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Application & OT Security · Advanced

Unicode Normalization

Converting equivalent Unicode character sequences to a single standard form (NFC, NFD, NFKC or NFKD) before comparison or validation.

Definition

Different code points can render identically or normalize to the same character, enabling bypasses of filters, username collisions and homograph spoofing. Normalizing consistently before validation and uniqueness checks prevents these issues.

Example

Usernames 'admin' with a full-width 'a' and 'admin' collide after NFKC normalization, so registration must normalize first.

Exam tip

Treat Unicode as a canonicalization issue: normalize before validating.

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