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SHA-1

A 160-bit hash function published by NIST in 1995, now broken for collision resistance and disallowed in TLS certificates since 2017.

SHA-1 (Secure Hash Algorithm 1) produces a 160-bit digest. It was the default web hash for over a decade but Google and CWI Amsterdam demonstrated a practical collision (SHAttered) in 2017. Browsers stopped trusting SHA-1 TLS certificates that same year, and CAs no longer issue them. SHA-1 lingers in legacy protocols (Git object IDs, older TLS HMAC suites, some DNSSEC NSEC3 deployments) and remains acceptable for non-cryptographic integrity checking. New designs should use SHA-256 or SHA-3.

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