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https://github.com/tc39/proposal-csprng

Cryptographically Secure Random Number Generation for ECMAScript
https://github.com/tc39/proposal-csprng

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Cryptographically Secure Random Number Generation for ECMAScript

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# Cryptographically Secure Pseudo-Random Number Generation (CSPRNG) for ECMAScript



This proposes the addition of a user-addressable function that can be used to fill the 

portion of an `ArrayBuffer` associated with a `TypedArray` with cryptographically secure pseudo-random number values.



Portions of this proposal are derived from the [Web Cryptography API](https://w3c.github.io/webcrypto/#Crypto-method-getRandomValues)



## Status



**Stage:** 1  

**Champion:** Ron Buckton (@rbuckton)  



_For detailed status of this proposal see [TODO](#todo), below._  



## Authors



* Ron Buckton (@rbuckton)  



# Motivations



One of the [key issues](https://github.com/tc39/proposal-uuid/issues/37) for https://github.com/tc39/proposal-uuid is the lack

of a "source of truth" for cryptographically secure pseudo-random numbers within the ECMAScript language. While hosts such as 

browsers and NodeJS provide implementations of CSPRNGs (Cryptographically Secure Pseudo-Random Number Generators), the ECMAScript

language itself has no mechanism for supplying a CSPRNG that can be used by proposed APIs such as [UUID](https://github.com/tc39/proposal-uuid).



### Goals



* Provide a single "source of truth" for generating cryptographically secure pseudo-random values within the language.

* Provide a single location for mocking the CSPRNG, vs a method on each `TypedArray` prototype.

* If introducing a new `crypto` global namespace for cryptography-related APIs in ECMA-262, we should ensure that the Web cryptography APIs could be layered on top.



# Prior Art 



* Web Cryptography API: [`crypto.getRandomValues`](https://w3c.github.io/webcrypto/#Crypto-method-getRandomValues)

* NodeJS: [`crypto.randomFillSync`](https://nodejs.org/dist/latest-v13.x/docs/api/crypto.html#crypto_crypto_randomfillsync_buffer_offset_size)



# API



We are still investigating the API surface area for this proposal. The intended API would be a user-addressable function that when called executes the [FillRandomValues](#fillrandomvalues-view) abstract operation, below.



The Stage 0 API proposal exposed this as a static `ArrayBuffer.fillRandom` method, although we are continuing to investigate this space.



# Abstract Operations



## FillRandomValues (view)



When abstract operation FillRandomValues is called with argument _view_, the following steps are taken:



1. Perform ? RequireInternalSlot(_view_, \[\[TypedArrayName]]).

1. Assert: _view_ has the \[\[ViewedArrayBuffer]], \[\[ByteLength]], and \[\[ByteOffset\]\] internal slots.

1. If _view_.\[\[TypedArrayName]] is not one of `"Int8Array"`, `"Uint8Array"`, `"Uint8ClampedArray"`, `"Int16Array"`, `"Uint16Array"`, `"Int32Array"`, `"Uint32Array"`, `"BigInt64Array"`, or `"BigUint64Array"`, throw a **TypeError** exception.

1. Let _buffer_ be _view_.\[\[ViewedArrayBuffer]].

1. If ! IsDetachedBuffer(_buffer_) is **true**, throw a **TypeError** exception.

1. Let _byteLength_ be _view_.\[\[ByteLength]].

1. If _byteLength_ is greater than 65536, throw a **RangeError** exception.

1. Let _byteOffset_ be _view_.\[\[ByteOffset]].

1. Let _byteEndOffset_ be _byteOffset_ + _byteLength_.

1. Overwrite the elements of _buffer_ from index _byteOffset_ (inclusive) through index _byteEndOffset_ (exclusive) with cryptographically secure random values.

1. Return _view_.



> **Note**  

> Implementations should generate cryptographically secure random values using well-established cryptographic pseudo-random number generators seeded with high-quality entropy, such as from an operating-system entropy source (e.g., "/dev/urandom"). This specification provides no lower-bound on the information theoretic entropy present in cryptographically secure random values, but implementations should make a best effort to provide as much entropy as practicable.



> **Note**  

> This interface defines a synchronous method for obtaining cryptographically secure random values. While some devices and implementations may support truly random cryptographic number generators or provide interfaces that block when there is insufficient entropy, implementations are discouraged from using these sources when implementing getRandomValues, both for performance and to avoid depleting the system of entropy. Instead, these sources should be used to seed a cryptographic pseudo-random number generator that can then return suitable values efficiently.



# References



* [Web Cryptography API](https://w3c.github.io/webcrypto/#Crypto-method-getRandomValues)

* [UUID Proposal](https://github.com/tc39/proposal-uuid)



# Prior Discussion



* *Separate proposal for CSPRNG "source of truth"*: https://github.com/tc39/proposal-uuid/issues/37  



# TODO



The following is a high-level list of tasks to progress through each stage of the [TC39 proposal process](https://tc39.es/process-document/):



### Stage 1 Entrance Criteria



* [x] Identified a "[champion][Champion]" who will advance the addition.  

* [x] [Prose][Prose] outlining the problem or need and the general shape of a solution.  

* [x] Illustrative [examples][Examples] of usage.  

* [x] High-level [API][API].  



### Stage 2 Entrance Criteria



* [ ] [Initial specification text][Specification].  

* [ ] [Transpiler support][Transpiler] (_Optional_).  



### Stage 3 Entrance Criteria



* [ ] [Complete specification text][Specification].  

* [ ] Designated reviewers have [signed off][Stage3ReviewerSignOff] on the current spec text.  

* [ ] The ECMAScript editor has [signed off][Stage3EditorSignOff] on the current spec text.  



### Stage 4 Entrance Criteria



* [ ] [Test262](https://github.com/tc39/test262) acceptance tests have been written for mainline usage scenarios and [merged][Test262PullRequest].  

* [ ] Two compatible implementations which pass the acceptance tests: [\[1\]][Implementation1], [\[2\]][Implementation2].  

* [ ] A [pull request][Ecma262PullRequest] has been sent to tc39/ecma262 with the integrated spec text.  

* [ ] The ECMAScript editor has signed off on the [pull request][Ecma262PullRequest].  



[Process]: https://tc39.es/process-document/

[Proposals]: https://github.com/tc39/proposals/

[Grammarkdown]: http://github.com/rbuckton/grammarkdown#readme

[Champion]: #status

[Prose]: #motivations

[Examples]: #examples

[API]: #api

[Specification]: https://tc39.es/proposal-csprng/

[Transpiler]: #todo

[Stage3ReviewerSignOff]: #todo

[Stage3EditorSignOff]: #todo

[Test262PullRequest]: #todo

[Implementation1]: #todo

[Implementation2]: #todo

[Ecma262PullRequest]: #todo