message: Implement Add `signECDSA` and `verifyECDSA` functions into `encryption.js`
  These functions follow the implementation for ECDSA set out by the 'elliptic' library here:
diff: import { ec as EllipticCurve } from 'elliptic'
  import crypto from 'crypto'
  +import { getPublicKeyFromPrivate } from './keys'
  const ecurve = new EllipticCurve('secp256k1')
  @@ -130,3 +131,26 @@ export function decryptECIES(privateKey: string, cipherObject: string) {
  return plainText
  }
  }
  +
  +export function signECDSA(privateKey: string, content: string | Buffer) {
  + const contentBuffer = Buffer.from(content)
  + const ecPrivate = ecurve.keyFromPrivate(privateKey, 'hex')
  + const publicKey = getPublicKeyFromPrivate(privateKey)
  + const contentHash = hmacSha256(publicKey, contentBuffer)
  + const signature = ecPrivate.sign(contentHash)
  + const signatureString = signature.toDER('hex')
  +
  + return {
  + content,
  + signature: signatureString,
  + publicKey
  + }
  +}
  +
  +export function verifyECDSA(signatureObject: Object) {
  + const { content, signature, publicKey } = signatureObject
  + const ecPublic = ecurve.keyFromPublic(publicKey, 'hex')
  + const contentHash = hmacSha256(publicKey, content)
  +
  + return ecPublic.verify(contentHash, signature)
  +}
  