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Security Fundamentals & Crypto · Foundational

Secure Hash Algorithm 1 (SHA-1)

Legacy 160-bit hash function with practical collision attacks; deprecated for security use.

Definition

SHA-1 was published in 1995 and widely used in certificates and Git. Google's SHAttered attack produced a practical collision in 2017. Browsers no longer trust SHA-1 certificates, and NIST plans to retire SHA-1 entirely by the end of 2030.

Example

Two different PDF files with the same SHA-1 hash were published in the SHAttered research.

Exam tip

SHA-1 = 160-bit digest; know it is deprecated for signatures.

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