@tanglelabs/resolver-did-key/src/drivers/secp521r1.ts

Fork of Sphereon did:key resolver with BBS+/BLS and EBSI support.

// Brent Shambaugh <brent.shambaugh@gmail.com>. 2021.

import * as u8a from 'uint8arrays'

import * as nist_weierstrauss from 'nist-weierstrauss'
import { base64urlPoint } from 'nist-weierstrauss'
import { KeyToDidDocArgs } from '../types'

/**
 * Constructs the document based on the method key
 */
export function keyToDidDoc({ pubKeyBytes, fingerprint }: KeyToDidDocArgs): any {
  const did = `did:key:${fingerprint}`
  const keyId = `${did}#${fingerprint}`
  const key = pubKeyBytesToXY(pubKeyBytes)
  return {
    id: did,
    verificationMethod: [
      {
        id: keyId,
        type: 'JsonWebKey2020',
        controller: did,
        publicKeyJwk: {
          kty: 'EC',
          crv: 'P-521',
          x: key.xm,
          y: key.ym,
        },
      },
    ],
    authentication: [keyId],
    assertionMethod: [keyId],
    capabilityDelegation: [keyId],
    capabilityInvocation: [keyId],
  }
}

/**
 *
 * @param pubKeyBytes - public key as compressed with 0x02 prefix if even and 0x03 prefix if odd.
 * @returns point x,y with coordinates as multibase encoded base64urls
 *
 * See the the did:key specification: https://w3c-ccg.github.io/did-method-key/#p-521.
 * For compression see: https://tools.ietf.org/id/draft-jivsov-ecc-compact-05.html#rfc.section.3
 * @throws TypeError: input cannot be null or undefined.
 * @throws Error: Unexpected pubKeyBytes
 * @internal
 */
export function pubKeyBytesToXY(pubKeyBytes: Uint8Array): base64urlPoint {
  if (!nist_weierstrauss.nist_weierstrauss_common.testUint8Array(pubKeyBytes)) {
    throw new TypeError('input must be a Uint8Array')
  }
  const publicKeyHex = nist_weierstrauss.nist_weierstrauss_common.pubKeyBytesToHex(pubKeyBytes)

  // compressed p-521 key, SEC format
  // publicKeyHex.length / 2.0 = 67.0 bytes
  if (132 <= publicKeyHex.length && publicKeyHex.length <= 134) {
    if (publicKeyHex.slice(0, 2) == '03' || publicKeyHex.slice(0, 2) == '02') {
      const publicKey = u8a.fromString(publicKeyHex, 'base16')
      const point = nist_weierstrauss.secp521r1.ECPointDecompress(publicKey)
      return nist_weierstrauss.nist_weierstrauss_common.publicKeyIntToXY(point)
    }
  }

  throw new Error('Unexpected pubKeyBytes')
}

export default { keyToDidDoc }