Providing Hashed Data

Hashing is a form of one-way encryption, meaning once data is hashed, there is no way back to its raw form. If the data is “hashed” using the same method, it will always produce the same result, allowing you to safely transfer data to advertising platforms (like Meta) while lowering the risk to your users of exposing their unencrypted personal details.

Thirty-One Circles can take unencrypted data and complete the hashing step for you, or for email addresses, you can provide already hashed data. If you choose to send hashed email data to the platform, you must follow the steps below, as it is impossible to fix (or indeed know if it has been done correctly) once hashed.

For emails:

  • Lowercase all characters in the email
  • Remove all surrounding whitespace
  • DO NOT add any form of “salt” to the email string
  • Use a SHA256 algorithm to perform the hash.

After hashing we recommend you perform a quick check that the "hashed email" is exactly 64 characters long. 

For phone numbers:

We do not accept hashed data for phone numbers as different advertising platforms require varied normalisation processes pre-hashing.


We recommend that you perform the hashing step only if you are confident the correct normalisation steps have been conducted. If they are not your data will have an extremely low match rate.

More questions?

Contact our support team at who are always ready to offer advice and assistance.