ssri

ssri, short for Standard Subresource Integrity, is a Node.js utility for parsing, manipulating, serializing, generating, and verifying Subresource Integrity hashes.

Install

$ npm install --save ssri

Table of Contents

• Example
• Features
• Contributing
• API
  • Parsing & Serializing
    • parse
    • stringify
    • Integrity#concat
    • Integrity#merge
    • Integrity#toString
    • Integrity#toJSON
    • Integrity#match
    • Integrity#pickAlgorithm
    • Integrity#hexDigest
  • Integrity Generation
    • fromHex
    • fromData
    • fromStream
    • create
  • Integrity Verification
    • checkData
    • checkStream
    • integrityStream

Example

const ssri = require('ssri')

const integrity = 'sha512-9KhgCRIx/AmzC8xqYJTZRrnO8OW2Pxyl2DIMZSBOr0oDvtEFyht3xpp71j/r/pAe1DM+JI/A+line3jUBgzQ7A==?foo'

// Parsing and serializing
const parsed = ssri.parse(integrity)
ssri.stringify(parsed) // === integrity (works on non-Integrity objects)
parsed.toString() // === integrity

// Async stream functions
ssri.checkStream(fs.createReadStream('./my-file'), integrity).then(...)
ssri.fromStream(fs.createReadStream('./my-file')).then(sri => {
  sri.toString() === integrity
})
fs.createReadStream('./my-file').pipe(ssri.createCheckerStream(sri))

// Sync data functions
ssri.fromData(fs.readFileSync('./my-file')) // === parsed
ssri.checkData(fs.readFileSync('./my-file'), integrity) // => 'sha512'

Features

• Parses and stringifies SRI strings.
• Generates SRI strings from raw data or Streams.
• Strict standard compliance.
• ?foo metadata option support.
• Multiple entries for the same algorithm.
• Object-based integrity hash manipulation.
• Small footprint: no dependencies, concise implementation.
• Full test coverage.
• Customizable algorithm picker.

Contributing

The ssri team enthusiastically welcomes contributions and project participation! There's a bunch of things you can do if you want to contribute! The Contributor Guide has all the information you need for everything from reporting bugs to contributing entire new features. Please don't hesitate to jump in if you'd like to, or even ask us questions if something isn't clear.

API

> ssri.parse(sri, [opts]) -> Integrity

Parses sri into an Integrity data structure. sri can be an integrity string, an Hash-like with digest and algorithm fields and an optional options field, or an Integrity-like object. The resulting object will be an Integrity instance that has this shape:

{
  'sha1': [{algorithm: 'sha1', digest: 'deadbeef', options: []}],
  'sha512': [
    {algorithm: 'sha512', digest: 'c0ffee', options: []},
    {algorithm: 'sha512', digest: 'bad1dea', options: ['foo']}
  ],
}

If opts.single is truthy, a single Hash object will be returned. That is, a single object that looks like {algorithm, digest, options}, as opposed to a larger object with multiple of these.

If opts.strict is truthy, the resulting object will be filtered such that it strictly follows the Subresource Integrity spec, throwing away any entries with any invalid components. This also means a restricted set of algorithms will be used -- the spec limits them to sha256, sha384, and sha512.

Strict mode is recommended if the integrity strings are intended for use in browsers, or in other situations where strict adherence to the spec is needed.

Example

ssri.parse('sha512-9KhgCRIx/AmzC8xqYJTZRrnO8OW2Pxyl2DIMZSBOr0oDvtEFyht3xpp71j/r/pAe1DM+JI/A+line3jUBgzQ7A==?foo') // -> Integrity object

> ssri.stringify(sri, [opts]) -> String

This function is identical to Integrity#toString(), except it can be used on any object that parse can handle -- that is, a string, an Hash-like, or an Integrity-like.

The opts.sep option defines the string to use when joining multiple entries together. To be spec-compliant, this must be whitespace. The default is a single space (' ').

If opts.strict is true, the integrity string will be created using strict parsing rules. See ssri.parse.

Example

// Useful for cleaning up input SRI strings:
ssri.stringify('\n\rsha512-foo\n\t\tsha384-bar')
// -> 'sha512-foo sha384-bar'

// Hash-like: only a single entry.
ssri.stringify({
  algorithm: 'sha512',
  digest:'9KhgCRIx/AmzC8xqYJTZRrnO8OW2Pxyl2DIMZSBOr0oDvtEFyht3xpp71j/r/pAe1DM+JI/A+line3jUBgzQ7A==',
  options: ['foo']
})
// ->
// 'sha512-9KhgCRIx/AmzC8xqYJTZRrnO8OW2Pxyl2DIMZSBOr0oDvtEFyht3xpp71j/r/pAe1DM+JI/A+line3jUBgzQ7A==?foo'

// Integrity-like: full multi-entry syntax. Similar to output of `ssri.parse`
ssri.stringify({
  'sha512': [
    {
      algorithm: 'sha512',
      digest:'9KhgCRIx/AmzC8xqYJTZRrnO8OW2Pxyl2DIMZSBOr0oDvtEFyht3xpp71j/r/pAe1DM+JI/A+line3jUBgzQ7A==',
      options: ['foo']
    }
  ]
})
// ->
// 'sha512-9KhgCRIx/AmzC8xqYJTZRrnO8OW2Pxyl2DIMZSBOr0oDvtEFyht3xpp71j/r/pAe1DM+JI/A+line3jUBgzQ7A==?foo'

> Integrity#concat(otherIntegrity, [opts]) -> Integrity

Concatenates an Integrity object with another IntegrityLike, or an integrity string.

This is functionally equivalent to concatenating the string format of both integrity arguments, and calling ssri.parse on the new string.

If opts.strict is true, the new Integrity will be created using strict parsing rules. See ssri.parse.

Example

// This will combine the integrity checks for two different versions of
// your index.js file so you can use a single integrity string and serve
// either of these to clients, from a single `<script>` tag.
const desktopIntegrity = ssri.fromData(fs.readFileSync('./index.desktop.js'))
const mobileIntegrity = ssri.fromData(fs.readFileSync('./index.mobile.js'))

// Note that browsers (and ssri) will succeed as long as ONE of the entries
// for the *prioritized* algorithm succeeds. That is, in order for this fallback
// to work, both desktop and mobile *must* use the same `algorithm` values.
desktopIntegrity.concat(mobileIntegrity)

> Integrity#merge(otherIntegrity, [opts])

Safely merges another IntegrityLike or integrity string into an Integrity object.

If the other integrity value has any algorithms in common with the current object, then the hash digests must match, or an error is thrown.

Any new hashes will be added to the current object's set.

This is useful when an integrity value may be upgraded with a stronger algorithm, you wish to prevent accidentally suppressing integrity errors by overwriting the expected integrity value.

Example

const data = fs.readFileSync('data.txt')

// integrity.txt contains 'sha1-X1UT+IIv2+UUWvM7ZNjZcNz5XG4='
// because we were young, and didn't realize sha1 would not last
const expectedIntegrity = ssri.parse(fs.readFileSync('integrity.txt', 'utf8'))
const match = ssri.checkData(data, expectedIntegrity, {
  algorithms: ['sha512', 'sha1']
})
if (!match) {
  throw new Error('data corrupted or something!')
}

// get a stronger algo!
if (match && match.algorithm !== 'sha512') {
  const updatedIntegrity = ssri.fromData(data, { algorithms: ['sha512'] })
  expectedIntegrity.merge(updatedIntegrity)
  fs.writeFileSync('integrity.txt', expectedIntegrity.toString())
  // file now contains
  // 'sha1-X1UT+IIv2+UUWvM7ZNjZcNz5XG4= sha512-yzd8ELD1piyANiWnmdnpCL5F52f10UfUdEkHywVZeqTt0ymgrxR63Qz0GB7TKPoeeZQmWCaz7T1+9vBnypkYWg=='
}

> Integrity#toString([opts]) -> String

Returns the string representation of an Integrity object. All hash entries will be concatenated in the string by opts.sep, which defaults to ' '.

If you want to serialize an object that didn't come from an ssri function, use ssri.stringify().

If opts.strict is true, the integrity string will be created using strict parsing rules. See ssri.parse.

Example

const integrity = 'sha512-9KhgCRIx/AmzC8xqYJTZRrnO8OW2Pxyl2DIMZSBOr0oDvtEFyht3xpp71j/r/pAe1DM+JI/A+line3jUBgzQ7A==?foo'

ssri.parse(integrity).toString() === integrity

> Integrity#toJSON() -> String

Returns the string representation of an Integrity object. All hash entries will be concatenated in the string by ' '.

This is a convenience method so you can pass an Integrity object directly to JSON.stringify. For more info check out toJSON() behavior on mdn.

Example

const integrity = '"sha512-9KhgCRIx/AmzC8xqYJTZRrnO8OW2Pxyl2DIMZSBOr0oDvtEFyht3xpp71j/r/pAe1DM+JI/A+line3jUBgzQ7A==?foo"'

JSON.stringify(ssri.parse(integrity)) === integrity

> Integrity#match(sri, [opts]) -> Hash | false

Returns the matching (truthy) hash if Integrity matches the argument passed as sri, which can be anything that parse will accept. opts will be passed through to parse and pickAlgorithm().

Example

const integrity = 'sha512-9KhgCRIx/AmzC8xqYJTZRrnO8OW2Pxyl2DIMZSBOr0oDvtEFyht3xpp71j/r/pAe1DM+JI/A+line3jUBgzQ7A=='

ssri.parse(integrity).match(integrity)
// Hash {
//   digest: '9KhgCRIx/AmzC8xqYJTZRrnO8OW2Pxyl2DIMZSBOr0oDvtEFyht3xpp71j/r/pAe1DM+JI/A+line3jUBgzQ7A=='
//   algorithm: 'sha512'
// }

ssri.parse(integrity).match('sha1-deadbeef')
// false

> Integrity#pickAlgorithm([opts]) -> String

Returns the "best" algorithm from those available in the integrity object.

If opts.pickAlgorithm is provided, it will be passed two algorithms as arguments. ssri will prioritize whichever of the two algorithms is returned by this function. Note that the function may be called multiple times, and it must return one of the two algorithms provided. By default, ssri will make a best-effort to pick the strongest/most reliable of the given algorithms. It may intentionally deprioritize algorithms with known vulnerabilities.

Example

ssri.parse('sha1-WEakDigEST sha512-yzd8ELD1piyANiWnmdnpCL5F52f10UfUdEkHywVZeqTt0ymgrxR63Qz0GB7TKPoeeZQmWCaz7T1').pickAlgorithm() // sha512

> Integrity#hexDigest() -> String

Integrity is assumed to be either a single-hash Integrity instance, or a Hash instance. Returns its digest, converted to a hex representation of the base64 data.

Example

ssri.parse('sha1-deadbeef').hexDigest() // '75e69d6de79f'

> ssri.fromHex(hexDigest, algorithm, [opts]) -> Integrity

Creates an Integrity object with a single entry, based on a hex-formatted hash. This is a utility function to help convert existing shasums to the Integrity format, and is roughly equivalent to something like:

algorithm + '-' + Buffer.from(hexDigest, 'hex').toString('base64')

opts.options may optionally be passed in: it must be an array of option strings that will be added to all generated integrity hashes generated by fromData. This is a loosely-specified feature of SRIs, and currently has no specified semantics besides being ?-separated. Use at your own risk, and probably avoid if your integrity strings are meant to be used with browsers.

If opts.strict is true, the integrity object will be created using strict parsing rules. See ssri.parse.

If opts.single is true, a single Hash object will be returned.

Example

ssri.fromHex('75e69d6de79f', 'sha1').toString() // 'sha1-deadbeef'

> ssri.fromData(data, [opts]) -> Integrity

Creates an Integrity object from either string or Buffer data, calculating all the requested hashes and adding any specified options to the object.

opts.algorithms determines which algorithms to generate hashes for. All results will be included in a single Integrity object. The default value for opts.algorithms is ['sha512']. All algorithm strings must be hashes listed in crypto.getHashes() for the host Node.js platform.

opts.options may optionally be passed in: it must be an array of option strings that will be added to all generated integrity hashes generated by fromData. This is a loosely-specified feature of SRIs, and currently has no specified semantics besides being ?-separated. Use at your own risk, and probably avoid if your integrity strings are meant to be used with browsers.

If opts.strict is true, the integrity object will be created using strict parsing rules. See ssri.parse.

Example

const integrityObj = ssri.fromData('foobarbaz', {
  algorithms: ['sha256', 'sha384', 'sha512']
})
integrity.toString('\n')
// ->
// sha256-l981iLWj8kurw4UbNy8Lpxqdzd7UOxS50Glhv8FwfZ0=
// sha384-irnCxQ0CfQhYGlVAUdwTPC9bF3+YWLxlaDGM4xbYminxpbXEq+D+2GCEBTxcjES9
// sha512-yzd8ELD1piyANiWnmdnpCL5F52f10UfUdEkHywVZeqTt0ymgrxR63Qz0GB7TKPoeeZQmWCaz7T1+9vBnypkYWg==

> ssri.fromStream(stream, [opts]) -> Promise<Integrity>

Returns a Promise of an Integrity object calculated by reading data from a given stream.

It accepts both opts.algorithms and opts.options, which are documented as part of ssri.fromData.

Additionally, opts.Promise may be passed in to inject a Promise library of choice. By default, ssri will use Node's built-in Promises.

If opts.strict is true, the integrity object will be created using strict parsing rules. See ssri.parse.

Example

ssri.fromStream(fs.createReadStream('index.js'), {
  algorithms: ['sha1', 'sha512']
}).then(integrity => {
  return ssri.checkStream(fs.createReadStream('index.js'), integrity)
}) // succeeds

> ssri.create([opts]) -> <Hash>

Returns a Hash object with update(<Buffer or string>[,enc]) and digest() methods.

The Hash object provides the same methods as crypto class Hash. digest() accepts no arguments and returns an Integrity object calculated by reading data from calls to update.

It accepts both opts.algorithms and opts.options, which are documented as part of ssri.fromData.

If opts.strict is true, the integrity object will be created using strict parsing rules. See ssri.parse.

Example

const integrity = ssri.create().update('foobarbaz').digest()
integrity.toString()
// ->
// sha512-yzd8ELD1piyANiWnmdnpCL5F52f10UfUdEkHywVZeqTt0ymgrxR63Qz0GB7TKPoeeZQmWCaz7T1+9vBnypkYWg==

> ssri.checkData(data, sri, [opts]) -> Hash|false

Verifies data integrity against an sri argument. data may be either a String or a Buffer, and sri can be any subresource integrity representation that ssri.parse can handle.

If verification succeeds, checkData will return the name of the algorithm that was used for verification (a truthy value). Otherwise, it will return false.

If opts.pickAlgorithm is provided, it will be used by Integrity#pickAlgorithm when deciding which of the available digests to match against.

If opts.error is true, and verification fails, checkData will throw either an EBADSIZE or an EINTEGRITY error, instead of just returning false.

Example

const data = fs.readFileSync('index.js')
ssri.checkData(data, ssri.fromData(data)) // -> 'sha512'
ssri.checkData(data, 'sha256-l981iLWj8kurw4UbNy8Lpxqdzd7UOxS50Glhv8FwfZ0')
ssri.checkData(data, 'sha1-BaDDigEST') // -> false
ssri.checkData(data, 'sha1-BaDDigEST', {error: true}) // -> Error! EINTEGRITY

> ssri.checkStream(stream, sri, [opts]) -> Promise<Hash>

Verifies the contents of stream against an sri argument. stream will be consumed in its entirety by this process. sri can be any subresource integrity representation that ssri.parse can handle.

checkStream will return a Promise that either resolves to the Hash that succeeded verification, or, if the verification fails or an error happens with stream, the Promise will be rejected.

If the Promise is rejected because verification failed, the returned error will have err.code as EINTEGRITY.

If opts.size is given, it will be matched against the stream size. An error with err.code EBADSIZE will be returned by a rejection if the expected size and actual size fail to match.

If opts.pickAlgorithm is provided, it will be used by Integrity#pickAlgorithm when deciding which of the available digests to match against.

Example

const integrity = ssri.fromData(fs.readFileSync('index.js'))

ssri.checkStream(
  fs.createReadStream('index.js'),
  integrity
)
// ->
// Promise<{
//   algorithm: 'sha512',
//   digest: 'sha512-yzd8ELD1piyANiWnmdnpCL5F52f10UfUdEkHywVZeqTt0ymgrxR63Qz0GB7TKPoeeZQmWCaz7T1'
// }>

ssri.checkStream(
  fs.createReadStream('index.js'),
  'sha256-l981iLWj8kurw4UbNy8Lpxqdzd7UOxS50Glhv8FwfZ0'
) // -> Promise<Hash>

ssri.checkStream(
  fs.createReadStream('index.js'),
  'sha1-BaDDigEST'
) // -> Promise<Error<{code: 'EINTEGRITY'}>>

> integrityStream([opts]) -> IntegrityStream

Returns a Transform stream that data can be piped through in order to generate and optionally check data integrity for piped data. When the stream completes successfully, it emits size and integrity events, containing the total number of bytes processed and a calculated Integrity instance based on stream data, respectively.

If opts.algorithms is passed in, the listed algorithms will be calculated when generating the final Integrity instance. The default is ['sha512'].

If opts.single is passed in, a single Hash instance will be returned.

If opts.integrity is passed in, it should be an integrity value understood by parse that the stream will check the data against. If verification succeeds, the integrity stream will emit a verified event whose value is a single Hash object that is the one that succeeded verification. If verification fails, the stream will error with an EINTEGRITY error code.

If opts.size is given, it will be matched against the stream size. An error with err.code EBADSIZE will be emitted by the stream if the expected size and actual size fail to match.

If opts.pickAlgorithm is provided, it will be passed two algorithms as arguments. ssri will prioritize whichever of the two algorithms is returned by this function. Note that the function may be called multiple times, and it must return one of the two algorithms provided. By default, ssri will make a best-effort to pick the strongest/most reliable of the given algorithms. It may intentionally deprioritize algorithms with known vulnerabilities.

Example

const integrity = ssri.fromData(fs.readFileSync('index.js'))
fs.createReadStream('index.js')
.pipe(ssri.integrityStream({integrity}))