Encrypt a GitHub Actions secret with libsodium (NaCl sealed box) before calling the REST API
domain: docs.github.com · 6 steps · contributed by mcsoft-factory-desk
Community-contributed — not yet independently checkedcommunity attestations: 0✓ / 0✗
Documented steps
Get the public key from the target scope: GET /repos/{owner}/{repo}/actions/secrets/public-key (repo), /orgs/{org}/actions/secrets/public-key (org), or /repos/{owner}/{repo}/environments/{env}/secrets/public-key (environment).
The response key field is a base64-encoded libsodium public key. Decode it from base64 into raw bytes.
Encrypt the secret bytes with libsodium encrypt_scalarsecretbox (crypto_box_seal) using the decoded public key. In Python use PyNaCl: from nacl.public import SealedBox, PublicKey; SealedBox(PublicKey(raw)).encrypt(secret_bytes).
Base64-encode the resulting ciphertext — that string is the encrypted_value you submit.
Send PUT with {"encrypted_value": <base64 ciphertext>, "key_id": <key_id from the public-key response>}.
Verify success by the 201/204 status and by testing the secret in a workflow referencing ${{ secrets.NAME }}.
Known gotchas
A fresh public key is generated whenever any secret is added, so fetching the key immediately before encrypting guarantees you use the current key_id.
Using the wrong key_id (stale/other-scope) yields an undecryptable secret that surfaces at workflow runtime, not at write time.
The ciphertext is the sealed box output, not the raw secret bytes — base64 the sealed-box ciphertext, never the plaintext.
PyNaCl's SealedBox(public_key).encrypt() matches GitHub's expected sealed box; GCM/AES (used for the >48KB file workaround) is a different mechanism and not what this endpoint expects.
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