scalpel

A scalpel and stitch tool for binaries. Maybe also a signing tool, maybe.

Snip around, stich up and/or sign binaries

This is mostly used for the case where parts of the binary need to be extracted or replaced.

Use Cases

• cut firmware into pieces from an all-in-one blob

  scalpel cut --start 0 --end 4Ki --output bootloader.bin firmware.bin
  scalpel cut --start 4Ki --size 241664 --output part_A.bin firmware.bin
  scalpel cut --start 282624 --size 241664 --output part_B.bin firmware.bin

• stitch firmware pieces together such as bootloader and application

  scalpel stitch --binary tmp/test_bytes --offset 0    --binary tmp/test_bytes --offset 2048 --fill-pattern zero --output stitched.bin
  scalpel stitch --binary tmp/test_bytes --offset 2Ki --binary tmp/test_bytes --offset 0 --fill-pattern one --output stitched.bin
  scalpel stitch --binary tmp/test_bytes --offset 2058 --binary tmp/test_bytes --offset 10 --fill-pattern random --output stitched.bin

• replace a section with a new file

  scalpel replace --start 1Ki --end 2Ki --replace tmp/test_cut_out --output cut tmp/test_bytes
  scalpel replace --end 2Ki --replace tmp/test_cut_out --output cut tmp/test_bytes
  scalpel replace --start 1Ki --size 1Ki --replace tmp/test_cut_out --output cut tmp/test_bytes

• [alpha] sign firmware for authenticity

  scalpel sign tmp/ed25519_keypair.pk8 --format pkcs8 tmp/signme.bin
  scalpel sign tmp/ed25519_keypair.pk8 --output tmp/signme_signed.bin tmp/signme.bin
  scalpel sign tmp/ed25519_keypair.pk8 tmp/test_bytes tmp/signme.bin

Features

• cut off a binary at specific start and end/size
• Add signature verification and appendix features (using preferably ring and [webpki] or as an alternative [sodiumoxide] (linking it statically))
• Handle endianness of checksums properly
• Replace parts (i.e. cert files or non volatile memory and/or sections) (with resigning if necessary)
• Allow hexadecimal input
• Allow multipile input scales (K = 1000, Ki = 1024, M = 1e6, Mi = 1024*1024, ...)
• Add verifier option for alignment to given sector/page size

Common / Hints

• You need th extracted binary as include? Use xxd -i sliced.bin > sliced_binary.h to create a header file out of the result.

• Convert RSA keys in .pem format to pkcs8 format via openssl (see ring doc doc-ring ), openssl supports Ed25519 algorithm currently only on master branch

  openssl pkcs8 -toppk8 -nocrypt -outform der -in [key.pem] > [pkcs8_key.pk8]

• Generate valid Ed25519 Keypair use small tool from ring author:

  cargo install kt
  kt generate ed25519 --out=FILE