diff options
Diffstat (limited to 'test/sequential/test-crypto-timing-safe-equal.js')
-rw-r--r-- | test/sequential/test-crypto-timing-safe-equal.js | 166 |
1 files changed, 166 insertions, 0 deletions
diff --git a/test/sequential/test-crypto-timing-safe-equal.js b/test/sequential/test-crypto-timing-safe-equal.js new file mode 100644 index 0000000000..7b04f15339 --- /dev/null +++ b/test/sequential/test-crypto-timing-safe-equal.js @@ -0,0 +1,166 @@ +'use strict'; +const common = require('../common'); +const assert = require('assert'); + +if (!common.hasCrypto) { + common.skip('missing crypto'); + return; +} + +const crypto = require('crypto'); + +assert.strictEqual( + crypto.timingSafeEqual(Buffer.from('foo'), Buffer.from('foo')), + true, + 'should consider equal strings to be equal' +); + +assert.strictEqual( + crypto.timingSafeEqual(Buffer.from('foo'), Buffer.from('bar')), + false, + 'should consider unequal strings to be unequal' +); + +assert.throws(function() { + crypto.timingSafeEqual(Buffer.from([1, 2, 3]), Buffer.from([1, 2])); +}, 'should throw when given buffers with different lengths'); + +assert.throws(function() { + crypto.timingSafeEqual('not a buffer', Buffer.from([1, 2])); +}, 'should throw if the first argument is not a buffer'); + +assert.throws(function() { + crypto.timingSafeEqual(Buffer.from([1, 2]), 'not a buffer'); +}, 'should throw if the second argument is not a buffer'); + +function getTValue(compareFunc) { + const numTrials = 10000; + const testBufferSize = 10000; + // Perform benchmarks to verify that timingSafeEqual is actually timing-safe. + + const rawEqualBenches = Array(numTrials); + const rawUnequalBenches = Array(numTrials); + + for (let i = 0; i < numTrials; i++) { + + // The `runEqualBenchmark` and `runUnequalBenchmark` functions are + // intentionally redefined on every iteration of this loop, to avoid + // timing inconsistency. + function runEqualBenchmark(compareFunc, bufferA, bufferB) { + const startTime = process.hrtime(); + const result = compareFunc(bufferA, bufferB); + const endTime = process.hrtime(startTime); + + // Ensure that the result of the function call gets used, so it doesn't + // get discarded due to engine optimizations. + assert.strictEqual(result, true); + return endTime[0] * 1e9 + endTime[1]; + } + + // This is almost the same as the runEqualBenchmark function, but it's + // duplicated to avoid timing issues with V8 optimization/inlining. + function runUnequalBenchmark(compareFunc, bufferA, bufferB) { + const startTime = process.hrtime(); + const result = compareFunc(bufferA, bufferB); + const endTime = process.hrtime(startTime); + + assert.strictEqual(result, false); + return endTime[0] * 1e9 + endTime[1]; + } + + if (i % 2) { + const bufferA1 = Buffer.alloc(testBufferSize, 'A'); + const bufferB = Buffer.alloc(testBufferSize, 'B'); + const bufferA2 = Buffer.alloc(testBufferSize, 'A'); + const bufferC = Buffer.alloc(testBufferSize, 'C'); + + // First benchmark: comparing two equal buffers + rawEqualBenches[i] = runEqualBenchmark(compareFunc, bufferA1, bufferA2); + + // Second benchmark: comparing two unequal buffers + rawUnequalBenches[i] = runUnequalBenchmark(compareFunc, bufferB, bufferC); + } else { + // Swap the order of the benchmarks every second iteration, to avoid any + // patterns caused by memory usage. + const bufferB = Buffer.alloc(testBufferSize, 'B'); + const bufferA1 = Buffer.alloc(testBufferSize, 'A'); + const bufferC = Buffer.alloc(testBufferSize, 'C'); + const bufferA2 = Buffer.alloc(testBufferSize, 'A'); + rawUnequalBenches[i] = runUnequalBenchmark(compareFunc, bufferB, bufferC); + rawEqualBenches[i] = runEqualBenchmark(compareFunc, bufferA1, bufferA2); + } + } + + const equalBenches = filterOutliers(rawEqualBenches); + const unequalBenches = filterOutliers(rawUnequalBenches); + + // Use a two-sample t-test to determine whether the timing difference between + // the benchmarks is statistically significant. + // https://wikipedia.org/wiki/Student%27s_t-test#Independent_two-sample_t-test + + const equalMean = mean(equalBenches); + const unequalMean = mean(unequalBenches); + + const equalLen = equalBenches.length; + const unequalLen = unequalBenches.length; + + const combinedStd = combinedStandardDeviation(equalBenches, unequalBenches); + const standardErr = combinedStd * Math.sqrt(1 / equalLen + 1 / unequalLen); + + return (equalMean - unequalMean) / standardErr; +} + +// Returns the mean of an array +function mean(array) { + return array.reduce((sum, val) => sum + val, 0) / array.length; +} + +// Returns the sample standard deviation of an array +function standardDeviation(array) { + const arrMean = mean(array); + const total = array.reduce((sum, val) => sum + Math.pow(val - arrMean, 2), 0); + return Math.sqrt(total / (array.length - 1)); +} + +// Returns the common standard deviation of two arrays +function combinedStandardDeviation(array1, array2) { + const sum1 = Math.pow(standardDeviation(array1), 2) * (array1.length - 1); + const sum2 = Math.pow(standardDeviation(array2), 2) * (array2.length - 1); + return Math.sqrt((sum1 + sum2) / (array1.length + array2.length - 2)); +} + +// Filter large outliers from an array. A 'large outlier' is a value that is at +// least 50 times larger than the mean. This prevents the tests from failing +// due to the standard deviation increase when a function unexpectedly takes +// a very long time to execute. +function filterOutliers(array) { + const arrMean = mean(array); + return array.filter((value) => value / arrMean < 50); +} + +// t_(0.99995, ∞) +// i.e. If a given comparison function is indeed timing-safe, the t-test result +// has a 99.99% chance to be below this threshold. Unfortunately, this means +// that this test will be a bit flakey and will fail 0.01% of the time even if +// crypto.timingSafeEqual is working properly. +// t-table ref: http://www.sjsu.edu/faculty/gerstman/StatPrimer/t-table.pdf +// Note that in reality there are roughly `2 * numTrials - 2` degrees of +// freedom, not ∞. However, assuming `numTrials` is large, this doesn't +// significantly affect the threshold. +const T_THRESHOLD = 3.892; + +const t = getTValue(crypto.timingSafeEqual); +assert( + Math.abs(t) < T_THRESHOLD, + `timingSafeEqual should not leak information from its execution time (t=${t})` +); + +// As a sanity check to make sure the statistical tests are working, run the +// same benchmarks again, this time with an unsafe comparison function. In this +// case the t-value should be above the threshold. +const unsafeCompare = (bufA, bufB) => bufA.equals(bufB); +const t2 = getTValue(unsafeCompare); +assert( + Math.abs(t2) > T_THRESHOLD, + `Buffer#equals should leak information from its execution time (t=${t2})` +); |