Phantom rejects an exported Ed25519 key with 'incorrect format': it wants base58 of 64 bytes, private plus public

Symptom: you generate an Ed25519 key with WebCrypto (crypto.subtle.generateKey('Ed25519', ...)) alongside @solana/web3.js v2, base58-encode the private scalar (from JWK d, or the tail of a pkcs8 export), and Phantom refuses the import with "incorrect format".

Cause: what Solana tools call a "secret key" is 64 bytes — the 32-byte Ed25519 private seed followed by the 32-byte public key — base58-encoded (about 87–88 characters). Exporting only the private half gives you 32 bytes, whose base58 form is ~44 characters and looks exactly like a valid Solana address, which is why the output seems plausible and the error seems wrong.

Fix — concatenate before encoding:

const publicKeyBytes = await crypto.subtle.exportKey('raw', keypair.publicKey); const privateKeyBytes = (await crypto.subtle.exportKey('pkcs8', keypair.privateKey)).slice(-32); const secretKeyBytes = new Uint8Array([ ...new Uint8Array(privateKeyBytes), ...new Uint8Array(publicKeyBytes), ]); const encodedSecretKey = getBase58Decoder().decode(secretKeyBytes);

Notes: exportKey('pkcs8') wraps the seed in DER, hence slice(-32) to take the raw seed; the JWK d field is base64url of the same 32 bytes, so it has the same shortfall. In @solana/* v2, getBase58Decoder().decode(bytes) is the byte-array-to-string direction (naming trips people up). The same 64-byte layout is what a id.json keypair file contains as a JSON array, so JSON.stringify(Array.from(secretKeyBytes)) gives a CLI-compatible file. Only do this server-side or in a throwaway context — you are handling raw key material.

Source: adapted from a Stack Exchange answer by steveluscher (question by jonasXchen), https://solana.stackexchange.com/questions/17681/how-to-generate-save-importing-a-keypair-into-phantom-with-solana-web3-js-v2 — CC BY-SA 4.0