To generate a secure random string in PHP, use cryptographically secure functions. 1. Use random_bytes() with bin2hex() for hexadecimal strings, which is secure and simple. 2. For custom character sets, use random_int() within a loop to pick characters from a defined string, ensuring full control over allowed characters. 3. Avoid rand() and mt_rand() for security-sensitive purposes due to predictability and weak randomness.
To generate a random string in PHP, the most reliable way is to use a cryptographically secure method — especially if it's for something like API keys, passwords, or tokens. You don't want predictable randomness when security matters.
Here are a few practical and commonly used approaches:
Use random_bytes() with bin2hex()
This combination is solid because random_bytes() generates cryptographically secure pseudo-random bytes, and bin2hex() converts them into a hexadecimal string.
$bytes = random_bytes(16); // 16 bytes = 32 hex characters echo bin2hex($bytes);
- This will give you a 32-character string containing letters (a–f) and digits.
- If you want more entropy, increase the byte count. For example, 32 bytes would produce a 64-character string.
- The output is not limited to just letters; it includes hexadecimal digits (0–9 and a–f).
If you need only alphanumeric characters, keep reading.
Generate a custom random string from a character set
If you want control over which characters appear in your string (e.g., only uppercase letters and numbers), this approach works well:
function generateRandomString($length = 10) {
$characters = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ';
$charCount = strlen($characters);
$result = '';
for ($i = 0; $i < $length; $i ) {
$result .= $characters[random_int(0, $charCount - 1)];
}
return $result;
}
echo generateRandomString(12); // e.g., "XK9L2B7ZP4QR"- We're using
random_int()here because it's CSPRNG-safe (cryptographically secure). - This lets you define exactly what characters are allowed.
- It’s easy to tweak: just change the
$charactersstring.
You can also include lowercase letters by adding abcdefghijklmnopqrstuvwxyz, or symbols like -!@#.
Bonus tip: Don’t use rand() or mt_rand() for security-sensitive strings
These functions are not suitable for generating secure tokens or passwords:
- They’re predictable.
- Their randomness isn't strong enough for cryptographic purposes.
If someone guesses the seed value, they can reproduce the entire sequence of generated values.
So stick with random_bytes() or random_int() whenever security matters.
That’s basically how you do it in modern PHP without relying on outdated or insecure methods.
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