What is hashing?
Hashing maps input data to a fixed-length value. A cryptographic hash is designed to be one-way and has no decryption key, but predictable inputs such as email addresses can be guessed, hashed, and compared to identify a match.
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How hashing works
A hash function takes an input and produces a code, often written as a long string of letters and numbers. Even a tiny change to the input creates a completely different code.
Ad platforms commonly use SHA-256 for customer data. Before hashing, details are usually cleaned and standardized, such as trimming spaces and using lowercase email addresses.
How advertising uses it
Platforms use hashed emails and phone numbers for features like Enhanced Conversions, Advanced Matching, and customer list uploads. Both sides hash their data the same way, then compare codes to find matches without exchanging plain details.
Hashing is not a legal shield
Hashed personal data can still count as personal data under many privacy laws. You still need notice, consent where required, and good data handling.
Common questions
Is hashing the same as encryption?
No. Encryption can be reversed with the right key. Cryptographic hashing has no decryption key, but someone can guess possible original values and compare their hashes. Hashing personal identifiers is generally pseudonymization, not a guarantee of anonymity.
Why do hashed emails fail to match?
Usually because the input wasn't standardized first. Extra spaces or capital letters create a different hash, so the platform can't find a match.
Does hashing make data anonymous?
Not completely. Someone with the same email could create the same hash, so regulators often treat hashed identifiers as personal data.
Do I need to hash data myself?
Often the tag, platform tool, or upload feature hashes it for you. If you build a custom integration, check the platform's requirements.
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