did-jwt/lib.esm/signers/ES256Signer.js

Library for Signing and Verifying JWTs that use DIDs as issuers and JWEs that use DIDs as recipients

import { bytesToBase64url } from '../util.js';
import { sha256 } from '../Digest.js';
import { p256 } from '@noble/curves/nist.js';
/**
 *  Creates a configured signer function for signing data using the ES256 (secp256r1 + sha256) algorithm.
 *
 *  The signing function itself takes the data as a `Uint8Array` or `string` and returns a `base64Url`-encoded signature
 *
 *  @example
 *  ```typescript
 *  const sign: Signer = ES256Signer(process.env.PRIVATE_KEY)
 *  const signature: string = await sign(data)
 *  ```
 *
 *  @param    {String}    privateKey   a private key as `Uint8Array`
 *  @return   {Function}               a configured signer function `(data: string | Uint8Array): Promise<string>`
 */
export function ES256Signer(privateKey) {
    if (privateKey.length !== 32) {
        throw new Error(`bad_key: Invalid private key format. Expecting 32 bytes, but got ${privateKey.length}`);
    }
    return async (data) => {
        const signature = p256.sign(sha256(data), privateKey, { prehash: false, lowS: false });
        return bytesToBase64url(signature);
    };
}
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