Notes

SHA-256 as a source of chance

JAEV Notes · October 2026 · 2 min read

Three grids of 16 by 16 small squares. The first two show the 256 bits of the SHA-256 hashes of the texts JAEV and JAEW, black for 1 and empty for 0, with the hashes in hexadecimal printed below. The third, in red, marks the 131 bits that differ between them.
Diagram by JAEV: two spellings, two hashes. The first grid is the SHA-256 hash of the word JAEV, the second of JAEW, each as 256 squares (black for 1, empty for 0). Only the last letter differs, yet 131 of the 256 squares change: they are red in the third grid. CC BY 4.0.

SHA-256 is a hash function: it turns any text or file into a number 256 bits long. It belongs to the SHA-2 family, designed by the United States National Security Agency and first published in 2001.1 It was made for security, but its output looks random while being completely fixed by its input, so artists use it as a source of chance that can be repeated.

What the function does

The current standard, FIPS 180-4 from the US National Institute of Standards and Technology, describes hash algorithms that produce a "digest" of a message, so that anyone can check whether the message has been changed since.2 Whatever goes in, a single word or a whole film, SHA-256 gives back 256 bits, usually written as 64 hexadecimal digits.1, 3

Two properties make it useful outside cryptography:

  • The same input always gives the same output. There is no hidden state, and no clock is involved.
  • A small change gives a completely different output. If one bit of the input is flipped, about half of the output bits change: the avalanche effect, a term the cryptographer Horst Feistel first used in 1973.4

Together this means the hash behaves like a dice roll that can be rolled again with exactly the same result.

From hash to choices

A generative program reads the 256 bits as 32 numbers from 0 to 255 (one per byte) and lets each one decide something: how many shapes, which kind, which colour, where. The sketch below does that with the text you type.

Sketch by JAEV: the SHA-256 hash of the text, computed in your browser with crypto.subtle.digest, chooses the number of shapes, their kind, colour, symmetry and placement. "New drawing" changes one letter and counts how many of the 256 bits change. A simplified illustration of the method, not the program behind any JAEV work. Code CC BY 4.0.

On the platform Art Blocks, each work's script is given a 32-byte hash as its seed, and the documentation tells artists: "This is your only randomness source." The same hash must always produce the same image.5 SHA-256 is also the function behind proof of work in Bitcoin, explained in the note on Bitcoin's difficulty.1

Where to see it

JAEV's own work Content makes one image a day from a short text recording what the world paid most attention to the day before. The text is turned into a fingerprint, its SHA-256 hash, and the hash makes one choice in each of seven parts of the work: composition, shape, edge, colours, movement, symmetry and layers. The same text always gives the same work.6, 7 Each work's page prints the hash and the seven choices it made.7

Sources

  1. “SHA-2”. Wikipedia
    “designed by the United States National Security Agency (NSA) and first published in 2001”; SHA-256 gives a 256-bit digest; “Several cryptocurrencies, including Bitcoin, use SHA-256 for verifying transactions and calculating proof of work.”
  2. FIPS 180-4, Secure Hash Standard (SHS). National Institute of Standards and Technology, August 2015
    “This standard specifies hash algorithms that can be used to generate digests of messages. The digests are used to detect whether messages have been changed since the digests were generated.”
  3. “SubtleCrypto: digest() method”. MDN Web Docs, Mozilla
    “A digest is a short fixed-length value derived from some variable-length input.” “Cryptographic digests should exhibit collision-resistance.” SHA-256: 256 bits.
  4. “Avalanche effect”. Wikipedia
    Flipping one input bit changes about half the output bits; the strict avalanche criterion: each output bit changes with a 50% probability; term first used by Horst Feistel (1973).
  5. “1. Building Your Project”. Art Blocks documentation
    “tokenData.hash is a 32-byte hex string — the unique, on-chain random seed for this token.” “This is your only randomness source.” “Same hash → same output, always”.
  6. “Content”, JAEV. JAEV, Lund
    “The text is turned into a fingerprint, a long number that changes completely if a single character changes. The number makes one choice in each of seven parts of the work … The same text always gives the same work.”
  7. “Hôtel de Ville, Limoges × ImmunityBio −8.3% × Alberta separation referendum”, Content, 19 October 2026. JAEV, Lund
    “The text at the top of this page was turned into a fingerprint, the SHA-256 hash below.”

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Published
JAEV Notes, October 2026.
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Text CC BY 4.0. Free to use and quote with credit to JAEV and a link to this page. Images and quotations by others keep their own terms.
All texts as one file: archive.json
Cite
JAEV Notes, “SHA-256 as a source of chance”, jaev.gallery/notes/sha-256-as-random-source/, 2026.
Corrections
Additions and corrections are welcome: info@jaev.gallery
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