCompromised)
*error = [NSError errorWithDomain:kOpenUDIDDomain
userInfo:[NSDictionary dictionaryWithObjectsAndKeys:@"Found a discrepancy between stored OpenUDID (reliable) and redundant copies; one of the apps on the device is most likely corrupting the OpenUDID protocol",@"description", nil]];
*error = [NSError errorWithDomain:kOpenUDIDDomain
userInfo:[NSDictionary dictionaryWithObjectsAndKeys:@"OpenUDID succesfully retrieved",@"description", nil]];
kOpenUDIDSessionCache = [openUDID retain];
return kOpenUDIDSessionCache;
+ (void) setOptOut:(BOOL)optOutValue {
// init call
[self value];
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
// load the dictionary from local cache or create one
id dict = [defaults objectForKey:kOpenUDIDKey];
if ([dict isKindOfClass:[NSDictionary class]]) {
dict = [NSMutableDictionary dictionaryWithDictionary:dict];
} else {
dict = [NSMutableDictionary dictionaryWithCapacity:2];
// set the opt-out date or remove key, according to parameter
if (optOutValue)
[dict setObject:[NSDate date] forKey:kOpenUDIDOOTSKey];
[dict removeObjectForKey:kOpenUDIDOOTSKey];
// store the dictionary locally
[defaults setObject:dict forKey:kOpenUDIDKey];
OpenUDIDLog(@"Local dict after opt-out = %@",dict);
// reset memory cache
kOpenUDIDSessionCache = nil;
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