How does anonymization or pseudonymization apply to phone number data?

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Anonymization and pseudonymization are two distinct but related techniques used to protect privacy by de-identifying personal data, including phone numbers. Understanding their differences is crucial for compliance with privacy regulations like GDPR, which encourages their use.

Pseudonymization
Definition: Pseudonymization is the processing of poland number database personal data in such a manner that the personal data can no longer be attributed to a specific data subject without the use of additional information, provided that such additional information is kept separately and is subject to technical and organizational measures to ensure that the personal data are not attributed to an identified or identifiable natural person.

How it applies to phone numbers:
With pseudonymization, a phone number is replaced with a unique, artificial identifier (a pseudonym or token). This pseudonym allows the data to be used for analysis, testing, or other purposes while reducing the immediate risk of direct identification. However, the original phone number can be re-identified if the "key" or "linking table" that maps the pseudonym back to the original number is accessed.

Common techniques for phone numbers:

Tokenization/Hashing:
Hashing: The phone number is run through a cryptographic hash function (e.g., SHA-256). This produces a fixed-length string of characters (the hash value) that is unique to the original phone number. While theoretically irreversible (one-way), robust hashing with salting can make it more secure.
Tokenization: The phone number is replaced with a randomly generated token. The original number is stored securely in a separate vault or database, linked to the token. This allows for reversible de-identification when needed.
Sequential or Random ID Assignment: Replacing actual phone numbers with sequential IDs (e.g., "User001", "User002") or randomly generated alphanumeric strings. The mapping between the ID and the real phone number is stored separately.
Data Masking/Substitution: Replacing parts of the phone number with generic characters (e.g., replacing the last few digits with "XXX") or substituting