41 lines
1.1 KiB
JavaScript
41 lines
1.1 KiB
JavaScript
const { createHash } = require('crypto')
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const ecdhComputeSecret = require('./compute_secret')
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const concat = (key, length, value) => {
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const iterations = Math.ceil(length / 32)
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let res
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for (let iter = 1; iter <= iterations; iter++) {
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const buf = Buffer.allocUnsafe(4 + key.length + value.length)
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buf.writeUInt32BE(iter, 0)
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key.copy(buf, 4)
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value.copy(buf, 4 + key.length)
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if (!res) {
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res = createHash('sha256').update(buf).digest()
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} else {
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res = Buffer.concat([res, createHash('sha256').update(buf).digest()])
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}
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}
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return res.slice(0, length)
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}
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const uint32be = (value, buf = Buffer.allocUnsafe(4)) => {
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buf.writeUInt32BE(value)
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return buf
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}
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const lengthAndInput = input => Buffer.concat([uint32be(input.length), input])
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module.exports = (alg, keyLen, privKey, pubKey, { apu = Buffer.alloc(0), apv = Buffer.alloc(0) } = {}, computeSecret = ecdhComputeSecret) => {
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const value = Buffer.concat([
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lengthAndInput(Buffer.from(alg)),
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lengthAndInput(apu),
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lengthAndInput(apv),
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uint32be(keyLen)
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])
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const sharedSecret = computeSecret(privKey, pubKey)
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return concat(sharedSecret, keyLen / 8, value)
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}
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