Correctly pad bytes with zero in hex conversion

When reading a secret in ascii or base32 format from the user, we
perform a conversion of the potentially decoded string into hexadecimal
bytes, because that is what libnitrokey expects.
The format string we used in the conversion, however, did not account
for padding with a leading zero for single digit results. E.g., the
newline/line feed symbol '\n', which has a decimal value of 10 would
result in the string 'a' being produced, whereas '0a' would be the
correct result.
This change corrects the format string to fix this problem.

2 files changed, 9 insertions, 1 deletions

diff --git a/nitrocli/CHANGELOG.md b/nitrocli/CHANGELOG.md
index d74f7b8..07e03c5 100644
--- a/nitrocli/CHANGELOG.md
+++ b/nitrocli/CHANGELOG.md
@@ -7,6 +7,7 @@ Unreleased
 - Removed `storage status` subcommand
   - Moved its output into `status` command
 - Removed previously deprecated `--ascii` option from `otp set` command
+- Fixed wrong hexadecimal conversion used in `otp set` command
 - Bumped `libc` dependency to `0.2.62`
 - Bumped `cc` dependency to `1.0.40`
 
diff --git a/nitrocli/src/commands.rs b/nitrocli/src/commands.rs
index b5fc282..eac8549 100644
--- a/nitrocli/src/commands.rs
+++ b/nitrocli/src/commands.rs
@@ -616,7 +616,7 @@ pub fn otp_get(
 fn format_bytes(bytes: &[u8]) -> String {
   bytes
     .iter()
-    .map(|c| format!("{:x}", c))
+    .map(|c| format!("{:02x}", c))
     .collect::<Vec<_>>()
     .join("")
 }
@@ -956,4 +956,11 @@ mod tests {
     let result = prepare_ascii_secret("Österreich");
     assert!(result.is_err());
   }
+
+  #[test]
+  fn hex_string() {
+    assert_eq!(format_bytes(&[b' ']), "20");
+    assert_eq!(format_bytes(&[b' ', b' ']), "2020");
+    assert_eq!(format_bytes(&[b'\n', b'\n']), "0a0a");
+  }
 }