Install
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
- Integrity Generation
- Integrity Verification
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.
?foometadata 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}))
