Dart
Secure random
Learn secure random with Random.secure.
Random.secure
Random.secure is Dart's cryptographically secure random number generator. It lives in the dart:math library. Unlike the regular Random it is unpredictable; it is used for passwords, tokens and session IDs.
Example: import 'dart:math'; final r = Random.secure(); final token = List<int>.generate(32, (_) => r.nextInt(256));. This produces a 32-byte random token. Each byte takes a random value from 0 to 255. You can base64-encode this token and use it as a bearer token. Random() is predictable; it is not suitable for security.
Token generation
To produce a secure token you use Random.secure. The typical pattern is List<int>.generate(length, (_) => r.nextInt(256)). This produces a list where each byte is a random value from 0 to 255. You base64-encode the list to get a string token.
Example: a 32-byte token becomes a 44-character base64 string. This can be used as a session ID, API key or reset token. The key point is to always use Random.secure() instead of Random(); otherwise the token is predictable and security is compromised.
Exercise A token generation function
Add import 'dart:math';. Define generateToken with final r = Random.secure(); and return List<int>.generate(32, (_) => r.nextInt(256)); inside. In main add print('Random.secure: cryptographic random') and print('Token size: 32 bytes').
Show example solution
import 'dart:math';
List<int> generateToken() {
final r = Random.secure();
return List<int>.generate(32, (_) => r.nextInt(256));
}
void main() {
print('Random.secure: cryptographic random');
print('Token size: 32 bytes');
}
Test yourself
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What does Random.secure provide?
- Predictable numbers
- Cryptographically secure random
- Fixed numbers
- Same number
Show answer
Cryptographically secure random — Random.secure provides cryptographically secure random.
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Match the Random.secure parts
- Random.secure
- Secure random
- dart:math
- Library
- nextInt
- Integer
- nextDouble
- Decimal
-
The Random.secure call
final r = ____();
Show answer
final r = Random.secure();
Next lesson: Password hashing
