The "Sign Text File" command can be found here:
Advanced > MicroSD Card > Sign Text File.
First step is to choose a suitable text file to be signed. It must meet these requirements:
The file should contain a single line of text to be signed. If there is a second line, it specifies the subkey derivation path for the key to be used for signing. Files that do not meet these requirements will not be offered for signing purposes.
The key subpath is optional and specifies a path from master key, such as
m/48'/0'/0' or similar. If not provided, the master key (
m) is used as a default.
Once a file has been selected, you'll be shown the message to be signed, and the subpath and address that will be used. You should press OK (✔) to proceed, and a new text file is created and saved with the signature added.
There are restrictions on the message to be signed, including:
These restrictions are also applied to messages signed using the USB protocol.
Here is a full example. Starting with this text file:
This sequence is shown on the COLDCARD:
signme2-signed.txt on the microSD card:
-----BEGIN BITCOIN SIGNED MESSAGE----- to-be-signed -----BEGIN SIGNATURE----- 1MDhJdtwjtGGbz3vQipUwtgjn5JPT2gWcT H9JPn0tbPfDVRVC48YnAOwbYKTCFQ5hvimrBAPyRtuzjPxM+hbDCGk+CvtTt/BJrJZkgJi9/UAKyrnbyi0kBsM4= -----END BITCOIN SIGNED MESSAGE-----
If you specify a path that conforms
we will assume you want
the address to be shown in Segwit/Bech32 P2PKH format, rather than
classic Bitcoin base58 format. Any path that starts with
get this treatment. The signature value itself is not impacted by this change.
We've found relevant search results.