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

<a name="parse"></a> > 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

<a name="stringify"></a> > 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'

<a name="integrity-concat"></a> > 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)

<a name="integrity-merge"></a> > 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=='
}

<a name="integrity-to-string"></a> > 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

<a name="integrity-to-json"></a> > 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

<a name="integrity-match"></a> `> Integrity#match(s