sodium_crypto_kdf_derive_from_key derives a unique subkey from a master key, context and subkey ID.
The examples explain the data format, expected results and the difference between this API and nearby cryptographic operations.
What It Does
The operation is intended for: sodium_crypto_kdf_derive_from_key derives a unique subkey from a master key, context and subkey ID.
The sodium extension must be enabled.
Syntax and Return Value
sodium_crypto_kdf_derive_from_key(int $subkey_length, int $subkey_id, string $context, string $key): string| Parameter | Purpose |
|---|---|
| $subkey_length (int) | Use the PHP signature above to determine the exact expected input type; validate untrusted inputs before calling. |
| $subkey_id (int) | An integer ID for deriving distinct subkeys. |
| $context (string) | A fixed domain-separation label; do not mix keys from unrelated purposes. |
| $key (string) | Raw key bytes in the required algorithm-specific length; protect them from disclosure. |
The declared return type is shown above. Errors can include false results or exceptions depending on this API: Use a unique non-secret context and distinct identifiers for domains; protect the master key.
Example 1: Basic Operation
Context strings must be exactly eight bytes; use distinct subkey IDs for independent uses.
<?php
$master = sodium_crypto_kdf_keygen();
$derived = sodium_crypto_kdf_derive_from_key(32, 1, "EXAMPLES", $master);
echo strlen($derived);Example 2: A Different Use Case
Context strings must be exactly eight bytes; use distinct subkey IDs for independent uses.
<?php
// Check the alternative case.
$master = sodium_crypto_kdf_keygen();
$derived = sodium_crypto_kdf_derive_from_key(32, 2, "EXAMPLES", $master);
echo strlen($derived);Practical Example: Checking the Result
Context strings must be exactly eight bytes; use distinct subkey IDs for independent uses.
<?php
// Verify the expected behavior before using results.
$master = sodium_crypto_kdf_keygen();
$derived = sodium_crypto_kdf_derive_from_key(32, 3, "EXAMPLES", $master);
echo strlen($derived);Important Behavior and Edge Cases
Use a unique non-secret context and distinct identifiers for domains; protect the master key.
Use a unique non-secret context and distinct identifiers for domains; protect the master key.
Comparison with Related Functions
| Approach | Key distinction |
|---|---|
| sodium_crypto_kdf_derive_from_key | sodium_crypto_kdf_derive_from_key derives a unique subkey from a master key, context and subkey ID. |
| Related technique | sodium_crypto_pwhash derives a key from a human password instead of a strong master key. |
Common Beginner Mistakes
| Mistake | Correct approach |
|---|---|
| Confusing this operation with a neighboring cryptographic or security mechanism | sodium_crypto_pwhash derives a key from a human password instead of a strong master key. |
| Ignoring a security prerequisite or failure case | Use a unique non-secret context and distinct identifiers for domains; protect the master key. |
Key Takeaways
- sodium_crypto_kdf_derive_from_key derives a unique subkey from a master key, context and subkey ID.
- Use a unique non-secret context and distinct identifiers for domains; protect the master key.
- sodium_crypto_pwhash derives a key from a human password instead of a strong master key.
Apply this behavior to a real application only after confirming the required extension, configuration and failure handling on the deployment runtime.