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Concepts
HMAC
Cryptographic seal on a URL or message — proves it's authentic and unmodified
Definition
Hash-based Message Authentication Code. A short signature (SHA-256) over (data + secret-key) that anyone can verify but only the key-holder can generate. We use it on /alerts/ URLs so signed links can't be tampered with or forged. TTL 1 year.
Context anchor
HMAC-SHA256 = 64 hex chars (~256 bits); brute-force ~10^77 attempts — practically unbreakable
Example
Premium alert links carry HMAC signature — proves the URL came from us, not forged
Also known as
hmachmac signaturesigned linkrequest signature