Use constant size generic parameter for random bytes generation

All uses of `get_random()` were in the form of:

  `&get_random(vec![0u8; SIZE])`

with `SIZE` being a constant.

Building a `Vec` is unnecessary for two reasons. First, it uses a
very short-lived dynamic memory allocation. Second, a `Vec` is a
resizable object, which is useless in those context when random
data have a fixed size and will only be read.

`get_random_bytes()` takes a constant as a generic parameter and
returns an array with the requested number of random bytes.

Stack safety analysis: the random bytes will be allocated on the
caller stack for a very short time (until the encoding function has
been called on the data). In some cases, the random bytes take
less room than the `Vec` did (a `Vec` is 24 bytes on a 64 bit
computer). The maximum used size is 180 bytes, which makes it
for 0.008% of the default stack size for a Rust thread (2MiB),
so this is a non-issue.

Also, most of the uses of those random bytes are to encode them
using an `Encoding`. The function `crypto::encode_random_bytes()`
generates random bytes and encode them with the provided
`Encoding`, leading to code deduplication.

`generate_id()` has also been converted to use a constant generic
parameter as well since the length of the requested String is always
a constant.
This commit is contained in:
Samuel Tardieu 2022-11-11 10:55:04 +01:00
parent 7a7673103f
commit d0baa23f9a
5 changed files with 19 additions and 12 deletions

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@ -34,7 +34,7 @@ async fn generate_authenticator(data: JsonUpcase<PasswordData>, headers: Headers
let (enabled, key) = match twofactor { let (enabled, key) = match twofactor {
Some(tf) => (true, tf.data), Some(tf) => (true, tf.data),
_ => (false, BASE32.encode(&crypto::get_random(vec![0u8; 20]))), _ => (false, crypto::encode_random_bytes::<20>(BASE32)),
}; };
Ok(Json(json!({ Ok(Json(json!({

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@ -105,7 +105,7 @@ async fn recover(data: JsonUpcase<RecoverTwoFactor>, mut conn: DbConn) -> JsonRe
async fn _generate_recover_code(user: &mut User, conn: &mut DbConn) { async fn _generate_recover_code(user: &mut User, conn: &mut DbConn) {
if user.totp_recover.is_none() { if user.totp_recover.is_none() {
let totp_recover = BASE32.encode(&crypto::get_random(vec![0u8; 20])); let totp_recover = crypto::encode_random_bytes::<20>(BASE32);
user.totp_recover = Some(totp_recover); user.totp_recover = Some(totp_recover);
user.save(conn).await.ok(); user.save(conn).await.ok();
} }

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@ -56,7 +56,7 @@ fn negotiate(_headers: Headers) -> Json<JsonValue> {
use crate::crypto; use crate::crypto;
use data_encoding::BASE64URL; use data_encoding::BASE64URL;
let conn_id = BASE64URL.encode(&crypto::get_random(vec![0u8; 16])); let conn_id = crypto::encode_random_bytes::<16>(BASE64URL);
let mut available_transports: Vec<JsonValue> = Vec::new(); let mut available_transports: Vec<JsonValue> = Vec::new();
if CONFIG.websocket_enabled() { if CONFIG.websocket_enabled() {

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@ -3,7 +3,7 @@
// //
use std::num::NonZeroU32; use std::num::NonZeroU32;
use data_encoding::HEXLOWER; use data_encoding::{Encoding, HEXLOWER};
use ring::{digest, hmac, pbkdf2}; use ring::{digest, hmac, pbkdf2};
static DIGEST_ALG: pbkdf2::Algorithm = pbkdf2::PBKDF2_HMAC_SHA256; static DIGEST_ALG: pbkdf2::Algorithm = pbkdf2::PBKDF2_HMAC_SHA256;
@ -38,17 +38,24 @@ pub fn hmac_sign(key: &str, data: &str) -> String {
// //
pub fn get_random_64() -> Vec<u8> { pub fn get_random_64() -> Vec<u8> {
get_random(vec![0u8; 64]) get_random_bytes::<64>().to_vec()
} }
pub fn get_random(mut array: Vec<u8>) -> Vec<u8> { /// Return an array holding `N` random bytes.
pub fn get_random_bytes<const N: usize>() -> [u8; N] {
use ring::rand::{SecureRandom, SystemRandom}; use ring::rand::{SecureRandom, SystemRandom};
let mut array = [0; N];
SystemRandom::new().fill(&mut array).expect("Error generating random values"); SystemRandom::new().fill(&mut array).expect("Error generating random values");
array array
} }
/// Encode random bytes using the provided function.
pub fn encode_random_bytes<const N: usize>(e: Encoding) -> String {
e.encode(&get_random_bytes::<N>())
}
/// Generates a random string over a specified alphabet. /// Generates a random string over a specified alphabet.
pub fn get_random_string(alphabet: &[u8], num_chars: usize) -> String { pub fn get_random_string(alphabet: &[u8], num_chars: usize) -> String {
// Ref: https://rust-lang-nursery.github.io/rust-cookbook/algorithms/randomness.html // Ref: https://rust-lang-nursery.github.io/rust-cookbook/algorithms/randomness.html
@ -77,18 +84,18 @@ pub fn get_random_string_alphanum(num_chars: usize) -> String {
get_random_string(ALPHABET, num_chars) get_random_string(ALPHABET, num_chars)
} }
pub fn generate_id(num_bytes: usize) -> String { pub fn generate_id<const N: usize>() -> String {
HEXLOWER.encode(&get_random(vec![0; num_bytes])) encode_random_bytes::<N>(HEXLOWER)
} }
pub fn generate_send_id() -> String { pub fn generate_send_id() -> String {
// Send IDs are globally scoped, so make them longer to avoid collisions. // Send IDs are globally scoped, so make them longer to avoid collisions.
generate_id(32) // 256 bits generate_id::<32>() // 256 bits
} }
pub fn generate_attachment_id() -> String { pub fn generate_attachment_id() -> String {
// Attachment IDs are scoped to a cipher, so they can be smaller. // Attachment IDs are scoped to a cipher, so they can be smaller.
generate_id(10) // 80 bits generate_id::<10>() // 80 bits
} }
/// Generates a numeric token for email-based verifications. /// Generates a numeric token for email-based verifications.

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@ -48,7 +48,7 @@ impl Device {
use crate::crypto; use crate::crypto;
use data_encoding::BASE64; use data_encoding::BASE64;
let twofactor_remember = BASE64.encode(&crypto::get_random(vec![0u8; 180])); let twofactor_remember = crypto::encode_random_bytes::<180>(BASE64);
self.twofactor_remember = Some(twofactor_remember.clone()); self.twofactor_remember = Some(twofactor_remember.clone());
twofactor_remember twofactor_remember
@ -69,7 +69,7 @@ impl Device {
use crate::crypto; use crate::crypto;
use data_encoding::BASE64URL; use data_encoding::BASE64URL;
self.refresh_token = BASE64URL.encode(&crypto::get_random_64()); self.refresh_token = crypto::encode_random_bytes::<64>(BASE64URL);
} }
// Update the expiration of the device and the last update date // Update the expiration of the device and the last update date