75 lines
2.5 KiB
JavaScript
75 lines
2.5 KiB
JavaScript
const { createCipheriv, createDecipheriv, getCiphers } = require('crypto')
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const uint64be = require('../help/uint64be')
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const timingSafeEqual = require('../help/timing_safe_equal')
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const { KEYOBJECT } = require('../help/consts')
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const { JWEInvalid, JWEDecryptionFailed } = require('../errors')
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const checkInput = function (size, iv, tag) {
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if (iv.length !== 16) {
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throw new JWEInvalid('invalid iv')
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}
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if (arguments.length === 3) {
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if (tag.length !== size / 8) {
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throw new JWEInvalid('invalid tag')
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}
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}
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}
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const encrypt = (size, sign, { [KEYOBJECT]: keyObject }, cleartext, { iv, aad = Buffer.alloc(0) }) => {
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const key = keyObject.export()
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checkInput(size, iv)
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const keySize = size / 8
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const encKey = key.slice(keySize)
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const cipher = createCipheriv(`aes-${size}-cbc`, encKey, iv)
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const ciphertext = Buffer.concat([cipher.update(cleartext), cipher.final()])
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const macData = Buffer.concat([aad, iv, ciphertext, uint64be(aad.length * 8)])
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const macKey = key.slice(0, keySize)
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const tag = sign({ [KEYOBJECT]: macKey }, macData).slice(0, keySize)
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return { ciphertext, tag }
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}
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const decrypt = (size, sign, { [KEYOBJECT]: keyObject }, ciphertext, { iv, tag = Buffer.alloc(0), aad = Buffer.alloc(0) }) => {
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checkInput(size, iv, tag)
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const keySize = size / 8
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const key = keyObject.export()
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const encKey = key.slice(keySize)
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const macKey = key.slice(0, keySize)
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const macData = Buffer.concat([aad, iv, ciphertext, uint64be(aad.length * 8)])
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const expectedTag = sign({ [KEYOBJECT]: macKey }, macData, tag).slice(0, keySize)
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const macCheckPassed = timingSafeEqual(tag, expectedTag)
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if (!macCheckPassed) {
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throw new JWEDecryptionFailed()
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}
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let cleartext
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try {
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const cipher = createDecipheriv(`aes-${size}-cbc`, encKey, iv)
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cleartext = Buffer.concat([cipher.update(ciphertext), cipher.final()])
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} catch (err) {}
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if (!cleartext) {
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throw new JWEDecryptionFailed()
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}
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return cleartext
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}
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module.exports = (JWA, JWK) => {
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['A128CBC-HS256', 'A192CBC-HS384', 'A256CBC-HS512'].forEach((jwaAlg) => {
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const size = parseInt(jwaAlg.substr(1, 3), 10)
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const sign = JWA.sign.get(`HS${size * 2}`)
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if (getCiphers().includes(`aes-${size}-cbc`)) {
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JWA.encrypt.set(jwaAlg, encrypt.bind(undefined, size, sign))
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JWA.decrypt.set(jwaAlg, decrypt.bind(undefined, size, sign))
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JWK.oct.encrypt[jwaAlg] = JWK.oct.decrypt[jwaAlg] = key => (key.use === 'enc' || key.use === undefined) && key.length / 2 === size
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}
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})
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}
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