Module xchacha20

Available on crate feature dep_orion only.

XChaCha20 as specified in the draft-irtf-cfrg-xchacha-03.

Parameters:

• secret_key: The secret key.
• nonce: The nonce value.
• initial_counter: The initial counter value. In most cases, this is 0.
• ciphertext: The encrypted data.
• plaintext: The data to be encrypted.
• dst_out: Destination array that will hold the ciphertext/plaintext after encryption/decryption.

dst_out: The output buffer may have a capacity greater than the input. If this is the case, only the first input length amount of bytes in dst_out are modified, while the rest remain untouched.

Errors:

An error will be returned if:

• The length of dst_out is less than plaintext or ciphertext.
• plaintext or ciphertext is empty.
• The initial_counter is high enough to cause a potential overflow.

Even though dst_out is allowed to be of greater length than plaintext, the ciphertext produced by chacha20/xchacha20 will always be of the same length as the plaintext.

Panics:

A panic will occur if:

• More than 2^32-1 * 64 bytes of data are processed.

Security:

• It is critical for security that a given nonce is not re-used with a given key. Should this happen, the security of all data that has been encrypted with that given key is compromised.
• Functions herein do not provide any data integrity. If you need data integrity, which is nearly always the case, you should use an AEAD construction instead. See the aead module for this.
• Only a nonce for XChaCha20 is big enough to be randomly generated using a CSPRNG. Nonce::generate() can be used for this.
• To securely generate a strong key, use SecretKey::generate().

Recommendation:

• It is recommended to use XChaCha20Poly1305 when possible.

Example:

use orion::hazardous::stream::xchacha20;

let secret_key = xchacha20::SecretKey::generate();
let nonce = xchacha20::Nonce::generate();
let message = "Data to protect".as_bytes();

// Length of this message is 15

let mut dst_out_pt = [0u8; 15];
let mut dst_out_ct = [0u8; 15];

xchacha20::encrypt(&secret_key, &nonce, 0, message, &mut dst_out_ct)?;

xchacha20::decrypt(&secret_key, &nonce, 0, &dst_out_ct, &mut dst_out_pt)?;

assert_eq!(dst_out_pt, message);

Structs

Nonce

A type that represents a Nonce that XChaCha20, XChaCha20-Poly1305 use.

SecretKey

A type to represent the SecretKey that Chacha20, XChaCha20, ChaCha20-Poly1305 and XChaCha20-Poly1305 use.

Constants

XCHACHA_NONCESIZE

The nonce size for XChaCha20.

Functions

decrypt

XChaCha20 decryption as specified in the draft RFC.

encrypt

XChaCha20 encryption as specified in the draft RFC.