🧶Skein

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A flexible SHA-3 candidate hash function family built on the Threefish tweakable block cipher, supporting tree hashing and personalization.

DESCRIPTION

Skein is a cryptographic hash function suite submitted to the NIST SHA-3 competition. It uses the Threefish tweakable block cipher as its core and supports features like tree hashing, personalization strings, and optional arguments for domain separation. While Skein was not selected as SHA-3, its design influenced modern hash features and research. Today, SHA-2/3 and BLAKE2/BLAKE3 are more common in production.

ALTERNATIVE DEFINITIONS

Bruce Schneier

Skein is a cryptographic hash function based on the Threefish tweakable block cipher, designed for the NIST SHA-3 competition.

Designer-maintained project page; paraphrased due to offline generation.

Source

NIST

Skein was one of the candidates evaluated in the SHA-3 competition process.

Places Skein in the standardization context; paraphrased due to offline generation.

Source

RELATED TERMS

Threefish SHA-3 BLAKE Whirlpool Tree hashing Personalization Cryptographic Hash Function XOF Domain Separation

COMPETING TERMS

Keccak

KNOWLEDGE AREAS

Data Security Software Engineering

TARGET AUDIENCE

Security Architect Cybersecurity Engineer Software Developer DevOps Engineer IT Auditor

EXTERNAL SOURCES

• Wikipedia - Skein (hash function)
• Bruce Schneier - Official Skein project page.
• NIST - SHA-3 candidate portfolio.
• IACR ePrint - Skein design and analysis paper.

TOP QUESTIONS

What makes Skein unique?

It is built on a tweakable block cipher (Threefish) and supports features like tree hashing and personalization for flexible use.

Category: Distinction

Why wasn’t Skein selected as SHA-3?

Keccak was chosen for its sponge construction and overall security-performance profile; Skein remained a respected finalist.

Category: Background

Is Skein still relevant?

It’s relevant academically and for certain implementations, though most production systems use SHA-2, SHA-3, or BLAKE2/3.

Category: Relevancy

Does Skein support extendable output?

Skein includes features enabling variable output and domain separation via optional arguments.

Category: Definition

Where can I find Skein reference material?

The official project page and IACR papers detail the design and performance characteristics.

Category: Resources

Is Skein standardized?

No NIST standard exists for Skein; Keccak became SHA-3.

Category: Standards

What performance does Skein offer?

Skein aimed for high performance on modern CPUs, benefiting from Threefish’s simple operations.

Category: Performance

Can I use Skein for HMAC?

Yes, HMAC can be constructed over Skein, but HMAC-SHA-256/512 is more widely supported.

Category: Application

Who designed Skein?

A team including Bruce Schneier, Niels Ferguson, and Stefan Lucks designed Skein.

Category: People