Increase length limit for email token generation

The current limit of 19 is an artifact of the implementation, which can be
easily rewritten in terms of a more general string generation function.
The new limit is 255 (max value of a `u8`); using a larger type would
probably be overkill.

5 files changed, 15 insertions, 43 deletions

diff --git a/.env.template b/.env.template
index 1f4c937f..8da88cdc 100644
--- a/.env.template
+++ b/.env.template
@@ -185,7 +185,7 @@
 # EMAIL_EXPIRATION_TIME=600
 
 ## Email token size
-## Number of digits in an email token (min: 6, max: 19).
+## Number of digits in an email 2FA token (min: 6, max: 255).
 ## Note that the Bitwarden clients are hardcoded to mention 6 digit codes regardless of this setting!
 # EMAIL_TOKEN_SIZE=6
 
diff --git a/src/api/core/accounts.rs b/src/api/core/accounts.rs
index ead05478..32c81e93 100644
--- a/src/api/core/accounts.rs
+++ b/src/api/core/accounts.rs
@@ -381,7 +381,7 @@ fn post_email_token(data: JsonUpcase<EmailTokenData>, headers: Headers, conn: Db
         err!("Email domain not allowed");
     }
 
-    let token = crypto::generate_token(6)?;
+    let token = crypto::generate_email_token(6);
 
     if CONFIG.mail_enabled() {
         if let Err(e) = mail::send_change_email(&data.NewEmail, &token) {
diff --git a/src/api/core/two_factor/email.rs b/src/api/core/two_factor/email.rs
index 998aeccf..0753f62f 100644
--- a/src/api/core/two_factor/email.rs
+++ b/src/api/core/two_factor/email.rs
@@ -58,7 +58,7 @@ pub fn send_token(user_uuid: &str, conn: &DbConn) -> EmptyResult {
     let type_ = TwoFactorType::Email as i32;
     let mut twofactor = TwoFactor::find_by_user_and_type(user_uuid, type_, conn).map_res("Two factor not found")?;
 
-    let generated_token = crypto::generate_token(CONFIG.email_token_size())?;
+    let generated_token = crypto::generate_email_token(CONFIG.email_token_size());
 
     let mut twofactor_data = EmailTokenData::from_json(&twofactor.data)?;
     twofactor_data.set_token(generated_token);
@@ -123,7 +123,7 @@ fn send_email(data: JsonUpcase<SendEmailData>, headers: Headers, conn: DbConn) -
         tf.delete(&conn)?;
     }
 
-    let generated_token = crypto::generate_token(CONFIG.email_token_size())?;
+    let generated_token = crypto::generate_email_token(CONFIG.email_token_size());
     let twofactor_data = EmailTokenData::new(data.Email, generated_token);
 
     // Uses EmailVerificationChallenge as type to show that it's not verified yet.
@@ -309,18 +309,4 @@ mod tests {
         // If it's smaller than 3 characters it should only show asterisks.
         assert_eq!(result, "***@example.ext");
     }
-
-    #[test]
-    fn test_token() {
-        let result = crypto::generate_token(19).unwrap();
-
-        assert_eq!(result.chars().count(), 19);
-    }
-
-    #[test]
-    fn test_token_too_large() {
-        let result = crypto::generate_token(20);
-
-        assert!(result.is_err(), "too large token should give an error");
-    }
 }
diff --git a/src/config.rs b/src/config.rs
index 92fe8b9d..9e1f5e56 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -593,8 +593,8 @@ make_config! {
     email_2fa: _enable_email_2fa {
         /// Enabled |> Disabling will prevent users from setting up new email 2FA and using existing email 2FA configured
         _enable_email_2fa:      bool,   true,   auto,    |c| c._enable_smtp && c.smtp_host.is_some();
-        /// Email token size |> Number of digits in an email token (min: 6, max: 19). Note that the Bitwarden clients are hardcoded to mention 6 digit codes regardless of this setting.
-        email_token_size:       u32,    true,   def,      6;
+        /// Email token size |> Number of digits in an email 2FA token (min: 6, max: 255). Note that the Bitwarden clients are hardcoded to mention 6 digit codes regardless of this setting.
+        email_token_size:       u8,     true,   def,      6;
         /// Token expiration time |> Maximum time in seconds a token is valid. The time the user has to open email client and copy token.
         email_expiration_time:  u64,    true,   def,      600;
         /// Maximum attempts |> Maximum attempts before an email token is reset and a new email will need to be sent
@@ -668,10 +668,6 @@ fn validate_config(cfg: &ConfigItems) -> Result<(), Error> {
         if cfg._enable_email_2fa && cfg.email_token_size < 6 {
             err!("`EMAIL_TOKEN_SIZE` has a minimum size of 6")
         }
-
-        if cfg._enable_email_2fa && cfg.email_token_size > 19 {
-            err!("`EMAIL_TOKEN_SIZE` has a maximum size of 19")
-        }
     }
 
     // Check if the icon blacklist regex is valid
diff --git a/src/crypto.rs b/src/crypto.rs
index e30439fc..be9680cb 100644
--- a/src/crypto.rs
+++ b/src/crypto.rs
@@ -6,8 +6,6 @@ use std::num::NonZeroU32;
 use data_encoding::HEXLOWER;
 use ring::{digest, hmac, pbkdf2};
 
-use crate::error::Error;
-
 static DIGEST_ALG: pbkdf2::Algorithm = pbkdf2::PBKDF2_HMAC_SHA256;
 const OUTPUT_LEN: usize = digest::SHA256_OUTPUT_LEN;
 
@@ -65,6 +63,12 @@ pub fn get_random_string(alphabet: &[u8], num_chars: usize) -> String {
         .collect()
 }
 
+/// Generates a random numeric string.
+pub fn get_random_string_numeric(num_chars: usize) -> String {
+    const ALPHABET: &[u8] = b"0123456789";
+    get_random_string(ALPHABET, num_chars)
+}
+
 /// Generates a random alphanumeric string.
 pub fn get_random_string_alphanum(num_chars: usize) -> String {
     const ALPHABET: &[u8] = b"ABCDEFGHIJKLMNOPQRSTUVWXYZ\
@@ -87,23 +91,9 @@ pub fn generate_attachment_id() -> String {
     generate_id(10) // 80 bits
 }
 
-pub fn generate_token(token_size: u32) -> Result<String, Error> {
-    // A u64 can represent all whole numbers up to 19 digits long.
-    if token_size > 19 {
-        err!("Token size is limited to 19 digits")
-    }
-
-    let low: u64 = 0;
-    let high: u64 = 10u64.pow(token_size);
-
-    // Generate a random number in the range [low, high), then format it as a
-    // token of fixed width, left-padding with 0 as needed.
-    use rand::{thread_rng, Rng};
-    let mut rng = thread_rng();
-    let number: u64 = rng.gen_range(low..high);
-    let token = format!("{:0size$}", number, size = token_size as usize);
-
-    Ok(token)
+/// Generates a numeric token for email-based verifications.
+pub fn generate_email_token(token_size: u8) -> String {
+    get_random_string_numeric(token_size as usize)
 }
 
 /// Generates a personal API key.