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Pass a Signing() object 'signer' to Package() and Package.sign_firmware(),
instead of a 'key_file' string (path).

Access the private key only once, when generating 'signer', which:

1. Fixes a security issue where caller must write private key to disk
instead of passing it purely in memory eg:

    nrfutil --key-file $(secure-key-retrieval)

2. Gives a small speed improvement.

Fixes #327

Signed-off-by: Sirio Balmelli <>

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nRF Util

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nRF Util is a Python package and command-line utility that supports Device Firmware Updates (DFU) and cryptographic functionality.



See the InfoCenter pages for information on how to install and use nRF Util.


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