Properly pad user supplied hexadecimal strings to otp set subcommand

The library ultimately taking care of communicating with the Nitrokey
device, libnitrokey, unconditionally expects hexadecimal strings
supplied as part of the configuration of an OTP slot to have an even
number of bytes.
Users should not be aware of this detail and so with this change we take
care of padding the supplied string with a leading zero to make such a
configuration go through without an error.

1 files changed, 13 insertions, 2 deletions

diff --git a/nitrocli/src/commands.rs b/nitrocli/src/commands.rs
index eac8549..a65f070 100644
--- a/nitrocli/src/commands.rs
+++ b/nitrocli/src/commands.rs
@@ -646,7 +646,7 @@ fn prepare_base32_secret(secret: &str) -> Result<String> {
 /// Configure a one-time password slot on the Nitrokey device.
 pub fn otp_set(
   ctx: &mut args::ExecCtx<'_>,
-  data: nitrokey::OtpSlotData,
+  mut data: nitrokey::OtpSlotData,
   algorithm: args::OtpAlgorithm,
   counter: u64,
   time_window: u16,
@@ -656,7 +656,18 @@ pub fn otp_set(
     let secret = match secret_format {
       args::OtpSecretFormat::Ascii => prepare_ascii_secret(&data.secret)?,
       args::OtpSecretFormat::Base32 => prepare_base32_secret(&data.secret)?,
-      args::OtpSecretFormat::Hex => data.secret,
+      args::OtpSecretFormat::Hex => {
+        // We need to ensure to provide a string with an even number of
+        // characters in it, just because that's what libnitrokey
+        // expects. So prepend a '0' if that is not the case.
+        // TODO: This code can be removed once upstream issue #164
+        //       (https://github.com/Nitrokey/libnitrokey/issues/164) is
+        //       addressed.
+        if data.secret.len() % 2 != 0 {
+          data.secret.insert(0, '0')
+        }
+        data.secret
+      }
     };
     let data = nitrokey::OtpSlotData { secret, ..data };
     let device = authenticate_admin(ctx, device)?;