Allowing for message signature the line feed (LF) character handled by NBGL
What the developer wrote
Authored by Ilya Artemov
Allowing for message signature the line feed (LF) character handled by NBGL
What changed, and why it matters
This commit changes how the Ledger Bitcoin app decides whether a message being signed is 'printable' on the device screen. It now allows the Line Feed (newline) character to pass through, because the newer NBGL screen library can display multi-line text. Previously, any character outside the normal visible ASCII range would make the message be shown as a hex dump instead of readable text. The change is a small UI/UX improvement for message signing and does not appear to alter the actual cryptographic signature.
No immediate action required. Treat as a routine UI compatibility update. If reviewing for security, verify that the newline exception cannot be abused to mislead users (e.g., by truncating or visually splitting a message in a deceptive way), and confirm that the message hash/signature path is independent of the printable flag.
Security signals we found
UI display validation relaxation
Non-printable ASCII character exception added
No cryptographic code changed
Evidence from the diff
In src/handler/sign_message.c, the loop that validates each byte of a message chunk for display purposes previously marked the message as non-printable if any byte was outside 0x20-0x7E. The patch adds an exception for the newline character (0x0A/’\n’), because the NBGL UI framework can render line breaks. The signature path itself is unchanged; this only affects how the message is presented to the user for approval on the device screen.
Changed components
src/handler/sign_message.cmessage signing display flowInspect captured patch +3 / −1
diff --git a/src/handler/sign_message.c b/src/handler/sign_message.c
index acf8a24..159f9a4 100644
--- a/src/handler/sign_message.c
+++ b/src/handler/sign_message.c
@@ -104,7 +104,9 @@ void handler_sign_message(dispatcher_context_t *dc, uint8_t protocol_version) {
if (printable) {
for (int j = 0; j < chunk_len; j++) {
- if (message_chunk[j] < 0x20 || message_chunk[j] > 0x7E) {
+ // Line Feed (LF) character is handled by NBGL - let's allow it
+ if ((message_chunk[j] < 0x20 || message_chunk[j] > 0x7E) &&
+ (message_chunk[j] != '\n')) {
printable = false;
break;
}
Why this scored 20/100
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