sodium_crypto_scalarmult_ristretto255 multiplies a Ristretto255 group point by a scalar encoded in the required format.
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_scalarmult_ristretto255 multiplies a Ristretto255 group point by a scalar encoded in the required format.
The sodium extension must be enabled.
Syntax and Return Value
sodium_crypto_scalarmult_ristretto255(string $n, string $p): string| Parameter | Purpose |
|---|---|
| $n (string) | Use the PHP signature above to determine the exact expected input type; validate untrusted inputs before calling. |
| $p (string) | Use the PHP signature above to determine the exact expected input type; validate untrusted inputs before calling. |
The declared return type is shown above. Errors can include false results or exceptions depending on this API: Use valid key material, validate peers, and pass a raw shared secret through an appropriate KDF before using it as an encryption key.
Example 1: Basic Operation
The result is raw group data. Do not use it as a session key without a suitable key-derivation protocol.
<?php
$scalar = sodium_crypto_core_ristretto255_scalar_reduce(random_bytes(64));
$peer = sodium_crypto_scalarmult_ristretto255_base(sodium_crypto_core_ristretto255_scalar_reduce(random_bytes(64)));
$result = sodium_crypto_scalarmult_ristretto255($scalar, $peer);
echo strlen($result);Example 2: A Different Use Case
Check the curve-point output size or its non-secret test fingerprint.
<?php
// Check the alternative case.
$scalar = sodium_crypto_core_ristretto255_scalar_reduce(random_bytes(64));
$peer = sodium_crypto_scalarmult_ristretto255_base(sodium_crypto_core_ristretto255_scalar_reduce(random_bytes(64)));
$result = sodium_crypto_scalarmult_ristretto255($scalar, $peer);
var_dump(strlen($result) === 32);Practical Example: Checking the Result
Check the curve-point output size or its non-secret test fingerprint.
<?php
// Verify the expected behavior before using results.
$scalar = sodium_crypto_core_ristretto255_scalar_reduce(random_bytes(64));
$peer = sodium_crypto_scalarmult_ristretto255_base(sodium_crypto_core_ristretto255_scalar_reduce(random_bytes(64)));
$result = sodium_crypto_scalarmult_ristretto255($scalar, $peer);
echo bin2hex(hash("sha256", $result, true));Important Behavior and Edge Cases
Use valid key material, validate peers, and pass a raw shared secret through an appropriate KDF before using it as an encryption key.
Use valid key material, validate peers, and pass a raw shared secret through an appropriate KDF before using it as an encryption key.
Comparison with Related Functions
| Approach | Key distinction |
|---|---|
| sodium_crypto_scalarmult_ristretto255 | sodium_crypto_scalarmult_ristretto255 multiplies a Ristretto255 group point by a scalar encoded in the required format. |
| Related technique | sodium_crypto_kx provides directional session keys with a clearer application-level protocol. |
Common Beginner Mistakes
| Mistake | Correct approach |
|---|---|
| Confusing this operation with a neighboring cryptographic or security mechanism | sodium_crypto_kx provides directional session keys with a clearer application-level protocol. |
| Ignoring a security prerequisite or failure case | Use valid key material, validate peers, and pass a raw shared secret through an appropriate KDF before using it as an encryption key. |
Key Takeaways
- sodium_crypto_scalarmult_ristretto255 multiplies a Ristretto255 group point by a scalar encoded in the required format.
- Use valid key material, validate peers, and pass a raw shared secret through an appropriate KDF before using it as an encryption key.
- sodium_crypto_kx provides directional session keys with a clearer application-level protocol.
Apply this behavior to a real application only after confirming the required extension, configuration and failure handling on the deployment runtime.