PHP sodium_crypto_stream_xor() Function: Usage and Examples

In PHP, sodium_crypto_stream_xor() is useful when your application needs a specific operation rather than manually reproducing it. Encrypts or decrypts data by XOR with XSalsa20 keystream. Reusing a nonce and key pair exposes relationships between messages.

Security context: The examples show API usage, not a complete secure messaging protocol. Keep encryption keys secret and use authenticated encryption when integrity is required.

Stream functions work with PHP stream resources, wrappers, contexts or custom filters. Not every wrapper supports every operation.

What Is sodium_crypto_stream_xor() in PHP?

Encrypts or decrypts data by XOR with XSalsa20 keystream. Reusing a nonce and key pair exposes relationships between messages.

Signature:

sodium_crypto_stream_xor(string $message, string $nonce, string $key): string

Parameters:

$message — Bytes to authenticate and encrypt.
$nonce — Unique nonce for the selected algorithm and key; nonce reuse can break confidentiality.
$key — Secret symmetric key or lookup key, depending on the function; never log cryptographic keys.

Return value: string.

Example 1: Basic Usage

This first example shows the method or function in a minimal context. For environment-dependent operations, adapt the required path, stream or connection before running it.

<?php

$key = sodium_crypto_stream_keygen();
$nonce = random_bytes(SODIUM_CRYPTO_STREAM_NONCEBYTES);
$ciphertext = sodium_crypto_stream_xor("Record one", $nonce, $key);
echo sodium_crypto_stream_xor($ciphertext, $nonce, $key);

The important operation is sodium_crypto_stream_xor(). Encrypts or decrypts data by XOR with XSalsa20 keystream.

Example 2: Another Input or Scenario

The next example changes the input or surrounding context to show how the operation behaves in a second situation.

<?php

$key = sodium_crypto_stream_keygen();
$nonce = random_bytes(SODIUM_CRYPTO_STREAM_NONCEBYTES);
$ciphertext = sodium_crypto_stream_xor("Record two", $nonce, $key);
echo sodium_crypto_stream_xor($ciphertext, $nonce, $key);

Compare the inputs and the handling of the return value with the first example. Avoid assuming that filesystem paths, resource states or binary bytes are interchangeable.

Practical Example: Applying the Operation

This example illustrates how the operation fits into a small application workflow. Paths, streams and secrets must be created or provided securely by the calling application.

<?php

$key = sodium_crypto_stream_keygen();
$nonce = random_bytes(SODIUM_CRYPTO_STREAM_NONCEBYTES);
$ciphertext = sodium_crypto_stream_xor("Record three", $nonce, $key);
echo sodium_crypto_stream_xor($ciphertext, $nonce, $key);

Practical note: Encrypts or decrypts data by XOR with XSalsa20 keystream. Reusing a nonce and key pair exposes relationships between messages.

Important Behavior and Edge Cases

Encrypts or decrypts data by XOR with XSalsa20 keystream. Reusing a nonce and key pair exposes relationships between messages.
Check failure values and exceptions; do not assume every environment supports the same stream wrapper, extension or filesystem capability.
When handling paths, streams or external input, validate inputs before using results and release resources after use.

Comparison With Related Functions

Function or Method	Behavior
`sodium_crypto_stream_xor()`	works on raw stream cipher data without built-in authentication.
`sodium_crypto_secretstream_xchacha20poly1305_push()`	authenticates each encrypted chunk.

Common Beginner Mistakes

Mistake	Correct Approach
Assuming `sodium_crypto_stream_xor()` can be used without its required setup	Provide the correct file, stream, state, key or object before calling it; Encrypts or decrypts data by XOR with XSalsa20 keystream.
Reusing a nonce with the same stream key	Generate fresh nonces as the API requires; never reuse a key/nonce pair for independent messages.
Treating encryption as proof that data was not altered	Raw stream ciphers do not authenticate messages; use authenticated encryption for data whose integrity matters.

Key Takeaways

sodium_crypto_stream_xor() encrypts or decrypts data by XOR with XSalsa20 keystream. Reusing a nonce and key pair exposes relationships between messages.
Use appropriate input types and verify results before continuing.
Prefer specialized, safer APIs when the operation concerns untrusted input, encryption or network traffic.

In summary: Encrypts or decrypts data by XOR with XSalsa20 keystream. Reusing a nonce and key pair exposes relationships between messages. Build in error handling and use this function where its specific behavior matches the application requirements.