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feat: initial support for X25519 ECDH-ES+A256KW for JWE (#279)
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,150 @@ | ||
| import { randomBytes } from '@stablelib/random' | ||
| import { generateKeyPair, generateKeyPairFromSeed, KeyPair as X25519KeyPair, sharedKey } from '@stablelib/x25519' | ||
| import { Decrypter, Encrypter, EncryptionResult, EphemeralKeyPair, ProtectedHeader, Recipient } from './JWE.js' | ||
| import { concatKDF } from './Digest.js' | ||
| import { base64ToBytes, bytesToBase64url } from './util.js' | ||
| import { genX25519EphemeralKeyPair, xc20pDirDecrypter, xc20pDirEncrypter } from './xc20pEncryption.js' | ||
| import crypto from 'isomorphic-webcrypto' | ||
| import { ECDH } from './ECDH' | ||
|
|
||
| export async function a256KeyWrapper(wrappingKey: Uint8Array) { | ||
| // TODO: check wrapping key size | ||
| const cryptoWrappingKey = await crypto.subtle.importKey( | ||
| 'raw', | ||
| wrappingKey, | ||
| { | ||
| name: 'AES-KW', | ||
| length: 256, | ||
| }, | ||
| false, | ||
| ['wrapKey', 'unwrapKey'] | ||
| ) | ||
|
|
||
| return async (cek: Uint8Array): Promise<Uint8Array> => { | ||
| // create a CryptoKey instance from the cek. The algorithm doesn't matter since we'll be working with raw keys | ||
| const cryptoCek = await crypto.subtle.importKey('raw', cek, { hash: 'SHA-256', name: 'HMAC' }, true, ['sign']) | ||
| return new Uint8Array(await crypto.subtle.wrapKey('raw', cryptoCek, cryptoWrappingKey, 'AES-KW')) | ||
| } | ||
| } | ||
|
|
||
| export async function a256KeyUnwrapper(wrappingKey: Uint8Array) { | ||
| // TODO: check wrapping key size | ||
| const cryptoWrappingKey = await crypto.subtle.importKey( | ||
| 'raw', | ||
| wrappingKey, | ||
| { | ||
| name: 'AES-KW', | ||
| length: 256, | ||
| }, | ||
| false, | ||
| ['wrapKey', 'unwrapKey'] | ||
| ) | ||
|
|
||
| return async (wrappedCek: Uint8Array): Promise<Uint8Array> => { | ||
| const cryptoKeyCek = await crypto.subtle.unwrapKey( | ||
| 'raw', | ||
| wrappedCek, | ||
| cryptoWrappingKey, | ||
| 'AES-KW', | ||
| // algorithm doesn't matter since we'll be exporting as raw | ||
| { hash: 'SHA-256', name: 'HMAC' }, | ||
| true, | ||
| ['sign'] | ||
| ) | ||
|
|
||
| return new Uint8Array(await crypto.subtle.exportKey('raw', cryptoKeyCek)) | ||
| } | ||
| } | ||
|
|
||
| export function x25519EncrypterWithA256KW(publicKey: Uint8Array, kid?: string): Encrypter { | ||
| const alg = 'ECDH-ES+A256KW' | ||
| const keyLen = 256 | ||
| const crv = 'X25519' | ||
|
|
||
| async function encryptCek(cek: Uint8Array, ephemeralKeyPair?: EphemeralKeyPair): Promise<Recipient> { | ||
| const ephemeral: X25519KeyPair = ephemeralKeyPair | ||
| ? generateKeyPairFromSeed(ephemeralKeyPair.secretKey) | ||
| : generateKeyPair() | ||
| const epk = { kty: 'OKP', crv, x: bytesToBase64url(ephemeral.publicKey) } | ||
| const sharedSecret = sharedKey(ephemeral.secretKey, publicKey) | ||
| // Key Encryption Key | ||
| const kek = concatKDF(sharedSecret, keyLen, alg) | ||
| const wrapper = await a256KeyWrapper(kek) | ||
| const res = await wrapper(cek) | ||
| const recipient: Recipient = { | ||
| encrypted_key: bytesToBase64url(res), | ||
| header: {}, | ||
| } | ||
| if (kid) recipient.header.kid = kid | ||
| if (!ephemeralKeyPair) { | ||
| recipient.header.epk = epk | ||
| recipient.header.alg = alg | ||
| } | ||
| return recipient | ||
| } | ||
|
|
||
| async function encrypt( | ||
| cleartext: Uint8Array, | ||
| protectedHeader: ProtectedHeader = {}, | ||
| aad?: Uint8Array, | ||
| ephemeralKeyPair?: EphemeralKeyPair | ||
| ): Promise<EncryptionResult> { | ||
| // we won't want alg to be set to dir from xc20pDirEncrypter | ||
| Object.assign(protectedHeader, { alg: undefined }) | ||
| // Content Encryption Key | ||
| const cek = randomBytes(32) | ||
| const recipient: Recipient = await encryptCek(cek, ephemeralKeyPair) | ||
| if (ephemeralKeyPair) { | ||
| protectedHeader.alg = alg | ||
| protectedHeader.epk = ephemeralKeyPair.publicKey | ||
| delete recipient.header.alg | ||
| delete recipient.header.epk | ||
| } | ||
| return { | ||
| ...(await xc20pDirEncrypter(cek).encrypt(cleartext, protectedHeader, aad)), | ||
| recipient, | ||
| cek, | ||
| } | ||
| } | ||
|
|
||
| return { alg, enc: 'XC20P', encrypt, encryptCek, genEpk: genX25519EphemeralKeyPair } | ||
| } | ||
|
|
||
| export function x25519DecrypterWithA256KW(receiverSecret: Uint8Array | ECDH): Decrypter { | ||
| const alg = 'ECDH-ES+A256KW' | ||
| const keyLen = 256 | ||
| const crv = 'X25519' | ||
|
|
||
| async function decrypt( | ||
| sealed: Uint8Array, | ||
| iv: Uint8Array, | ||
| aad?: Uint8Array, | ||
| recipient?: Recipient | ||
| ): Promise<Uint8Array | null> { | ||
| recipient = <Recipient>recipient | ||
| const header = recipient.header | ||
| if (header.epk?.crv !== crv || typeof header.epk.x == 'undefined') return null | ||
| const publicKey = base64ToBytes(header.epk.x) | ||
| let sharedSecret | ||
| if (receiverSecret instanceof Uint8Array) { | ||
| sharedSecret = sharedKey(receiverSecret, publicKey) | ||
| } else { | ||
| sharedSecret = await receiverSecret(publicKey) | ||
| } | ||
|
|
||
| // Key Encryption Key | ||
| let producerInfo: Uint8Array | undefined = undefined | ||
| let consumerInfo: Uint8Array | undefined = undefined | ||
| if (recipient.header.apu) producerInfo = base64ToBytes(recipient.header.apu) | ||
| if (recipient.header.apv) consumerInfo = base64ToBytes(recipient.header.apv) | ||
| const kek = concatKDF(sharedSecret, keyLen, alg, producerInfo, consumerInfo) | ||
| // Content Encryption Key | ||
| const unwrap = await a256KeyUnwrapper(kek) | ||
| const cek = await unwrap(base64ToBytes(recipient.encrypted_key)) | ||
| if (cek === null) return null | ||
|
|
||
| return xc20pDirDecrypter(cek).decrypt(sealed, iv, aad) | ||
| } | ||
|
|
||
| return { alg, enc: 'XC20P', decrypt } | ||
| } |
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