XSalsa20s

XSalsa20s refers to a specific implementation or variant of the Salsa20 stream cipher. Salsa20 itself is a fast, secure stream cipher designed by Daniel J. Bernstein. The "XSalsa20" designation typically indicates an extended nonce version of Salsa20. This extended nonce capability means that XSalsa20 can use a nonce of 192 bits (24 bytes) instead of the standard 64 bits (8 bytes) found in the original Salsa20. This larger nonce size significantly reduces the risk of nonce reuse, which is a critical security consideration for stream ciphers. Using the same nonce with the same key for two different messages can lead to catastrophic security failures, allowing an attacker to recover the keystream and potentially decrypt all messages encrypted with that key and nonce pair. The 192-bit nonce in XSalsa20 provides a much larger space of possible nonces, making accidental reuse highly improbable, even in scenarios where many messages are encrypted. XSalsa20 retains the core cryptographic strength of Salsa20, including its speed and resistance to known attacks. It is often used in cryptographic libraries and protocols where a high degree of security and ease of use are desired.