| 1 | import { base64ToBytes, bytesToBase64url, decodeBase64url, stringToBytes, toSealed } from '../util.js'
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| 2 | import type { Decrypter, Encrypter, EncryptionResult, EphemeralKeyPair, JWE, ProtectedHeader } from './types.js'
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| 3 |
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| 4 | function validateJWE(jwe: JWE) {
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| 5 | if (!(jwe.protected && jwe.iv && jwe.ciphertext && jwe.tag)) {
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| 6 | throw new Error('bad_jwe: missing properties')
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| 7 | }
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| 8 | if (jwe.recipients) {
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| 9 | jwe.recipients.map((rec) => {
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| 10 | if (!(rec.header && rec.encrypted_key)) {
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| 11 | throw new Error('bad_jwe: malformed recipients')
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| 12 | }
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| 13 | })
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| 14 | }
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| 15 | }
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| 16 |
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| 17 | function encodeJWE({ ciphertext, tag, iv, protectedHeader, recipient }: EncryptionResult, aad?: Uint8Array): JWE {
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| 18 | const jwe: JWE = {
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| 19 | protected: <string>protectedHeader,
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| 20 | iv: bytesToBase64url(iv ?? new Uint8Array(0)),
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| 21 | ciphertext: bytesToBase64url(ciphertext),
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| 22 | tag: bytesToBase64url(tag ?? new Uint8Array(0)),
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| 23 | }
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| 24 | if (aad) jwe.aad = bytesToBase64url(aad)
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| 25 | if (recipient) jwe.recipients = [recipient]
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| 26 | return jwe
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| 27 | }
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| 28 |
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| 29 | export async function createJWE(
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| 30 | cleartext: Uint8Array,
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| 31 | encrypters: Encrypter[],
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| 32 | protectedHeader: ProtectedHeader = {},
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| 33 | aad?: Uint8Array,
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| 34 | useSingleEphemeralKey = false
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| 35 | ): Promise<JWE> {
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| 36 | if (encrypters[0].alg === 'dir') {
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| 37 | if (encrypters.length > 1) throw new Error('not_supported: Can only do "dir" encryption to one key.')
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| 38 | const encryptionResult = await encrypters[0].encrypt(cleartext, protectedHeader, aad)
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| 39 | return encodeJWE(encryptionResult, aad)
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| 40 | } else {
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| 41 | const tmpEnc = encrypters[0].enc
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| 42 | if (!encrypters.reduce((acc, encrypter) => acc && encrypter.enc === tmpEnc, true)) {
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| 43 | throw new Error('invalid_argument: Incompatible encrypters passed')
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| 44 | }
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| 45 | let cek: Uint8Array | undefined
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| 46 | let jwe: JWE | undefined
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| 47 | let epk: EphemeralKeyPair | undefined
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| 48 | if (useSingleEphemeralKey) {
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| 49 | epk = encrypters[0].genEpk?.()
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| 50 | const alg = encrypters[0].alg
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| 51 | protectedHeader = { ...protectedHeader, alg, epk: epk?.publicKeyJWK }
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| 52 | }
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| 53 |
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| 54 | for (const encrypter of encrypters) {
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| 55 | if (!cek) {
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| 56 | const encryptionResult = await encrypter.encrypt(cleartext, protectedHeader, aad, epk)
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| 57 | cek = encryptionResult.cek
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| 58 | jwe = encodeJWE(encryptionResult, aad)
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| 59 | } else {
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| 60 | const recipient = await encrypter.encryptCek?.(cek, epk)
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| 61 | if (recipient) {
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| 62 | jwe?.recipients?.push(recipient)
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| 63 | }
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| 64 | }
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| 65 | }
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| 66 | return <JWE>jwe
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| 67 | }
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| 68 | }
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| 69 |
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| 70 | export async function decryptJWE(jwe: JWE, decrypter: Decrypter): Promise<Uint8Array> {
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| 71 | validateJWE(jwe)
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| 72 | const protHeader = JSON.parse(decodeBase64url(jwe.protected))
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| 73 | if (protHeader.enc !== decrypter.enc)
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| 74 | throw new Error(`not_supported: Decrypter does not supported: '${protHeader.enc}'`)
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| 75 | const sealed = toSealed(jwe.ciphertext, jwe.tag)
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| 76 | const aad = stringToBytes(jwe.aad ? `${jwe.protected}.${jwe.aad}` : jwe.protected)
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| 77 | let cleartext = null
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| 78 | if (protHeader.alg === 'dir' && decrypter.alg === 'dir') {
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| 79 | cleartext = await decrypter.decrypt(sealed, base64ToBytes(jwe.iv), aad)
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| 80 | } else if (!jwe.recipients || jwe.recipients.length === 0) {
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| 81 | throw new Error('bad_jwe: missing recipients')
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| 82 | } else {
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| 83 | for (let i = 0; !cleartext && i < jwe.recipients.length; i++) {
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| 84 | const recipient = jwe.recipients[i]
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| 85 | Object.assign(recipient.header, protHeader)
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| 86 | if (recipient.header.alg === decrypter.alg) {
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| 87 | cleartext = await decrypter.decrypt(sealed, base64ToBytes(jwe.iv), aad, recipient)
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| 88 | }
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| 89 | }
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| 90 | }
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| 91 | if (cleartext === null) throw new Error('failure: Failed to decrypt')
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| 92 | return cleartext
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| 93 | }
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