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Editorial Team
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Asked: 2026-05-28T04:29:42+00:00

I have a database of users that are identified by their device udid (which

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I have a database of users that are identified by their device udid (which got deprecated in iOS 5). I need a new way to identify devices that will not generate strings that already exist in my database.

The udid used to be SHA1(SerialNumber + IMEI + WiFiAddress + BluetoothAddress).

Is it safe to use the output of something like MD5(MACAddress) as my new way to identify devices? From what I’ve read it seems like MD5 and SHA-1 output different lengths of strings (respectively 128 and 160 bits), but I’m just making sure I’m not missing anything here. I really don’t want to end up with duplicate identifiers…

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  1. Editorial Team

    Just use SHA1(MAC | 0001) instead of the previous one. The chance of creating a SHA1 that already exists is unlikely to the extreme, as it would indicate a real problem in the SHA1 algorithm (a collision). Note: I presume that + means concatenation, I’ve used | as concatenation.

    You can increase the counter (in characters or something else, try for 4 bytes) at the end if you need another unique identifier.

    Although MD5 is probably safe enough for this purpose, I would still try and avoid the use of this broken hash – just keep with SHA1 (or move to SHA-256).

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