Module chacha20

Available on crate feature dep_orion only.

IETF ChaCha20 as specified in the RFC 8439.

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.

nonce: “Counters and LFSRs are both acceptable ways of generating unique nonces, as is encrypting a counter using a block cipher with a 64-bit block size such as DES. Note that it is not acceptable to use a truncation of a counter encrypted with block ciphers with 128-bit or 256-bit blocks, because such a truncation may repeat after a short time.” See RFC for more information.

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 keystream blocks are processed or 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.
• To securely generate a strong key, use SecretKey::generate().

Recommendation:

• It is recommended to use XChaCha20Poly1305 when possible.

Example:

use orion::hazardous::stream::chacha20;

let secret_key = chacha20::SecretKey::generate();

// WARNING: This nonce is only meant for demonstration and should not
// be repeated. Please read the security section.
let nonce = chacha20::Nonce::from([0u8; 12]);
let message = "Data to protect".as_bytes();

// The length of this message is 15.

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

chacha20::encrypt(&secret_key, &nonce, 0, message, &mut dst_out_ct)?;

chacha20::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 ChaCha20 and ChaCha20-Poly1305 use.

SecretKey

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

Constants

CHACHA_KEYSIZE

The key size for ChaCha20.

IETF_CHACHA_NONCESIZE

The nonce size for IETF ChaCha20.

Functions

decrypt

IETF ChaCha20 decryption as specified in the RFC 8439.

encrypt

IETF ChaCha20 encryption as specified in the RFC 8439.