vcPresentationFormat.js

/**
 * Standards Referenced:
 * JSON Web Encryption (JWE) https://tools.ietf.org/html/rfc7516
 * JSON Object Signing and Encryption (JOSE) https://www.iana.org/assignments/jose/jose.xhtml
 */
const crypto = require('crypto')
const base64url = require('base64url')

// The location of the document within some third party service that will host these documents
const DOCUMENT_URL          = 'https://example.com/docs/VRdqHY1xwB'
const DOCUMENT_ACCESS_TOKEN = 'd2925f29fcd7'

const JWE_ALG               = 'A256KW'
const JWE_ENC               = 'A256CBC-HS512'
const ENCRYPTION_ALGORITHM  = 'aes-256-cbc'
const IV_LENGTH             = 16
const KEY_LENGTH            = 32

/**
 * 
 * @param {Object} jwe JWE JSON Serialization https://tools.ietf.org/html/rfc7516#section-3.2
 * @param {String} key The shared secret to 
 * @returns {Object} 
 *  @param {String} plaintext
 */
const decrypt = ({ jwe, key }) => {
    const ciphertextBuffer = Buffer.from(jwe.ciphertext, 'base64') 
    const keyBuffer = Buffer.from(key, 'base64') 
    const ivBuffer = Buffer.from(jwe.iv, 'base64') 
    // Note pull alg and enc from JWE header and interpret how to decrypt in practise
    const decipher = crypto.createDecipheriv(ENCRYPTION_ALGORITHM, keyBuffer, ivBuffer) 
    const decrypted = decipher.update(ciphertextBuffer) 
    const decryptedBuffer = Buffer.concat([decrypted, decipher.final()]) 
    const plaintext = decryptedBuffer.toString()
    return { plaintext }
}


/**
 * 
 * @param {String} plaintext
 * @returns 
 *  @param {Object} jwe JWE JSON Serialization https://tools.ietf.org/html/rfc7516#section-3.2
 *  @param {String} key The shared secret to decrypt
 */
const encrypt = ({ plaintext }) => {
    const keyBuffer = crypto.randomBytes(KEY_LENGTH) 
    const ivBuffer = crypto.randomBytes(IV_LENGTH) 
    let cipher = crypto.createCipheriv(ENCRYPTION_ALGORITHM, keyBuffer, ivBuffer) 
    let encrypted = cipher.update(plaintext) 
    const encryptedBuffer = Buffer.concat([encrypted, cipher.final()]) 
    const header = {
        alg: JWE_ALG,
        enc: JWE_ENC,
    }
    const protected = base64url(JSON.stringify(header))
    const iv = base64url(ivBuffer)
    const key = base64url(keyBuffer)
    const ciphertext = base64url(encryptedBuffer)
    const jwe = { protected, iv, ciphertext }
    return { jwe, key }
}

const run = async () => {
    const verifiableCredential = {
        '@context':[
            'https://www.w3.org/2018/credentials/v1',
            'https://www.w3.org/2018/credentials/examples/v1'
        ],
        'id':'http://example.gov/credentials/3732',
        'type':[
            'VerifiableCredential',
            'UniversityDegreeCredential'
        ],
        'issuer':'did:key:z6Mkq28Lfc8TwdaujZT8P2vWcs9eDnWKjXyYom6EgDxjCK1j',
        'issuanceDate':'2020-03-10T04:24:12.164Z',
        'credentialSubject':{
            'id':'http://example.com/subject/123',
            'degree':{
            'type':'BachelorDegree',
            'name':'Bachelor of Science and Arts'
            }
        },
        'proof':{
            'type':'Ed25519Signature2018',
            'created':'2020-03-10T04:24:12.164Z',
            'jws':'eyJhbGciOiJFZERTQSIsImI2NCI6ZmFsc2UsImNyaXQiOlsiYjY0Il19..gsjCEscxfFpe7Kith8tmwp7U3UBTjK7DIzPjfyfXXfzYmRH8IMEmcyUCt-mTJHB7tC6-fAgWPN7VNY0AvT2kCA',
            'proofPurpose':'assertionMethod',
            'verificationMethod':'did:key:z6Mkq28Lfc8TwdaujZT8P2vWcs9eDnWKjXyYom6EgDxjCK1j#z6Mkq28Lfc8TwdaujZT8P2vWcs9eDnWKjXyYom6EgDxjCK1j'
        }
    }
    const inputPlaintext = JSON.stringify(verifiableCredential)
    const { jwe, key } = encrypt({ plaintext: inputPlaintext })
    console.log({ jwe })

    const { plaintext } = decrypt({ jwe, key })
    const vc = JSON.parse(plaintext)
    console.log({ vc })

    const urlQuery = new URLSearchParams({ key, access_token: DOCUMENT_ACCESS_TOKEN })
    const queryString = urlQuery.toString()
    const proposedUrl = `${DOCUMENT_URL}?${queryString}`
    console.log({ proposedUrl })
}

run()