The Crypto.getRandomValues()
method lets you get cryptographically strong random values. The array given as the parameter is filled with random numbers (random in its cryptographic meaning).
To guarantee enough performance, implementations are not using a truly random number generator, but they are using a pseudo-random number generator seeded with a value with enough entropy. The pseudo-random number generator algorithm (PRNG) may vary across user agents, but is suitable for cryptographic purposes. Implementations are required to use a seed with enough entropy, like a system-level entropy source.
getRandomValues()
is the only member of the Crypto
interface which can be used from an insecure context.
Syntax
typedArray = cryptoObj.getRandomValues(typedArray);
Parameters
typedArray
- An integer-based
TypedArray
, that is anInt8Array
, aUint8Array
, anInt16Array
, aUint16Array
, anInt32Array
, or aUint32Array
. All elements in the array are overwritten with random numbers.
Return value
The same array passed as typedArray
but with its contents replaced with the newly generated random numbers. Note that typedArray
is modified in-place, and no copy is made.
Exceptions
This method can throw an exception under error conditions.
DOMException
(name:QuotaExceededError
)- The requested length exceeds 65,536 bytes.
Usage notes
Don't use getRandomValues()
to generate encryption keys. Instead, use the generateKey()
method. There are a few reasons for this; for example, getRandomValues()
is not guaranteed to be running in a secure context.
There is no minimum degree of entropy mandated by the Web Cryptography specification. User agents are instead urged to provide the best entropy they can when generating random numbers, using a well-defined, efficient pseudorandom number generator built into the user agent itself, but seeded with values taken from an external source of pseudorandom numbers, such as a platform-specific random number function, the Unix /dev/urandom
device, or other source of random or pseudorandom data.
Examples
/* Assuming that window.crypto.getRandomValues is available */ var array = new Uint32Array(10); window.crypto.getRandomValues(array); console.log("Your lucky numbers:"); for (var i = 0; i < array.length; i++) { console.log(array[i]); }
Specification
Specification | Status | Comment |
---|---|---|
Web Cryptography API | Recommendation | Initial definition |
Browser compatibility
Desktop | Mobile | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
getRandomValues() | Chrome Full support 11 | Edge Full support 12 | Firefox Full support 26 | IE Full support 11 | Opera Full support 15 | Safari Full support 6.1 | WebView Android Full support ≤37 | Chrome Android Full support 18 | Firefox Android Full support 26 | Opera Android Full support 14 | Safari iOS Full support 6.1 | Samsung Internet Android Full support 1.0 |
Legend
- Full support
- Full support
See also
- Web Crypto API
Window.crypto
to get aCrypto
object.Math.random
, a non-cryptographic source of random numbers.